Log DB table names.

Pass memory stats from main process to crash reporter process

See merge request briar/briar!1662

.gitlab-ci.yml

@@ -98,6 +98,7 @@ bridge test:
       allow_failure: true
   script:
     - OPTIONAL_TESTS=org.briarproject.bramble.plugin.tor.BridgeTest ./gradlew --info bramble-java:test --tests BridgeTest
+  timeout: 3h
 
 mailbox integration test:
   extends: .optional_tests
@@ -117,10 +118,3 @@ mailbox integration test:
     - cd "$CI_PROJECT_DIR"
     - bramble-core/src/test/bash/wait-for-mailbox.sh
     - OPTIONAL_TESTS=org.briarproject.bramble.mailbox.MailboxIntegrationTest ./gradlew --info bramble-core:test --tests MailboxIntegrationTest
-
-pre_release_tests:
-  extends: .optional_tests
-  script:
-    - OPTIONAL_TESTS=org.briarproject.bramble.plugin.tor.BridgeTest ./gradlew --info bramble-java:test --tests BridgeTest
-  only:
-    - tags

bramble-android/build.gradle

@@ -15,8 +15,8 @@ android {
 	defaultConfig {
 		minSdkVersion 16
 		targetSdkVersion 30
-		versionCode 10405
-		versionName "1.4.5"
+		versionCode 10408
+		versionName "1.4.8"
 		consumerProguardFiles 'proguard-rules.txt'
 
 		testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
@@ -43,7 +43,7 @@ configurations {
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
 	tor "org.briarproject:tor-android:$tor_version"
-	tor "org.briarproject:obfs4proxy-android:$obfs4proxy_version@zip"
+	tor "org.briarproject:obfs4proxy-android:$obfs4proxy_version"
 
 	annotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
 
@@ -70,11 +70,6 @@ clean.dependsOn cleanTorBinaries
 
 task unpackTorBinaries {
 	doLast {
-		copy {
-			from configurations.tor.collect { zipTree(it) }
-			into torBinariesDir
-			include 'geoip.zip'
-		}
 		configurations.tor.each { outer ->
 			zipTree(outer).each { inner ->
 				if (inner.name.endsWith('_arm_pie.zip')) {

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

@@ -11,7 +11,10 @@ import android.net.LinkAddress;
 import android.net.LinkProperties;
 import android.net.Network;
 import android.net.NetworkInfo;
+import android.net.wifi.WifiInfo;
+import android.net.wifi.WifiManager;
 
+import org.briarproject.bramble.api.Cancellable;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.lifecycle.Service;
@@ -21,7 +24,6 @@ import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.system.TaskScheduler;
-import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
 
 import java.net.Inet4Address;
 import java.net.InetAddress;
@@ -38,6 +40,7 @@ import javax.annotation.Nullable;
 import javax.inject.Inject;
 
 import static android.content.Context.CONNECTIVITY_SERVICE;
+import static android.content.Context.WIFI_SERVICE;
 import static android.content.Intent.ACTION_SCREEN_OFF;
 import static android.content.Intent.ACTION_SCREEN_ON;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
@@ -111,15 +114,37 @@ class AndroidNetworkManager implements NetworkManager, Service {
 
 	@Override
 	public NetworkStatus getNetworkStatus() {
-		NetworkInfo net = connectivityManager.getActiveNetworkInfo();
-		boolean connected = net != null && net.isConnected();
-		boolean wifi = false, ipv6Only = false;
-		if (connected) {
-			wifi = net.getType() == TYPE_WIFI;
-			if (SDK_INT >= 23) ipv6Only = isActiveNetworkIpv6Only();
-			else ipv6Only = areAllAvailableNetworksIpv6Only();
+		// https://issuetracker.google.com/issues/175055271
+		try {
+			NetworkInfo net = connectivityManager.getActiveNetworkInfo();
+			boolean connected = net != null && net.isConnected();
+			boolean wifi = false, ipv6Only = false;
+			if (connected) {
+				wifi = net.getType() == TYPE_WIFI;
+				if (SDK_INT >= 23) ipv6Only = isActiveNetworkIpv6Only();
+				else ipv6Only = areAllAvailableNetworksIpv6Only();
+			}
+			return new NetworkStatus(connected, wifi, ipv6Only);
+		} catch (SecurityException e) {
+			logException(LOG, WARNING, e);
+			// Without the ConnectivityManager we can't detect whether we have
+			// internet access. Assume we do, which is probably less harmful
+			// than assuming we don't. Likewise, assume the connection is
+			// IPv6-only. Fall back to the WifiManager to detect whether we
+			// have a wifi connection.
+			LOG.info("ConnectivityManager is broken, guessing connectivity");
+			boolean connected = true, wifi = false, ipv6Only = true;
+			WifiManager wm = (WifiManager) app.getSystemService(WIFI_SERVICE);
+			if (wm != null) {
+				WifiInfo info = wm.getConnectionInfo();
+				if (info != null && info.getIpAddress() != 0) {
+					LOG.info("Connected to wifi");
+					wifi = true;
+					ipv6Only = false;
+				}
+			}
+			return new NetworkStatus(connected, wifi, ipv6Only);
 		}
-		return new NetworkStatus(connected, wifi, ipv6Only);
 	}
 
 	/**
@@ -130,23 +155,29 @@ class AndroidNetworkManager implements NetworkManager, Service {
 	 */
 	@TargetApi(23)
 	private boolean isActiveNetworkIpv6Only() {
-		Network net = connectivityManager.getActiveNetwork();
-		if (net == null) {
-			LOG.info("No active network");
+		// https://issuetracker.google.com/issues/175055271
+		try {
+			Network net = connectivityManager.getActiveNetwork();
+			if (net == null) {
+				LOG.info("No active network");
+				return false;
+			}
+			LinkProperties props = connectivityManager.getLinkProperties(net);
+			if (props == null) {
+				LOG.info("No link properties for active network");
+				return false;
+			}
+			boolean hasIpv6Unicast = false;
+			for (LinkAddress linkAddress : props.getLinkAddresses()) {
+				InetAddress addr = linkAddress.getAddress();
+				if (addr instanceof Inet4Address) return false;
+				if (!addr.isMulticastAddress()) hasIpv6Unicast = true;
+			}
+			return hasIpv6Unicast;
+		} catch (SecurityException e) {
+			logException(LOG, WARNING, e);
 			return false;
 		}
-		LinkProperties props = connectivityManager.getLinkProperties(net);
-		if (props == null) {
-			LOG.info("No link properties for active network");
-			return false;
-		}
-		boolean hasIpv6Unicast = false;
-		for (LinkAddress linkAddress : props.getLinkAddresses()) {
-			InetAddress addr = linkAddress.getAddress();
-			if (addr instanceof Inet4Address) return false;
-			if (!addr.isMulticastAddress()) hasIpv6Unicast = true;
-		}
-		return hasIpv6Unicast;
 	}
 
 	/**

bramble-android/src/main/java/org/briarproject/bramble/plugin/file/AndroidRemovableDrivePlugin.java

@@ -32,13 +32,22 @@ class AndroidRemovableDrivePlugin extends RemovableDrivePlugin {
 	InputStream openInputStream(TransportProperties p) throws IOException {
 		String uri = p.get(PROP_URI);
 		if (isNullOrEmpty(uri)) throw new IllegalArgumentException();
-		return app.getContentResolver().openInputStream(Uri.parse(uri));
+		try {
+			return app.getContentResolver().openInputStream(Uri.parse(uri));
+		} catch (SecurityException e) {
+			throw new IOException(e);
+		}
 	}
 
 	@Override
 	OutputStream openOutputStream(TransportProperties p) throws IOException {
 		String uri = p.get(PROP_URI);
 		if (isNullOrEmpty(uri)) throw new IllegalArgumentException();
-		return app.getContentResolver().openOutputStream(Uri.parse(uri));
+		try {
+			return app.getContentResolver()
+					.openOutputStream(Uri.parse(uri), "wt");
+		} catch (SecurityException e) {
+			throw new IOException(e);
+		}
 	}
 }

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

@@ -175,16 +175,24 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 	@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;
+		// https://issuetracker.google.com/issues/175055271
+		try {
+			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;
+				}
 			}
+		} catch (SecurityException e) {
+			logException(LOG, WARNING, e);
 		}
 		return null;
 	}
@@ -227,12 +235,17 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 	// network's socket factory may try to connect via another network
 	private SocketFactory getSocketFactory() {
 		if (SDK_INT < 21) return SocketFactory.getDefault();
-		for (Network net : connectivityManager.getAllNetworks()) {
-			NetworkCapabilities caps =
-					connectivityManager.getNetworkCapabilities(net);
-			if (caps != null && caps.hasTransport(TRANSPORT_WIFI)) {
-				return net.getSocketFactory();
+		// https://issuetracker.google.com/issues/175055271
+		try {
+			for (Network net : connectivityManager.getAllNetworks()) {
+				NetworkCapabilities caps =
+						connectivityManager.getNetworkCapabilities(net);
+				if (caps != null && caps.hasTransport(TRANSPORT_WIFI)) {
+					return net.getSocketFactory();
+				}
 			}
+		} catch (SecurityException e) {
+			logException(LOG, WARNING, e);
 		}
 		LOG.warning("Could not find suitable socket factory");
 		return SocketFactory.getDefault();

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

@@ -11,62 +11,35 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
 import org.briarproject.bramble.api.plugin.PluginCallback;
-import org.briarproject.bramble.api.plugin.TorConstants;
 import org.briarproject.bramble.api.plugin.TorControlPort;
 import org.briarproject.bramble.api.plugin.TorDirectory;
 import org.briarproject.bramble.api.plugin.TorSocksPort;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
-import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 import org.briarproject.bramble.api.system.WakefulIoExecutor;
-import org.briarproject.bramble.util.AndroidUtils;
 
 import java.io.File;
 import java.util.concurrent.Executor;
-import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 import javax.net.SocketFactory;
 
+import static org.briarproject.bramble.util.AndroidUtils.getSupportedArchitectures;
+
 @Immutable
 @NotNullByDefault
-public class AndroidTorPluginFactory implements DuplexPluginFactory {
+public class AndroidTorPluginFactory extends TorPluginFactory {
 
-	private static final Logger LOG =
-			Logger.getLogger(AndroidTorPluginFactory.class.getName());
-
-	private static final int MAX_LATENCY = 30 * 1000; // 30 seconds
-	private static final int MAX_IDLE_TIME = 30 * 1000; // 30 seconds
-	private static final int MIN_POLLING_INTERVAL = 60 * 1000; // 1 minute
-	private static final int MAX_POLLING_INTERVAL = 10 * 60 * 1000; // 10 mins
-	private static final double BACKOFF_BASE = 1.2;
-
-	private final Executor ioExecutor, wakefulIoExecutor;
 	private final Application app;
-	private final NetworkManager networkManager;
-	private final LocationUtils locationUtils;
-	private final EventBus eventBus;
-	private final SocketFactory torSocketFactory;
-	private final BackoffFactory backoffFactory;
-	private final ResourceProvider resourceProvider;
-	private final CircumventionProvider circumventionProvider;
-	private final BatteryManager batteryManager;
 	private final AndroidWakeLockManager wakeLockManager;
-	private final Clock clock;
-	private final File torDirectory;
-	private int torSocksPort;
-	private int torControlPort;
-	private final CryptoComponent crypto;
 
 	@Inject
 	AndroidTorPluginFactory(@IoExecutor Executor ioExecutor,
 			@WakefulIoExecutor Executor wakefulIoExecutor,
-			Application app,
 			NetworkManager networkManager,
 			LocationUtils locationUtils,
 			EventBus eventBus,
@@ -75,80 +48,43 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
 			BatteryManager batteryManager,
-			AndroidWakeLockManager wakeLockManager,
 			Clock clock,
+			CryptoComponent crypto,
 			@TorDirectory File torDirectory,
 			@TorSocksPort int torSocksPort,
 			@TorControlPort int torControlPort,
-			CryptoComponent crypto) {
-		this.ioExecutor = ioExecutor;
-		this.wakefulIoExecutor = wakefulIoExecutor;
+			Application app,
+			AndroidWakeLockManager wakeLockManager) {
+		super(ioExecutor, wakefulIoExecutor, networkManager, locationUtils,
+				eventBus, torSocketFactory, backoffFactory, resourceProvider,
+				circumventionProvider, batteryManager, clock, crypto,
+				torDirectory, torSocksPort, torControlPort);
 		this.app = app;
-		this.networkManager = networkManager;
-		this.locationUtils = locationUtils;
-		this.eventBus = eventBus;
-		this.torSocketFactory = torSocketFactory;
-		this.backoffFactory = backoffFactory;
-		this.resourceProvider = resourceProvider;
-		this.circumventionProvider = circumventionProvider;
-		this.batteryManager = batteryManager;
 		this.wakeLockManager = wakeLockManager;
-		this.clock = clock;
-		this.torDirectory = torDirectory;
-		this.torSocksPort = torSocksPort;
-		this.torControlPort = torControlPort;
-		this.crypto = crypto;
 	}
 
+	@Nullable
 	@Override
-	public TransportId getId() {
-		return TorConstants.ID;
-	}
-
-	@Override
-	public long getMaxLatency() {
-		return MAX_LATENCY;
-	}
-
-	@Override
-	public DuplexPlugin createPlugin(PluginCallback callback) {
-
-		// Check that we have a Tor binary for this architecture
-		String architecture = null;
-		for (String abi : AndroidUtils.getSupportedArchitectures()) {
-			if (abi.startsWith("x86_64")) {
-				architecture = "x86_64";
-				break;
-			} else if (abi.startsWith("x86")) {
-				architecture = "x86";
-				break;
-			} else if (abi.startsWith("arm64")) {
-				architecture = "arm64";
-				break;
-			} else if (abi.startsWith("armeabi")) {
-				architecture = "arm";
-				break;
-			}
+	String getArchitectureForTorBinary() {
+		for (String abi : getSupportedArchitectures()) {
+			if (abi.startsWith("x86_64")) return "x86_64_pie";
+			else if (abi.startsWith("x86")) return "x86_pie";
+			else if (abi.startsWith("arm64")) return "arm64_pie";
+			else if (abi.startsWith("armeabi")) return "arm_pie";
 		}
-		if (architecture == null) {
-			LOG.info("Tor is not supported on this architecture");
-			return null;
-		}
-		// Use position-independent executable
-		architecture += "_pie";
+		return null;
+	}
 
-		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
-				MAX_POLLING_INTERVAL, BACKOFF_BASE);
-		TorRendezvousCrypto torRendezvousCrypto =
-				new TorRendezvousCryptoImpl(crypto);
-		AndroidTorPlugin plugin = new AndroidTorPlugin(ioExecutor,
+	@Override
+	TorPlugin createPluginInstance(Backoff backoff,
+			TorRendezvousCrypto torRendezvousCrypto, PluginCallback callback,
+			String architecture) {
+		return new AndroidTorPlugin(ioExecutor,
 				wakefulIoExecutor, app, networkManager, locationUtils,
 				torSocketFactory, clock, resourceProvider,
 				circumventionProvider, batteryManager, wakeLockManager,
 				backoff, torRendezvousCrypto, callback, architecture,
 				MAX_LATENCY, MAX_IDLE_TIME, torDirectory, torSocksPort,
 				torControlPort);
-		eventBus.addListener(plugin);
-		return plugin;
 	}
 }

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

@@ -8,6 +8,7 @@ import android.content.Intent;
 import android.os.Process;
 import android.os.SystemClock;
 
+import org.briarproject.bramble.api.Cancellable;
 import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.AlarmListener;
@@ -116,10 +117,12 @@ class AndroidTaskScheduler implements TaskScheduler, Service, AlarmListener {
 		long dueMillis = now + MILLISECONDS.convert(delay, unit);
 		Runnable wakeful = () ->
 				wakeLockManager.executeWakefully(task, executor, "TaskHandoff");
-		Future<?> check = scheduleCheckForDueTasks(delay, unit);
-		ScheduledTask s = new ScheduledTask(wakeful, dueMillis, check,
-				cancelled);
+		// Acquire the lock before scheduling the check to ensure the check
+		// doesn't access the task queue before the task has been added
+		ScheduledTask s;
 		synchronized (lock) {
+			Future<?> check = scheduleCheckForDueTasks(delay, unit);
+			s = new ScheduledTask(wakeful, dueMillis, check, cancelled);
 			tasks.add(s);
 		}
 		return s;
@@ -136,6 +139,7 @@ class AndroidTaskScheduler implements TaskScheduler, Service, AlarmListener {
 		return schedule(wrapped, executor, delay, unit, cancelled);
 	}
 
+	@GuardedBy("lock")
 	private Future<?> scheduleCheckForDueTasks(long delay, TimeUnit unit) {
 		Runnable wakeful = () -> wakeLockManager.runWakefully(
 				this::runDueTasks, "TaskScheduler");
@@ -206,7 +210,7 @@ class AndroidTaskScheduler implements TaskScheduler, Service, AlarmListener {
 		private final Future<?> check;
 		private final AtomicBoolean cancelled;
 
-		public ScheduledTask(Runnable task, long dueMillis,
+		private ScheduledTask(Runnable task, long dueMillis,
 				Future<?> check, AtomicBoolean cancelled) {
 			this.task = task;
 			this.dueMillis = dueMillis;

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

@@ -4,6 +4,7 @@ import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothAdapter;
 import android.content.Context;
 import android.os.Build;
+import android.os.Looper;
 import android.provider.Settings;
 
 import org.briarproject.bramble.api.Pair;
@@ -134,4 +135,8 @@ public class AndroidUtils {
 			return null;
 		}
 	}
+
+	public static boolean isUiThread() {
+		return Looper.myLooper() == Looper.getMainLooper();
+	}
 }

bramble-android/witness.gradle

@@ -87,8 +87,8 @@ dependencyVerification {
         'org.apache.httpcomponents:httpmime:4.5.6:httpmime-4.5.6.jar:0b2b1102c18d3c7e05a77214b9b7501a6f6056174ae5604e0e256776eda7553e',
         'org.bouncycastle:bcpkix-jdk15on:1.56:bcpkix-jdk15on-1.56.jar:7043dee4e9e7175e93e0b36f45b1ec1ecb893c5f755667e8b916eb8dd201c6ca',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
-        'org.briarproject:obfs4proxy-android:0.0.12-dev-40245c4a:obfs4proxy-android-0.0.12-dev-40245c4a.zip:8ab05a8f8391be2cb5ab2b665c281a06d9e3a756bd0f95a40a36ca927866ea82',
-        'org.briarproject:tor-android:0.3.5.17:tor-android-0.3.5.17.jar:1888afc10a26b93d00a010ea27bf0b1b162a6d524688b08b98d70d14dc363b54',
+        'org.briarproject:obfs4proxy-android:0.0.12:obfs4proxy-android-0.0.12.jar:84159d2a4668abc40e3fccaa1f6fa0c04892863f9eb80a866ac8928d9f9a7e89',
+        'org.briarproject:tor-android:0.4.5.12-2:tor-android-0.4.5.12-2.jar:8545dbcef2bb6aa89c32bb6f8ac51f7a64bce3ae85845b3578ffdeb9b206feb9',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
         'org.checkerframework:checker-qual:3.5.0:checker-qual-3.5.0.jar:729990b3f18a95606fc2573836b6958bcdb44cb52bfbd1b7aa9c339cff35a5a4',

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

@@ -0,0 +1,6 @@
+package org.briarproject.bramble.api;
+
+public interface Cancellable {
+
+	void cancel();
+}

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

@@ -1,8 +1,14 @@
 package org.briarproject.bramble.api;
 
+import org.briarproject.bramble.util.StringUtils;
+
+import java.util.ArrayList;
 import java.util.Hashtable;
+import java.util.List;
 import java.util.Map;
 
+import javax.annotation.Nullable;
+
 public abstract class StringMap extends Hashtable<String, String> {
 
 	protected StringMap(Map<String, String> m) {
@@ -52,4 +58,31 @@ public abstract class StringMap extends Hashtable<String, String> {
 	public void putLong(String key, long value) {
 		put(key, String.valueOf(value));
 	}
+
+	@Nullable
+	public int[] getIntArray(String key) {
+		String s = get(key);
+		if (s == null) return null;
+		// Handle empty string because "".split(",") returns {""}
+		if (s.length() == 0) return new int[0];
+		String[] intStrings = s.split(",");
+		int[] ints = new int[intStrings.length];
+		try {
+			for (int i = 0; i < ints.length; i++) {
+				ints[i] = Integer.parseInt(intStrings[i]);
+			}
+		} catch (NumberFormatException e) {
+			return null;
+		}
+		return ints;
+	}
+
+	public void putIntArray(String key, int[] value) {
+		List<String> intStrings = new ArrayList<>();
+		for (int integer : value) {
+			intStrings.add(String.valueOf(integer));
+		}
+		// Puts empty string if input array value is empty
+		put(key, StringUtils.join(intStrings, ","));
+	}
 }

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

@@ -6,14 +6,14 @@ import javax.annotation.concurrent.ThreadSafe;
 
 @ThreadSafe
 @NotNullByDefault
-public abstract class UniqueId extends Bytes {
+public class UniqueId extends Bytes {
 
 	/**
 	 * The length of a unique identifier in bytes.
 	 */
 	public static final int LENGTH = 32;
 
-	protected UniqueId(byte[] id) {
+	public UniqueId(byte[] id) {
 		super(id);
 		if (id.length != LENGTH) throw new IllegalArgumentException();
 	}

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

@@ -9,6 +9,8 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.properties.TransportProperties;
@@ -18,6 +20,7 @@ import org.briarproject.bramble.api.sync.MessageId;
 
 import java.security.GeneralSecurityException;
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 
 @NotNullByDefault
@@ -123,6 +126,19 @@ public interface ClientHelper {
 	Map<TransportId, TransportProperties> parseAndValidateTransportPropertiesMap(
 			BdfDictionary properties) throws FormatException;
 
+	/**
+	 * Parse and validate the elements of a Mailbox update message.
+	 *
+	 * @return the parsed update message
+	 * @throws FormatException if the message elements are invalid
+	 */
+	MailboxUpdate parseAndValidateMailboxUpdate(BdfList clientSupports,
+			BdfList serverSupports, BdfDictionary properties)
+			throws FormatException;
+
+	List<MailboxVersion> parseMailboxVersionList(BdfList bdfList)
+			throws FormatException;
+
 	/**
 	 * Retrieves the contact ID from the group metadata of the given contact
 	 * group.

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

@@ -16,6 +16,17 @@ public interface ConnectionManager {
 	 */
 	void manageIncomingConnection(TransportId t, TransportConnectionReader r);
 
+	/**
+	 * Manages an incoming connection from a contact via a mailbox.
+	 * <p>
+	 * This method does not mark the tag as recognised until after the data
+	 * has been read from the {@link TransportConnectionReader}, at which
+	 * point the {@link TagController} is called to decide whether the tag
+	 * should be marked as recognised.
+	 */
+	void manageIncomingConnection(TransportId t, TransportConnectionReader r,
+			TagController c);
+
 	/**
 	 * Manages an incoming connection from a contact over a duplex transport.
 	 */
@@ -46,4 +57,21 @@ public interface ConnectionManager {
 	 */
 	void manageOutgoingConnection(PendingContactId p, TransportId t,
 			DuplexTransportConnection d);
+
+	/**
+	 * An interface for controlling whether a tag should be marked as
+	 * recognised.
+	 */
+	interface TagController {
+		/**
+		 * This method is only called if a tag was read from the corresponding
+		 * {@link TransportConnectionReader} and recognised.
+		 *
+		 * @param exception True if an exception was thrown while reading from
+		 * the {@link TransportConnectionReader}, after successfully reading
+		 * and recognising the tag.
+		 * @return True if the tag should be marked as recognised.
+		 */
+		boolean shouldMarkTagAsRecognised(boolean exception);
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContactId.java

@@ -3,7 +3,6 @@ package org.briarproject.bramble.api.contact;
 import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
-import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 
 /**
@@ -17,9 +16,4 @@ public class PendingContactId extends UniqueId {
 	public PendingContactId(byte[] id) {
 		super(id);
 	}
-
-	@Override
-	public boolean equals(@Nullable Object o) {
-		return o instanceof PendingContactId && super.equals(o);
-	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/CryptoComponent.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.api.crypto;
 
+import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.security.GeneralSecurityException;
@@ -10,6 +11,8 @@ import javax.annotation.Nullable;
 @NotNullByDefault
 public interface CryptoComponent {
 
+	UniqueId generateUniqueId();
+
 	SecretKey generateSecretKey();
 
 	SecureRandom getSecureRandom();
@@ -172,9 +175,11 @@ public interface CryptoComponent {
 	String asciiArmour(byte[] b, int lineLength);
 
 	/**
-	 * Encode the onion/hidden service address given its public key. As
-	 * specified here: https://gitweb.torproject.org/torspec.git/tree/rend-spec-v3.txt?id=29245fd5#n2135
+	 * Encode the Onion given its public key. Specified here:
+	 * https://gitweb.torproject.org/torspec.git/tree/rend-spec-v3.txt?id=29245fd5#n2135
+	 *
+	 * @return the encoded onion, base32 chars
 	 */
-	String encodeOnionAddress(byte[] publicKey);
+	String encodeOnion(byte[] publicKey);
 
 }

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

@@ -33,11 +33,18 @@ import java.util.List;
 import java.util.Map;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.ThreadSafe;
 
 /**
  * Encapsulates the database implementation and exposes high-level operations
  * to other components.
+ * <p>
+ * With the exception of the {@link #open(SecretKey, MigrationListener)} and
+ * {@link #close()} methods, which must not be called concurrently, the
+ * database can be accessed from any thread. See {@link TransactionManager}
+ * for locking behaviour.
  */
+@ThreadSafe
 @NotNullByDefault
 public interface DatabaseComponent extends TransactionManager {
 
@@ -193,26 +200,15 @@ public interface DatabaseComponent extends TransactionManager {
 			throws DbException;
 
 	/**
-	 * Returns a batch of messages for the given contact, with a total length
-	 * less than or equal to the given length, for transmission over a
-	 * transport with the given maximum latency. Returns null if there are no
-	 * sendable messages that fit in the given length.
+	 * Returns a batch of messages for the given contact, for transmission over
+	 * a transport with the given maximum latency. The total length of the
+	 * messages, including record headers, will be no more than the given
+	 * capacity. Returns null if there are no sendable messages that would fit
+	 * in the given capacity.
 	 */
 	@Nullable
 	Collection<Message> generateBatch(Transaction txn, ContactId c,
-			int maxLength, long maxLatency) throws DbException;
-
-	/**
-	 * Returns a batch of messages for the given contact containing the
-	 * messages with the given IDs, for transmission over a transport with
-	 * the given maximum latency.
-	 * <p/>
-	 * If any of the given messages are not in the database or are not visible
-	 * to the contact, they are omitted from the batch without throwing an
-	 * exception.
-	 */
-	Collection<Message> generateBatch(Transaction txn, ContactId c,
-			Collection<MessageId> ids, long maxLatency) throws DbException;
+			long capacity, long maxLatency) throws DbException;
 
 	/**
 	 * Returns an offer for the given contact for transmission over a
@@ -232,15 +228,16 @@ public interface DatabaseComponent extends TransactionManager {
 			throws DbException;
 
 	/**
-	 * Returns a batch of messages for the given contact, with a total length
-	 * less than or equal to the given length, for transmission over a
-	 * transport with the given maximum latency. Only messages that have been
-	 * requested by the contact are returned. Returns null if there are no
-	 * sendable messages that fit in the given length.
+	 * Returns a batch of messages for the given contact, for transmission over
+	 * a transport with the given maximum latency. Only messages that have been
+	 * requested by the contact are returned. The total length of the messages,
+	 * including record headers, will be no more than the given capacity.
+	 * Returns null if there are no sendable messages that have been requested
+	 * by the contact and would fit in the given capacity.
 	 */
 	@Nullable
 	Collection<Message> generateRequestedBatch(Transaction txn, ContactId c,
-			int maxLength, long maxLatency) throws DbException;
+			long capacity, long maxLatency) throws DbException;
 
 	/**
 	 * Returns the contact with the given ID.
@@ -344,6 +341,30 @@ public interface DatabaseComponent extends TransactionManager {
 	Collection<MessageId> getMessageIds(Transaction txn, GroupId g,
 			Metadata query) throws DbException;
 
+	/**
+	 * Returns the IDs of some messages received from the given contact that
+	 * need to be acknowledged, up to the given number of messages.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<MessageId> getMessagesToAck(Transaction txn, ContactId c,
+			int maxMessages) throws DbException;
+
+	/**
+	 * Returns the IDs of some messages that are eligible to be sent to the
+	 * given contact over a transport with the given maximum latency. The total
+	 * length of the messages including record headers will be no more than the
+	 * given capacity.
+	 * <p/>
+	 * Unlike {@link #getUnackedMessagesToSend(Transaction, ContactId)} this
+	 * method does not return messages that have already been sent unless they
+	 * are due for retransmission.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<MessageId> getMessagesToSend(Transaction txn, ContactId c,
+			long capacity, long maxLatency) throws DbException;
+
 	/**
 	 * Returns the IDs of any messages that need to be validated.
 	 * <p/>
@@ -460,21 +481,36 @@ public interface DatabaseComponent extends TransactionManager {
 	MessageStatus getMessageStatus(Transaction txn, ContactId c, MessageId m)
 			throws DbException;
 
+	/**
+	 * Returns the message with the given ID for transmission to the given
+	 * contact over a transport with the given maximum latency. Returns null
+	 * if the message is no longer visible to the contact.
+	 *
+	 * @param markAsSent True if the message should be marked as sent.
+	 * If false it can be marked as sent by calling
+	 * {@link #setMessagesSent(Transaction, ContactId, Collection, long)}.
+	 */
+	@Nullable
+	Message getMessageToSend(Transaction txn, ContactId c, MessageId m,
+			long maxLatency, boolean markAsSent) throws DbException;
+
 	/**
 	 * Returns the IDs of all messages that are eligible to be sent to the
-	 * given contact, together with their raw lengths. This may include
-	 * messages that have already been sent and are not yet due for
-	 * retransmission.
+	 * given contact.
+	 * <p>
+	 * Unlike {@link #getMessagesToSend(Transaction, ContactId, long, long)}
+	 * this method may return messages that have already been sent and are
+	 * not yet due for retransmission.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, Integer> getUnackedMessagesToSend(Transaction txn,
+	Collection<MessageId> getUnackedMessagesToSend(Transaction txn,
 			ContactId c) throws DbException;
 
 	/**
-	 * Reset the transmission count, expiry time and ETA of all messages that
-	 * are eligible to be sent to the given contact. This includes messages that
-	 * have already been sent and are not yet due for retransmission.
+	 * Resets the transmission count, expiry time and max latency of all messages
+	 * that are eligible to be sent to the given contact. This includes messages
+	 * that have already been sent and are not yet due for retransmission.
 	 */
 	void resetUnackedMessagesToSend(Transaction txn, ContactId c)
 			throws DbException;
@@ -648,6 +684,13 @@ public interface DatabaseComponent extends TransactionManager {
 	void removeTransportKeys(Transaction txn, TransportId t, KeySetId k)
 			throws DbException;
 
+	/**
+	 * Records an ack for the given messages as having been sent to the given
+	 * contact.
+	 */
+	void setAckSent(Transaction txn, ContactId c, Collection<MessageId> acked)
+			throws DbException;
+
 	/**
 	 * Sets the cleanup timer duration for the given message. This does not
 	 * start the message's cleanup timer.
@@ -694,6 +737,13 @@ public interface DatabaseComponent extends TransactionManager {
 	void setMessageState(Transaction txn, MessageId m, MessageState state)
 			throws DbException;
 
+	/**
+	 * Records the given messages as having been sent to the given contact
+	 * over a transport with the given maximum latency.
+	 */
+	void setMessagesSent(Transaction txn, ContactId c,
+			Collection<MessageId> sent, long maxLatency) throws DbException;
+
 	/**
 	 * Adds dependencies for a message
 	 */

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

@@ -18,6 +18,10 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
  * submitted, tasks are not run concurrently, and submitting a task will never
  * block. Tasks must not run indefinitely. Tasks submitted during shutdown are
  * discarded.
+ * <p>
+ * It is not mandatory to use this executor for database tasks. The database
+ * can be accessed from any thread, but this executor's guarantee that tasks
+ * are run in the order they're submitted may be useful in some cases.
  */
 @Qualifier
 @Target({FIELD, METHOD, PARAMETER})

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

@@ -45,6 +45,9 @@ public class Transaction {
 	/**
 	 * Attaches an event to be broadcast when the transaction has been
 	 * committed. The event will be broadcast on the {@link EventExecutor}.
+	 * Events and {@link #attach(Runnable) tasks} are submitted to the
+	 * {@link EventExecutor} in the order they were attached to the
+	 * transaction.
 	 */
 	public void attach(Event e) {
 		if (actions == null) actions = new ArrayList<>();
@@ -54,6 +57,9 @@ public class Transaction {
 	/**
 	 * Attaches a task to be executed when the transaction has been
 	 * committed. The task will be run on the {@link EventExecutor}.
+	 * {@link #attach(Event) Events} and tasks are submitted to the
+	 * {@link EventExecutor} in the order they were attached to the
+	 * transaction.
 	 */
 	public void attach(Runnable r) {
 		if (actions == null) actions = new ArrayList<>();

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

@@ -1,51 +1,95 @@
 package org.briarproject.bramble.api.db;
 
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.ThreadSafe;
 
+/**
+ * An interface for managing database transactions.
+ * <p>
+ * Read-only transactions may access the database concurrently. Read-write
+ * transactions access the database exclusively, so starting a read-only or
+ * read-write transaction will block until there are no read-write
+ * transactions in progress.
+ * <p>
+ * Failing to {@link #endTransaction(Transaction) end} a transaction will
+ * prevent other callers from accessing the database, so it is recommended to
+ * use the {@link #transaction(boolean, DbRunnable)},
+ * {@link #transactionWithResult(boolean, DbCallable)} and
+ * {@link #transactionWithNullableResult(boolean, NullableDbCallable)} methods
+ * where possible, which handle committing or aborting the transaction on the
+ * caller's behalf.
+ * <p>
+ * Transactions are not reentrant, i.e. it is not permitted to start a
+ * transaction on a thread that already has a transaction in progress.
+ */
+@ThreadSafe
 @NotNullByDefault
 public interface TransactionManager {
 
 	/**
-	 * Starts a new transaction and returns an object representing it.
-	 * <p/>
-	 * This method acquires locks, so it must not be called while holding a
-	 * lock.
+	 * Starts a new transaction and returns an object representing it. This
+	 * method acquires the database lock, which is held until
+	 * {@link #endTransaction(Transaction)} is called.
 	 *
-	 * @param readOnly true if the transaction will only be used for reading.
+	 * @param readOnly True if the transaction will only be used for reading,
+	 * in which case the database lock can be shared with other read-only
+	 * transactions.
 	 */
 	Transaction startTransaction(boolean readOnly) throws DbException;
 
 	/**
 	 * Commits a transaction to the database.
+	 * {@link #endTransaction(Transaction)} must be called to release the
+	 * database lock.
 	 */
 	void commitTransaction(Transaction txn) throws DbException;
 
 	/**
-	 * Ends a transaction. If the transaction has not been committed,
-	 * it will be aborted. If the transaction has been committed,
-	 * any events attached to the transaction are broadcast.
-	 * The database lock will be released in either case.
+	 * Ends a transaction. If the transaction has not been committed by
+	 * calling {@link #commitTransaction(Transaction)}, it is aborted and the
+	 * database lock is released.
+	 * <p>
+	 * If the transaction has been committed, any
+	 * {@link Transaction#attach events} attached to the transaction are
+	 * broadcast and any {@link Transaction#attach(Runnable) tasks} attached
+	 * to the transaction are submitted to the {@link EventExecutor}. The
+	 * database lock is then released.
 	 */
 	void endTransaction(Transaction txn);
 
 	/**
-	 * Runs the given task within a transaction.
+	 * Runs the given task within a transaction. The database lock is held
+	 * while running the task.
+	 *
+	 * @param readOnly True if the transaction will only be used for reading,
+	 * in which case the database lock can be shared with other read-only
+	 * transactions.
 	 */
 	<E extends Exception> void transaction(boolean readOnly,
 			DbRunnable<E> task) throws DbException, E;
 
 	/**
 	 * Runs the given task within a transaction and returns the result of the
-	 * task.
+	 * task. The database lock is held while running the task.
+	 *
+	 * @param readOnly True if the transaction will only be used for reading,
+	 * in which case the database lock can be shared with other read-only
+	 * transactions.
 	 */
 	<R, E extends Exception> R transactionWithResult(boolean readOnly,
 			DbCallable<R, E> task) throws DbException, E;
 
 	/**
 	 * Runs the given task within a transaction and returns the result of the
-	 * task, which may be null.
+	 * task, which may be null. The database lock is held while running the
+	 * task.
+	 *
+	 * @param readOnly True if the transaction will only be used for reading,
+	 * in which case the database lock can be shared with other read-only
+	 * transactions.
 	 */
 	@Nullable
 	<R, E extends Exception> R transactionWithNullableResult(boolean readOnly,

bramble-api/src/main/java/org/briarproject/bramble/api/identity/AuthorId.java

@@ -21,9 +21,4 @@ public class AuthorId extends UniqueId {
 	public AuthorId(byte[] id) {
 		super(id);
 	}
-
-	@Override
-	public boolean equals(Object o) {
-		return o instanceof AuthorId && super.equals(o);
-	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxConstants.java

@@ -0,0 +1,68 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import java.util.List;
+
+import static java.util.Collections.singletonList;
+import static java.util.concurrent.TimeUnit.HOURS;
+import static org.briarproject.bramble.api.transport.TransportConstants.MAX_FRAME_LENGTH;
+import static org.briarproject.bramble.api.transport.TransportConstants.MAX_PAYLOAD_LENGTH;
+import static org.briarproject.bramble.api.transport.TransportConstants.STREAM_HEADER_LENGTH;
+import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENGTH;
+
+public interface MailboxConstants {
+
+	/**
+	 * The transport ID of the mailbox plugin.
+	 */
+	TransportId ID = new TransportId("org.briarproject.bramble.mailbox");
+
+	/**
+	 * Mailbox API versions that we support as a client. This is reported to our
+	 * contacts by {@link MailboxUpdateManager}.
+	 */
+	List<MailboxVersion> CLIENT_SUPPORTS = singletonList(
+			new MailboxVersion(1, 0));
+
+	/**
+	 * The constant returned by
+	 * {@link MailboxHelper#getHighestCommonMajorVersion(List, List)}
+	 * when the server is too old to support our major version.
+	 */
+	int API_SERVER_TOO_OLD = -1;
+
+	/**
+	 * The constant returned by
+	 * {@link MailboxHelper#getHighestCommonMajorVersion(List, List)}
+	 * when we as a client are too old to support the server's major version.
+	 */
+	int API_CLIENT_TOO_OLD = -2;
+
+	/**
+	 * The maximum length of a file that can be uploaded to or downloaded from
+	 * a mailbox.
+	 */
+	int MAX_FILE_BYTES = 1024 * 1024;
+
+	/**
+	 * The maximum length of the plaintext payload of a file, such that the
+	 * ciphertext is no more than {@link #MAX_FILE_BYTES}.
+	 */
+	int MAX_FILE_PAYLOAD_BYTES =
+			(MAX_FILE_BYTES - TAG_LENGTH - STREAM_HEADER_LENGTH)
+					/ MAX_FRAME_LENGTH * MAX_PAYLOAD_LENGTH;
+
+	/**
+	 * The number of connection failures
+	 * that indicate a problem with the mailbox.
+	 */
+	int PROBLEM_NUM_CONNECTION_FAILURES = 5;
+
+	/**
+	 * The time in milliseconds since the last connection success
+	 * that need to pass to indicates a problem with the mailbox.
+	 */
+	long PROBLEM_MS_SINCE_LAST_SUCCESS = HOURS.toMillis(1);
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxDirectory.java

@@ -0,0 +1,22 @@
+package org.briarproject.bramble.api.mailbox;
+
+import java.io.File;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Annotation for injecting the {@link File directory} where the Mailbox plugin
+ * should store its state.
+ */
+@Qualifier
+@Target({FIELD, METHOD, PARAMETER})
+@Retention(RUNTIME)
+public @interface MailboxDirectory {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxHelper.java

@@ -0,0 +1,35 @@
+package org.briarproject.bramble.api.mailbox;
+
+import java.util.List;
+import java.util.TreeSet;
+
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.API_CLIENT_TOO_OLD;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.API_SERVER_TOO_OLD;
+
+class MailboxHelper {
+
+	/**
+	 * Returns the highest major version that both client and server support
+	 * or {@link MailboxConstants#API_SERVER_TOO_OLD} if the server is too old
+	 * or {@link MailboxConstants#API_CLIENT_TOO_OLD} if the client is too old.
+	 */
+	static int getHighestCommonMajorVersion(
+			List<MailboxVersion> client, List<MailboxVersion> server) {
+		TreeSet<Integer> clientVersions = new TreeSet<>();
+		for (MailboxVersion version : client) {
+			clientVersions.add(version.getMajor());
+		}
+		TreeSet<Integer> serverVersions = new TreeSet<>();
+		for (MailboxVersion version : server) {
+			serverVersions.add(version.getMajor());
+		}
+		for (int clientVersion : clientVersions.descendingSet()) {
+			if (serverVersions.contains(clientVersion)) return clientVersion;
+		}
+		if (clientVersions.last() < serverVersions.last()) {
+			return API_CLIENT_TOO_OLD;
+		}
+		return API_SERVER_TOO_OLD;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxManager.java

@@ -2,6 +2,8 @@ package org.briarproject.bramble.api.mailbox;
 
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.mailbox.event.OwnMailboxConnectionStatusEvent;
 
 import javax.annotation.Nullable;
 
@@ -32,4 +34,23 @@ public interface MailboxManager {
 	 */
 	MailboxPairingTask startPairingTask(String qrCodePayload);
 
+	/**
+	 * Can be used by the UI to test the mailbox connection.
+	 *
+	 * @return true (success) or false (error).
+	 * A {@link OwnMailboxConnectionStatusEvent} might be broadcast with a new
+	 * {@link MailboxStatus}.
+	 */
+	boolean checkConnection();
+
+	/**
+	 * Unpairs the owner's mailbox and tries to wipe it.
+	 * As this makes a network call, it should be run on the {@link IoExecutor}.
+	 *
+	 * @return true if we could wipe the mailbox, false if we couldn't.
+	 * It is advised to inform the user to wipe the mailbox themselves,
+	 * if we failed to wipe it.
+	 */
+	@IoExecutor
+	boolean unPair() throws DbException;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxPairingState.java

@@ -1,59 +1,25 @@
 package org.briarproject.bramble.api.mailbox;
 
-import javax.annotation.Nullable;
-
 public abstract class MailboxPairingState {
 
-	/**
-	 * The QR code payload that was scanned by the user.
-	 * This is null if the code should not be re-used anymore in this state.
-	 */
-	@Nullable
-	public final String qrCodePayload;
-
-	MailboxPairingState(@Nullable String qrCodePayload) {
-		this.qrCodePayload = qrCodePayload;
-	}
-
 	public static class QrCodeReceived extends MailboxPairingState {
-		public QrCodeReceived(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class Pairing extends MailboxPairingState {
-		public Pairing(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class Paired extends MailboxPairingState {
-		public Paired() {
-			super(null);
-		}
 	}
 
 	public static class InvalidQrCode extends MailboxPairingState {
-		public InvalidQrCode() {
-			super(null);
-		}
 	}
 
 	public static class MailboxAlreadyPaired extends MailboxPairingState {
-		public MailboxAlreadyPaired() {
-			super(null);
-		}
 	}
 
 	public static class ConnectionError extends MailboxPairingState {
-		public ConnectionError(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class UnexpectedError extends MailboxPairingState {
-		public UnexpectedError(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxProperties.java

@@ -2,6 +2,9 @@ package org.briarproject.bramble.api.mailbox;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
+import java.util.List;
+
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
@@ -11,18 +14,48 @@ public class MailboxProperties {
 	private final String baseUrl;
 	private final MailboxAuthToken authToken;
 	private final boolean owner;
+	private final List<MailboxVersion> serverSupports;
+	@Nullable
+	private final MailboxFolderId inboxId; // Null for own mailbox
+	@Nullable
+	private final MailboxFolderId outboxId; // Null for own mailbox
 
+	/**
+	 * Constructor for properties used by the mailbox's owner.
+	 */
 	public MailboxProperties(String baseUrl, MailboxAuthToken authToken,
-			boolean owner) {
+			List<MailboxVersion> serverSupports) {
 		this.baseUrl = baseUrl;
 		this.authToken = authToken;
-		this.owner = owner;
+		this.owner = true;
+		this.serverSupports = serverSupports;
+		this.inboxId = null;
+		this.outboxId = null;
+	}
+
+	/**
+	 * Constructor for properties used by a contact of the mailbox's owner.
+	 */
+	public MailboxProperties(String baseUrl, MailboxAuthToken authToken,
+			List<MailboxVersion> serverSupports, MailboxFolderId inboxId,
+			MailboxFolderId outboxId) {
+		this.baseUrl = baseUrl;
+		this.authToken = authToken;
+		this.owner = false;
+		this.serverSupports = serverSupports;
+		this.inboxId = inboxId;
+		this.outboxId = outboxId;
 	}
 
 	public String getBaseUrl() {
 		return baseUrl;
 	}
 
+	public String getOnion() {
+		return baseUrl.replaceFirst("^http://", "")
+				.replaceFirst("\\.onion$", "");
+	}
+
 	public MailboxAuthToken getAuthToken() {
 		return authToken;
 	}
@@ -30,4 +63,18 @@ public class MailboxProperties {
 	public boolean isOwner() {
 		return owner;
 	}
+
+	public List<MailboxVersion> getServerSupports() {
+		return serverSupports;
+	}
+
+	@Nullable
+	public MailboxFolderId getInboxId() {
+		return inboxId;
+	}
+
+	@Nullable
+	public MailboxFolderId getOutboxId() {
+		return outboxId;
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxSettingsManager.java

@@ -1,15 +1,26 @@
 package org.briarproject.bramble.api.mailbox;
 
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
+import java.util.List;
+
 import javax.annotation.Nullable;
 
 @NotNullByDefault
 public interface MailboxSettingsManager {
 
+	/**
+	 * Registers a hook to be called when a mailbox has been paired or unpaired.
+	 * This method should be called before
+	 * {@link LifecycleManager#startServices(SecretKey)}.
+	 */
+	void registerMailboxHook(MailboxHook hook);
+
 	@Nullable
 	MailboxProperties getOwnMailboxProperties(Transaction txn)
 			throws DbException;
@@ -17,6 +28,8 @@ public interface MailboxSettingsManager {
 	void setOwnMailboxProperties(Transaction txn, MailboxProperties p)
 			throws DbException;
 
+	void removeOwnMailboxProperties(Transaction txn) throws DbException;
+
 	MailboxStatus getOwnMailboxStatus(Transaction txn) throws DbException;
 
 	void recordSuccessfulConnection(Transaction txn, long now)
@@ -30,4 +43,23 @@ public interface MailboxSettingsManager {
 
 	@Nullable
 	String getPendingUpload(Transaction txn, ContactId id) throws DbException;
+
+	interface MailboxHook {
+		/**
+		 * Called when Briar is paired with a mailbox
+		 *
+		 * @param txn A read-write transaction
+		 * @param ownOnion Our new mailbox's onion (56 base32 chars)
+		 */
+		void mailboxPaired(Transaction txn, String ownOnion,
+				List<MailboxVersion> serverSupports)
+				throws DbException;
+
+		/**
+		 * Called when the mailbox is unpaired
+		 *
+		 * @param txn A read-write transaction
+		 */
+		void mailboxUnpaired(Transaction txn) throws DbException;
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxStatus.java

@@ -2,20 +2,30 @@ package org.briarproject.bramble.api.mailbox;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
+import java.util.List;
+
 import javax.annotation.concurrent.Immutable;
 
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.CLIENT_SUPPORTS;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.PROBLEM_MS_SINCE_LAST_SUCCESS;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.PROBLEM_NUM_CONNECTION_FAILURES;
+import static org.briarproject.bramble.api.mailbox.MailboxHelper.getHighestCommonMajorVersion;
+
 @Immutable
 @NotNullByDefault
 public class MailboxStatus {
 
 	private final long lastAttempt, lastSuccess;
 	private final int attemptsSinceSuccess;
+	private final List<MailboxVersion> serverSupports;
 
 	public MailboxStatus(long lastAttempt, long lastSuccess,
-			int attemptsSinceSuccess) {
+			int attemptsSinceSuccess,
+			List<MailboxVersion> serverSupports) {
 		this.lastAttempt = lastAttempt;
 		this.lastSuccess = lastSuccess;
 		this.attemptsSinceSuccess = attemptsSinceSuccess;
+		this.serverSupports = serverSupports;
 	}
 
 	/**
@@ -56,4 +66,21 @@ public class MailboxStatus {
 	public int getAttemptsSinceSuccess() {
 		return attemptsSinceSuccess;
 	}
+
+	/**
+	 * @return true if this status indicates a problem with the mailbox.
+	 */
+	public boolean hasProblem(long now) {
+		return attemptsSinceSuccess >= PROBLEM_NUM_CONNECTION_FAILURES &&
+				(now - lastSuccess) >= PROBLEM_MS_SINCE_LAST_SUCCESS;
+	}
+
+	/**
+	 * @return a positive integer if the mailbox is compatible. Same result as
+	 * {@link MailboxHelper#getHighestCommonMajorVersion(List, List)}.
+	 */
+	public int getMailboxCompatibility() {
+		return getHighestCommonMajorVersion(CLIENT_SUPPORTS, serverSupports);
+	}
+
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxUpdate.java

@@ -0,0 +1,31 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class MailboxUpdate {
+	private final boolean hasMailbox;
+	private final List<MailboxVersion> clientSupports;
+
+	public MailboxUpdate(List<MailboxVersion> clientSupports) {
+		this(clientSupports, false);
+	}
+
+	MailboxUpdate(List<MailboxVersion> clientSupports, boolean hasMailbox) {
+		this.clientSupports = clientSupports;
+		this.hasMailbox = hasMailbox;
+	}
+
+	public List<MailboxVersion> getClientSupports() {
+		return clientSupports;
+	}
+
+	public boolean hasMailbox() {
+		return hasMailbox;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxUpdateManager.java

@@ -0,0 +1,72 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface MailboxUpdateManager {
+
+	/**
+	 * The unique ID of the mailbox update (properties) client.
+	 */
+	ClientId CLIENT_ID =
+			new ClientId("org.briarproject.bramble.mailbox.properties");
+
+	/**
+	 * The current major version of the mailbox update (properties) client.
+	 */
+	int MAJOR_VERSION = 2;
+
+	/**
+	 * The current minor version of the mailbox update (properties) client.
+	 */
+	int MINOR_VERSION = 0;
+
+	/**
+	 * The number of properties required for an update message with a mailbox.
+	 */
+	int PROP_COUNT = 4;
+
+	/**
+	 * The required properties of an update message with a mailbox.
+	 */
+	String PROP_KEY_ONION = "onion";
+	String PROP_KEY_AUTHTOKEN = "authToken";
+	String PROP_KEY_INBOXID = "inboxId";
+	String PROP_KEY_OUTBOXID = "outboxId";
+
+	/**
+	 * Length of the Onion property.
+	 */
+	int PROP_ONION_LENGTH = 56;
+
+	/**
+	 * Message metadata key for the version number of a local or remote update,
+	 * as a BDF long.
+	 */
+	String MSG_KEY_VERSION = "version";
+
+	/**
+	 * Message metadata key for whether an update is local or remote, as a BDF
+	 * boolean.
+	 */
+	String MSG_KEY_LOCAL = "local";
+
+	/**
+	 * Key in the client's local group for storing the clientSupports list that
+	 * was last sent out.
+	 */
+	String GROUP_KEY_SENT_CLIENT_SUPPORTS = "sentClientSupports";
+
+	MailboxUpdate getLocalUpdate(Transaction txn, ContactId c)
+			throws DbException;
+
+	@Nullable
+	MailboxUpdate getRemoteUpdate(Transaction txn, ContactId c)
+			throws DbException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxUpdateWithMailbox.java

@@ -0,0 +1,30 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class MailboxUpdateWithMailbox extends MailboxUpdate {
+
+	private final MailboxProperties properties;
+
+	public MailboxUpdateWithMailbox(List<MailboxVersion> clientSupports,
+			MailboxProperties properties) {
+		super(clientSupports, true);
+		if (properties.isOwner()) throw new IllegalArgumentException();
+		this.properties = properties;
+	}
+
+	public MailboxUpdateWithMailbox(MailboxUpdateWithMailbox o,
+			List<MailboxVersion> newClientSupports) {
+		this(newClientSupports, o.getMailboxProperties());
+	}
+
+	public MailboxProperties getMailboxProperties() {
+		return properties;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxVersion.java

@@ -0,0 +1,44 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class MailboxVersion implements Comparable<MailboxVersion> {
+
+	private final int major;
+	private final int minor;
+
+	public MailboxVersion(int major, int minor) {
+		this.major = major;
+		this.minor = minor;
+	}
+
+	public int getMajor() {
+		return major;
+	}
+
+	public int getMinor() {
+		return minor;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (o instanceof MailboxVersion) {
+			MailboxVersion v = (MailboxVersion) o;
+			return major == v.major && minor == v.minor;
+		}
+		return false;
+	}
+
+	@Override
+	public int compareTo(MailboxVersion v) {
+		int c = major - v.major;
+		if (c != 0) {
+			return c;
+		}
+		return minor - v.minor;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/event/MailboxProblemEvent.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.mailbox.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast by {@link MailboxSettingsManager} when
+ * recording a connection failure for own Mailbox
+ * that has persistent for long enough for the mailbox owner to become active
+ * and fix the problem with the mailbox.
+ */
+@Immutable
+@NotNullByDefault
+public class MailboxProblemEvent extends Event {
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/event/OwnMailboxConnectionStatusEvent.java

@@ -0,0 +1,27 @@
+package org.briarproject.bramble.api.mailbox.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.mailbox.MailboxStatus;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast by {@link MailboxSettingsManager} when
+ * recording the connection status of own Mailbox.
+ */
+@Immutable
+@NotNullByDefault
+public class OwnMailboxConnectionStatusEvent extends Event {
+
+	private final MailboxStatus status;
+
+	public OwnMailboxConnectionStatusEvent(MailboxStatus status) {
+		this.status = status;
+	}
+
+	public MailboxStatus getStatus() {
+		return status;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/event/RemoteMailboxUpdateEvent.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.mailbox.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when {@link MailboxUpdate} are received
+ * from a contact.
+ */
+@Immutable
+@NotNullByDefault
+public class RemoteMailboxUpdateEvent extends Event {
+
+	private final ContactId contactId;
+	private final MailboxUpdate mailboxUpdate;
+
+	public RemoteMailboxUpdateEvent(ContactId contactId,
+			MailboxUpdate mailboxUpdate) {
+		this.contactId = contactId;
+		this.mailboxUpdate = mailboxUpdate;
+	}
+
+	public ContactId getContact() {
+		return contactId;
+	}
+
+	public MailboxUpdate getMailboxUpdate() {
+		return mailboxUpdate;
+	}
+}

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

@@ -1,5 +1,7 @@
 package org.briarproject.bramble.api.plugin;
 
+import static java.util.concurrent.TimeUnit.SECONDS;
+
 public interface TorConstants {
 
 	TransportId ID = new TransportId("org.briarproject.bramble.tor");
@@ -10,8 +12,9 @@ public interface TorConstants {
 	int DEFAULT_SOCKS_PORT = 59050;
 	int DEFAULT_CONTROL_PORT = 59051;
 
-	int CONNECT_TO_PROXY_TIMEOUT = 5000; // Milliseconds
-	int EXTRA_SOCKET_TIMEOUT = 30000; // Milliseconds
+	int CONNECT_TO_PROXY_TIMEOUT = (int) SECONDS.toMillis(5);
+	int EXTRA_CONNECT_TIMEOUT = (int) SECONDS.toMillis(120);
+	int EXTRA_SOCKET_TIMEOUT = (int) SECONDS.toMillis(30);
 
 	// Local settings (not shared with contacts)
 	String PREF_TOR_NETWORK = "network2";

bramble-api/src/main/java/org/briarproject/bramble/api/record/RecordWriter.java

@@ -12,4 +12,6 @@ public interface RecordWriter {
 	void flush() throws IOException;
 
 	void close() throws IOException;
+
+	long getBytesWritten();
 }

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

@@ -0,0 +1,15 @@
+package org.briarproject.bramble.api.sync;
+
+import java.util.Collection;
+
+/**
+ * An interface for holding the IDs of messages sent and acked during an
+ * outgoing {@link SyncSession} so they can be recorded in the DB as sent
+ * or acked at some later time.
+ */
+public interface DeferredSendHandler {
+
+	void onAckSent(Collection<MessageId> acked);
+
+	void onMessageSent(MessageId sent);
+}

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

@@ -20,9 +20,4 @@ public class GroupId extends UniqueId {
 	public GroupId(byte[] id) {
 		super(id);
 	}
-
-	@Override
-	public boolean equals(Object o) {
-		return o instanceof GroupId && super.equals(o);
-	}
 }

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

@@ -27,9 +27,4 @@ public class MessageId extends UniqueId {
 	public MessageId(byte[] id) {
 		super(id);
 	}
-
-	@Override
-	public boolean equals(Object o) {
-		return o instanceof MessageId && super.equals(o);
-	}
 }

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

@@ -20,4 +20,6 @@ public interface SyncRecordWriter {
 	void writePriority(Priority p) throws IOException;
 
 	void flush() throws IOException;
+
+	long getBytesWritten();
 }

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.api.system;
 
+import org.briarproject.bramble.api.Cancellable;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.util.concurrent.Executor;
@@ -16,6 +17,8 @@ public interface TaskScheduler {
 	 * <p>
 	 * If the platform supports wake locks, a wake lock will be held while
 	 * submitting and running the task.
+	 *
+	 * @return A {@link Cancellable} for cancelling the task.
 	 */
 	Cancellable schedule(Runnable task, Executor executor, long delay,
 			TimeUnit unit);
@@ -27,17 +30,11 @@ public interface TaskScheduler {
 	 * <p>
 	 * If the platform supports wake locks, a wake lock will be held while
 	 * submitting and running the task.
+	 *
+	 * @return A {@link Cancellable} for cancelling all future executions of
+	 * the task.
 	 */
 	Cancellable scheduleWithFixedDelay(Runnable task, Executor executor,
 			long delay, long interval, TimeUnit unit);
 
-	interface Cancellable {
-
-		/**
-		 * Cancels the task if it has not already started running. If the task
-		 * is {@link #scheduleWithFixedDelay(Runnable, Executor, long, long, TimeUnit) periodic},
-		 * all future executions of the task are cancelled.
-		 */
-		void cancel();
-	}
 }

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

@@ -26,7 +26,7 @@ public class NetworkUtils {
 			// Despite what the docs say, the return value can be null
 			//noinspection ConstantConditions
 			return ifaces == null ? emptyList() : list(ifaces);
-		} catch (SocketException e) {
+		} catch (SocketException | NullPointerException e) {
 			logException(LOG, WARNING, e);
 			return emptyList();
 		}

bramble-api/src/test/java/org/briarproject/bramble/api/mailbox/MailboxHelperTest.java

@@ -0,0 +1,44 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.API_CLIENT_TOO_OLD;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.API_SERVER_TOO_OLD;
+import static org.briarproject.bramble.api.mailbox.MailboxHelper.getHighestCommonMajorVersion;
+import static org.junit.Assert.assertEquals;
+
+public class MailboxHelperTest {
+
+	private final Random random = new Random();
+
+	@Test
+	public void testGetHighestCommonMajorVersion() {
+		assertEquals(2, getHighestCommonMajorVersion(v(2), v(2)));
+		assertEquals(2, getHighestCommonMajorVersion(v(1, 2), v(2, 3, 4)));
+		assertEquals(2, getHighestCommonMajorVersion(v(2, 3, 4), v(2)));
+		assertEquals(2, getHighestCommonMajorVersion(v(2), v(2, 3, 4)));
+
+		assertEquals(API_CLIENT_TOO_OLD,
+				getHighestCommonMajorVersion(v(2), v(3, 4)));
+		assertEquals(API_CLIENT_TOO_OLD,
+				getHighestCommonMajorVersion(v(2), v(1, 3)));
+		assertEquals(API_SERVER_TOO_OLD,
+				getHighestCommonMajorVersion(v(3, 4, 5), v(2)));
+		assertEquals(API_SERVER_TOO_OLD,
+				getHighestCommonMajorVersion(v(1, 3), v(2)));
+	}
+
+	private List<MailboxVersion> v(int... ints) {
+		List<MailboxVersion> versions = new ArrayList<>(ints.length);
+		for (int v : ints) {
+			// minor versions should not matter
+			versions.add(new MailboxVersion(v, random.nextInt(42)));
+		}
+		return versions;
+	}
+
+}

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

@@ -1,17 +1,46 @@
 package org.briarproject.bramble.test;
 
-import java.lang.Thread.UncaughtExceptionHandler;
+import org.junit.After;
+import org.junit.Before;
 
-import static org.junit.Assert.fail;
+import java.lang.Thread.UncaughtExceptionHandler;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 
 public abstract class BrambleTestCase {
 
+	private static final Logger LOG =
+			getLogger(BrambleTestCase.class.getName());
+
+	@Nullable
+	protected volatile Throwable exceptionInBackgroundThread = null;
+
 	public BrambleTestCase() {
 		// Ensure exceptions thrown on worker threads cause tests to fail
 		UncaughtExceptionHandler fail = (thread, throwable) -> {
-			throwable.printStackTrace();
-			fail();
+			LOG.log(WARNING, "Caught unhandled exception", throwable);
+			exceptionInBackgroundThread = throwable;
 		};
 		Thread.setDefaultUncaughtExceptionHandler(fail);
 	}
+
+	@Before
+	public void beforeBrambleTestCase() {
+		exceptionInBackgroundThread = null;
+	}
+
+	@After
+	public void afterBrambleTestCase() {
+		Throwable thrown = exceptionInBackgroundThread;
+		if (thrown != null) {
+			LOG.log(WARNING,
+					"Background thread has thrown an exception unexpectedly",
+					thrown);
+			throw new AssertionError(thrown);
+		}
+	}
 }

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

@@ -12,10 +12,20 @@ import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.SignaturePrivateKey;
 import org.briarproject.bramble.api.crypto.SignaturePublicKey;
+import org.briarproject.bramble.api.db.CommitAction;
+import org.briarproject.bramble.api.db.EventAction;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
 import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
+import org.briarproject.bramble.api.mailbox.MailboxFolderId;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateWithMailbox;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.sync.ClientId;
@@ -30,6 +40,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -39,6 +50,9 @@ import java.util.Map;
 import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import javax.annotation.Nullable;
+import javax.crypto.Cipher;
+
 import static java.util.Arrays.asList;
 import static org.briarproject.bramble.api.crypto.CryptoConstants.MAX_AGREEMENT_PUBLIC_KEY_BYTES;
 import static org.briarproject.bramble.api.crypto.CryptoConstants.MAX_SIGNATURE_PUBLIC_KEY_BYTES;
@@ -214,6 +228,19 @@ public class TestUtils {
 				getAgreementPublicKey(), verified);
 	}
 
+	public static MailboxProperties getMailboxProperties(boolean owner,
+			List<MailboxVersion> serverSupports) {
+		String baseUrl = "http://" + getRandomString(56) + ".onion"; // TODO
+		MailboxAuthToken authToken = new MailboxAuthToken(getRandomId());
+		if (owner) {
+			return new MailboxProperties(baseUrl, authToken, serverSupports);
+		}
+		MailboxFolderId inboxId = new MailboxFolderId(getRandomId());
+		MailboxFolderId outboxId = new MailboxFolderId(getRandomId());
+		return new MailboxProperties(baseUrl, authToken, serverSupports,
+				inboxId, outboxId);
+	}
+
 	public static void writeBytes(File file, byte[] bytes)
 			throws IOException {
 		FileOutputStream outputStream = new FileOutputStream(file);
@@ -266,9 +293,57 @@ public class TestUtils {
 		return Math.sqrt(getVariance(samples));
 	}
 
-	public static boolean isOptionalTestEnabled(Class testClass) {
+	public static boolean isOptionalTestEnabled(Class<?> testClass) {
 		String optionalTests = System.getenv("OPTIONAL_TESTS");
 		return optionalTests != null &&
 				asList(optionalTests.split(",")).contains(testClass.getName());
 	}
+
+	public static boolean mailboxUpdateEqual(@Nullable MailboxUpdate a,
+			@Nullable MailboxUpdate b) {
+		if (a == null || b == null) {
+			return a == b;
+		}
+		if (!a.hasMailbox() && !b.hasMailbox()) {
+			return a.getClientSupports().equals(b.getClientSupports());
+		} else if (a.hasMailbox() && b.hasMailbox()) {
+			MailboxUpdateWithMailbox am = (MailboxUpdateWithMailbox) a;
+			MailboxUpdateWithMailbox bm = (MailboxUpdateWithMailbox) b;
+			return am.getClientSupports().equals(bm.getClientSupports()) &&
+					mailboxPropertiesEqual(am.getMailboxProperties(),
+							bm.getMailboxProperties());
+		}
+		return false;
+	}
+
+	public static boolean mailboxPropertiesEqual(@Nullable MailboxProperties a,
+			@Nullable MailboxProperties b) {
+		if (a == null || b == null) {
+			return a == b;
+		}
+		return a.getOnion().equals(b.getOnion()) &&
+				a.getAuthToken().equals(b.getAuthToken()) &&
+				a.isOwner() == b.isOwner() &&
+				a.getServerSupports().equals(b.getServerSupports());
+	}
+
+	public static boolean hasEvent(Transaction txn,
+			Class<? extends Event> eventClass) {
+		for (CommitAction action : txn.getActions()) {
+			if (action instanceof EventAction) {
+				Event event = ((EventAction) action).getEvent();
+				if (eventClass.isInstance(event)) return true;
+			}
+		}
+		return false;
+	}
+
+	public static boolean isCryptoStrengthUnlimited() {
+		try {
+			return Cipher.getMaxAllowedKeyLength("AES/CBC/PKCS5Padding")
+					== Integer.MAX_VALUE;
+		} catch (NoSuchAlgorithmException e) {
+			throw new AssertionError();
+		}
+	}
 }

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

@@ -0,0 +1,36 @@
+package org.briarproject.bramble.test;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.fail;
+
+public class ThreadExceptionTest extends BrambleTestCase {
+
+	@Test(expected = AssertionError.class)
+	public void testAssertionErrorMakesTestCaseFail() {
+		// This is what BrambleTestCase does, too:
+		fail();
+	}
+
+	@Test
+	public void testExceptionInThreadMakesTestCaseFail() {
+		Thread t = new Thread(() -> {
+			System.out.println("thread before exception");
+			throw new RuntimeException("boom");
+		});
+
+		t.start();
+		try {
+			t.join();
+			System.out.println("joined thread");
+		} catch (InterruptedException e) {
+			System.out.println("interrupted while joining thread");
+			fail();
+		}
+
+		assertNotNull(exceptionInBackgroundThread);
+		exceptionInBackgroundThread = null;
+	}
+
+}

bramble-api/witness.gradle

@@ -1,6 +1,7 @@
 dependencyVerification {
     verify = [
         'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
+        'com.fasterxml.jackson.core:jackson-annotations:2.13.0:jackson-annotations-2.13.0.jar:81f9724d8843e8b08f8f6c0609e7a2b030d00c34861c4ac7e2099a7235047d6f',
         'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.dagger:dagger:2.33:dagger-2.33.jar:d8798c5b8cf6b125234e33af5c6293bb9f2208ce29b57924c35b8c0be7b6bdcb',

bramble-core/build.gradle

@@ -16,7 +16,7 @@ dependencies {
 	implementation 'org.bitlet:weupnp:0.1.4'
 	implementation 'net.i2p.crypto:eddsa:0.2.0'
 	implementation 'org.whispersystems:curve25519-java:0.5.0'
-	implementation 'org.briarproject:jtorctl:0.3'
+	implementation 'org.briarproject:jtorctl:0.4'
 
 	//noinspection GradleDependency
 	implementation "com.squareup.okhttp3:okhttp:$okhttp_version"

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

@@ -6,6 +6,7 @@ import org.briarproject.bramble.crypto.CryptoExecutorModule;
 import org.briarproject.bramble.db.DatabaseExecutorModule;
 import org.briarproject.bramble.identity.IdentityModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
+import org.briarproject.bramble.mailbox.MailboxModule;
 import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.rendezvous.RendezvousModule;
@@ -28,6 +29,8 @@ public interface BrambleCoreEagerSingletons {
 
 	void inject(LifecycleModule.EagerSingletons init);
 
+	void inject(MailboxModule.EagerSingletons init);
+
 	void inject(PluginModule.EagerSingletons init);
 
 	void inject(PropertiesModule.EagerSingletons init);
@@ -51,6 +54,7 @@ public interface BrambleCoreEagerSingletons {
 			c.inject(new DatabaseExecutorModule.EagerSingletons());
 			c.inject(new IdentityModule.EagerSingletons());
 			c.inject(new LifecycleModule.EagerSingletons());
+			c.inject(new MailboxModule.EagerSingletons());
 			c.inject(new RendezvousModule.EagerSingletons());
 			c.inject(new PluginModule.EagerSingletons());
 			c.inject(new PropertiesModule.EagerSingletons());

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

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.client;
 
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.client.ClientHelper;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
@@ -22,6 +23,12 @@ import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorFactory;
+import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
+import org.briarproject.bramble.api.mailbox.MailboxFolderId;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateWithMailbox;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.properties.TransportProperties;
@@ -29,13 +36,16 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.util.Base32;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.security.GeneralSecurityException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 
@@ -46,6 +56,12 @@ import static org.briarproject.bramble.api.client.ContactGroupConstants.GROUP_KE
 import static org.briarproject.bramble.api.identity.Author.FORMAT_VERSION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_COUNT;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_KEY_AUTHTOKEN;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_KEY_INBOXID;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_KEY_ONION;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_KEY_OUTBOXID;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.PROP_ONION_LENGTH;
 import static org.briarproject.bramble.api.properties.TransportPropertyConstants.MAX_PROPERTIES_PER_TRANSPORT;
 import static org.briarproject.bramble.api.properties.TransportPropertyConstants.MAX_PROPERTY_LENGTH;
 import static org.briarproject.bramble.util.ValidationUtils.checkLength;
@@ -399,6 +415,69 @@ class ClientHelperImpl implements ClientHelper {
 		return tpMap;
 	}
 
+	@Override
+	public MailboxUpdate parseAndValidateMailboxUpdate(BdfList clientSupports,
+			BdfList serverSupports, BdfDictionary properties)
+			throws FormatException {
+		List<MailboxVersion> clientSupportsList =
+				parseMailboxVersionList(clientSupports);
+		List<MailboxVersion> serverSupportsList =
+				parseMailboxVersionList(serverSupports);
+
+		// We must always learn what Mailbox API version(s) the client supports
+		if (clientSupports.isEmpty()) {
+			throw new FormatException();
+		}
+		if (properties.isEmpty()) {
+			// No mailbox -- cannot claim to support any API versions!
+			if (!serverSupports.isEmpty()) {
+				throw new FormatException();
+			}
+			return new MailboxUpdate(clientSupportsList);
+		}
+		// Mailbox must be accompanied by the Mailbox API version(s) it supports
+		if (serverSupports.isEmpty()) {
+			throw new FormatException();
+		}
+		// Accepting more props than we need, for forward compatibility
+		if (properties.size() < PROP_COUNT) {
+			throw new FormatException();
+		}
+		String onion = properties.getString(PROP_KEY_ONION);
+		checkLength(onion, PROP_ONION_LENGTH);
+		try {
+			Base32.decode(onion, true);
+		} catch (IllegalArgumentException e) {
+			throw new FormatException();
+		}
+		byte[] authToken = properties.getRaw(PROP_KEY_AUTHTOKEN);
+		checkLength(authToken, UniqueId.LENGTH);
+		byte[] inboxId = properties.getRaw(PROP_KEY_INBOXID);
+		checkLength(inboxId, UniqueId.LENGTH);
+		byte[] outboxId = properties.getRaw(PROP_KEY_OUTBOXID);
+		checkLength(outboxId, UniqueId.LENGTH);
+		String baseUrl = "http://" + onion + ".onion"; // TODO
+		MailboxProperties props = new MailboxProperties(baseUrl,
+				new MailboxAuthToken(authToken), serverSupportsList,
+				new MailboxFolderId(inboxId), new MailboxFolderId(outboxId));
+		return new MailboxUpdateWithMailbox(clientSupportsList, props);
+	}
+
+	@Override
+	public List<MailboxVersion> parseMailboxVersionList(BdfList bdfList)
+			throws FormatException {
+		List<MailboxVersion> list = new ArrayList<>();
+		for (int i = 0; i < bdfList.size(); i++) {
+			BdfList element = bdfList.getList(i);
+			if (element.size() != 2) {
+				throw new FormatException();
+			}
+			list.add(new MailboxVersion(element.getLong(0).intValue(),
+					element.getLong(1).intValue()));
+		}
+		return list;
+	}
+
 	@Override
 	public ContactId getContactId(Transaction txn, GroupId contactGroupId)
 			throws DbException {

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

@@ -54,7 +54,7 @@ abstract class Connection {
 		}
 	}
 
-	private byte[] readTag(InputStream in) throws IOException {
+	byte[] readTag(InputStream in) throws IOException {
 		byte[] tag = new byte[TAG_LENGTH];
 		read(in, tag);
 		return tag;

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

@@ -67,7 +67,15 @@ class ConnectionManagerImpl implements ConnectionManager {
 			TransportConnectionReader r) {
 		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
 				connectionRegistry, streamReaderFactory, streamWriterFactory,
-				syncSessionFactory, transportPropertyManager, t, r));
+				syncSessionFactory, transportPropertyManager, t, r, null));
+	}
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			TransportConnectionReader r, TagController c) {
+		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, t, r, c));
 	}
 
 	@Override

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

@@ -1,7 +1,9 @@
 package org.briarproject.bramble.connection;
 
+import org.briarproject.bramble.api.connection.ConnectionManager.TagController;
 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;
@@ -15,6 +17,8 @@ import org.briarproject.bramble.api.transport.StreamWriterFactory;
 
 import java.io.IOException;
 
+import javax.annotation.Nullable;
+
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
@@ -23,6 +27,8 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 
 	private final TransportId transportId;
 	private final TransportConnectionReader reader;
+	@Nullable
+	private final TagController tagController;
 
 	IncomingSimplexSyncConnection(KeyManager keyManager,
 			ConnectionRegistry connectionRegistry,
@@ -30,33 +36,50 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 			StreamWriterFactory streamWriterFactory,
 			SyncSessionFactory syncSessionFactory,
 			TransportPropertyManager transportPropertyManager,
-			TransportId transportId, TransportConnectionReader reader) {
+			TransportId transportId,
+			TransportConnectionReader reader,
+			@Nullable TagController tagController) {
 		super(keyManager, connectionRegistry, streamReaderFactory,
 				streamWriterFactory, syncSessionFactory,
 				transportPropertyManager);
 		this.transportId = transportId;
 		this.reader = reader;
+		this.tagController = tagController;
 	}
 
 	@Override
 	public void run() {
 		// Read and recognise the tag
-		StreamContext ctx = recogniseTag(reader, transportId);
+		byte[] tag;
+		StreamContext ctx;
+		try {
+			tag = readTag(reader.getInputStream());
+			// If we have a tag controller, defer marking the tag as recognised
+			if (tagController == null) {
+				ctx = keyManager.getStreamContext(transportId, tag);
+			} else {
+				ctx = keyManager.getStreamContextOnly(transportId, tag);
+			}
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			return;
+		}
 		if (ctx == null) {
 			LOG.info("Unrecognised tag");
-			onError(false);
+			onError();
 			return;
 		}
 		ContactId contactId = ctx.getContactId();
 		if (contactId == null) {
 			LOG.warning("Received rendezvous stream, expected contact");
-			onError(true);
+			onError(tag);
 			return;
 		}
 		if (ctx.isHandshakeMode()) {
 			// TODO: Support handshake mode for contacts
 			LOG.warning("Received handshake tag, expected rotation mode");
-			onError(true);
+			onError(tag);
 			return;
 		}
 		try {
@@ -65,15 +88,33 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 					LOG.info("Ignoring priority for simplex connection");
 			// Create and run the incoming session
 			createIncomingSession(ctx, reader, handler).run();
+			// Success
+			markTagAsRecognisedIfRequired(false, tag);
 			reader.dispose(false, true);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
-			onError(true);
+			onError(tag);
 		}
 	}
 
-	private void onError(boolean recognised) {
-		disposeOnError(reader, recognised);
+	private void onError() {
+		disposeOnError(reader, false);
+	}
+
+	private void onError(byte[] tag) {
+		markTagAsRecognisedIfRequired(true, tag);
+		disposeOnError(reader, true);
+	}
+
+	private void markTagAsRecognisedIfRequired(boolean exception, byte[] tag) {
+		if (tagController != null &&
+				tagController.shouldMarkTagAsRecognised(exception)) {
+			try {
+				keyManager.markTagAsRecognised(transportId, tag);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		}
 	}
 }
 

bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java

@@ -8,6 +8,7 @@ import org.bouncycastle.crypto.CryptoException;
 import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.digests.Blake2bDigest;
 import org.bouncycastle.crypto.digests.SHA3Digest;
+import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.crypto.AgreementPrivateKey;
 import org.briarproject.bramble.api.crypto.AgreementPublicKey;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
@@ -41,6 +42,7 @@ import javax.inject.Inject;
 
 import static java.lang.System.arraycopy;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.crypto.CryptoConstants.KEY_TYPE_AGREEMENT;
 import static org.briarproject.bramble.api.crypto.CryptoConstants.KEY_TYPE_SIGNATURE;
 import static org.briarproject.bramble.api.crypto.DecryptionResult.INVALID_CIPHERTEXT;
@@ -54,7 +56,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class CryptoComponentImpl implements CryptoComponent {
 
 	private static final Logger LOG =
-			Logger.getLogger(CryptoComponentImpl.class.getName());
+			getLogger(CryptoComponentImpl.class.getName());
 
 	private static final int SIGNATURE_KEY_PAIR_BITS = 256;
 	private static final int STORAGE_IV_BYTES = 24; // 196 bits
@@ -128,6 +130,13 @@ class CryptoComponentImpl implements CryptoComponent {
 		}
 	}
 
+	@Override
+	public UniqueId generateUniqueId() {
+		byte[] b = new byte[UniqueId.LENGTH];
+		secureRandom.nextBytes(b);
+		return new UniqueId(b);
+	}
+
 	@Override
 	public SecretKey generateSecretKey() {
 		byte[] b = new byte[SecretKey.LENGTH];
@@ -449,7 +458,7 @@ class CryptoComponentImpl implements CryptoComponent {
 	}
 
 	@Override
-	public String encodeOnionAddress(byte[] publicKey) {
+	public String encodeOnion(byte[] publicKey) {
 		Digest digest = new SHA3Digest(256);
 		byte[] label = ".onion checksum".getBytes(Charset.forName("US-ASCII"));
 		digest.update(label, 0, label.length);

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

@@ -406,6 +406,12 @@ interface Database<T> {
 	Collection<MessageId> getMessageIds(T txn, GroupId g, Metadata query)
 			throws DbException;
 
+	/**
+	 * Returns the length of the given message in bytes, including the
+	 * message header.
+	 */
+	int getMessageLength(T txn, MessageId m) throws DbException;
+
 	/**
 	 * Returns the metadata for all delivered messages in the given group.
 	 * <p/>
@@ -496,7 +502,8 @@ interface Database<T> {
 
 	/**
 	 * Returns the IDs of some messages that are eligible to be sent to the
-	 * given contact, up to the given total length.
+	 * given contact. The total length of the messages including record headers
+	 * will be no more than the given capacity.
 	 * <p/>
 	 * Unlike {@link #getUnackedMessagesToSend(Object, ContactId)} this method
 	 * does not return messages that have already been sent unless they are
@@ -504,20 +511,20 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<MessageId> getMessagesToSend(T txn, ContactId c, int maxLength,
+	Collection<MessageId> getMessagesToSend(T txn, ContactId c, long capacity,
 			long maxLatency) throws DbException;
 
 	/**
 	 * Returns the IDs of all messages that are eligible to be sent to the
-	 * given contact, together with their raw lengths.
+	 * given contact.
 	 * <p/>
-	 * Unlike {@link #getMessagesToSend(Object, ContactId, int, long)} this
+	 * Unlike {@link #getMessagesToSend(Object, ContactId, long, long)} this
 	 * method may return messages that have already been sent and are not yet
 	 * due for retransmission.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, Integer> getUnackedMessagesToSend(T txn, ContactId c)
+	Collection<MessageId> getUnackedMessagesToSend(T txn, ContactId c)
 			throws DbException;
 
 	/**
@@ -598,13 +605,14 @@ interface Database<T> {
 
 	/**
 	 * Returns the IDs of some messages that are eligible to be sent to the
-	 * given contact and have been requested by the contact, up to the given
-	 * total length.
+	 * given contact and have been requested by the contact. The total length
+	 * of the messages including record headers will be no more than the given
+	 * capacity.
 	 * <p/>
 	 * Read-only.
 	 */
 	Collection<MessageId> getRequestedMessagesToSend(T txn, ContactId c,
-			int maxLength, long maxLatency) throws DbException;
+			long capacity, long maxLatency) throws DbException;
 
 	/**
 	 * Returns all settings in the given namespace.
@@ -758,9 +766,10 @@ interface Database<T> {
 	void resetExpiryTime(T txn, ContactId c, MessageId m) throws DbException;
 
 	/**
-	 * Resets the transmission count, expiry time and ETA of all messages that
-	 * are eligible to be sent to the given contact. This includes messages that
-	 * have already been sent and are not yet due for retransmission.
+	 * Resets the transmission count, expiry time and max latency of all
+	 * messages that are eligible to be sent to the given contact. This includes
+	 * messages that have already been sent and are not yet due for
+	 * retransmission.
 	 */
 	void resetUnackedMessagesToSend(T txn, ContactId c) throws DbException;
 
@@ -848,11 +857,13 @@ interface Database<T> {
 	void stopCleanupTimer(T txn, MessageId m) throws DbException;
 
 	/**
-	 * Updates the transmission count, expiry time and estimated time of arrival
-	 * of the given message with respect to the given contact, using the latency
-	 * of the transport over which it was sent.
+	 * Updates the transmission count, expiry time and max latency of the given
+	 * message with respect to the given contact.
+	 *
+	 * @param maxLatency latency of the transport over which the message was
+	 * sent.
 	 */
-	void updateExpiryTimeAndEta(T txn, ContactId c, MessageId m,
+	void updateRetransmissionData(T txn, ContactId c, MessageId m,
 			long maxLatency) throws DbException;
 
 	/**

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

@@ -75,7 +75,6 @@ import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Executor;
@@ -87,6 +86,7 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+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.sync.Group.Visibility.INVISIBLE;
@@ -424,53 +424,27 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	@Nullable
 	@Override
 	public Collection<Message> generateBatch(Transaction transaction,
-			ContactId c, int maxLength, long maxLatency) throws DbException {
+			ContactId c, long capacity, long maxLatency) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
 		Collection<MessageId> ids =
-				db.getMessagesToSend(txn, c, maxLength, maxLatency);
+				db.getMessagesToSend(txn, c, capacity, maxLatency);
+		if (ids.isEmpty()) return null;
 		long totalLength = 0;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
 			Message message = db.getMessage(txn, m);
 			totalLength += message.getRawLength();
 			messages.add(message);
-			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
+			db.updateRetransmissionData(txn, c, m, maxLatency);
 		}
-		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
 		transaction.attach(new MessagesSentEvent(c, ids, totalLength));
 		return messages;
 	}
 
-	@Override
-	public Collection<Message> generateBatch(Transaction transaction,
-			ContactId c, Collection<MessageId> ids, long maxLatency)
-			throws DbException {
-		if (transaction.isReadOnly()) throw new IllegalArgumentException();
-		T txn = unbox(transaction);
-		if (!db.containsContact(txn, c))
-			throw new NoSuchContactException();
-		long totalLength = 0;
-		List<Message> messages = new ArrayList<>(ids.size());
-		List<MessageId> sentIds = new ArrayList<>(ids.size());
-		for (MessageId m : ids) {
-			if (db.containsVisibleMessage(txn, c, m)) {
-				Message message = db.getMessage(txn, m);
-				totalLength += message.getRawLength();
-				messages.add(message);
-				sentIds.add(m);
-				db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
-			}
-		}
-		if (messages.isEmpty()) return messages;
-		db.lowerRequestedFlag(txn, c, sentIds);
-		transaction.attach(new MessagesSentEvent(c, sentIds, totalLength));
-		return messages;
-	}
-
 	@Nullable
 	@Override
 	public Offer generateOffer(Transaction transaction, ContactId c,
@@ -483,7 +457,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 				db.getMessagesToOffer(txn, c, maxMessages, maxLatency);
 		if (ids.isEmpty()) return null;
 		for (MessageId m : ids)
-			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
+			db.updateRetransmissionData(txn, c, m, maxLatency);
 		return new Offer(ids);
 	}
 
@@ -505,22 +479,22 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	@Nullable
 	@Override
 	public Collection<Message> generateRequestedBatch(Transaction transaction,
-			ContactId c, int maxLength, long maxLatency) throws DbException {
+			ContactId c, long capacity, long maxLatency) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
 		Collection<MessageId> ids =
-				db.getRequestedMessagesToSend(txn, c, maxLength, maxLatency);
+				db.getRequestedMessagesToSend(txn, c, capacity, maxLatency);
+		if (ids.isEmpty()) return null;
 		long totalLength = 0;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
 			Message message = db.getMessage(txn, m);
 			totalLength += message.getRawLength();
 			messages.add(message);
-			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
+			db.updateRetransmissionData(txn, c, m, maxLatency);
 		}
-		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
 		transaction.attach(new MessagesSentEvent(c, ids, totalLength));
 		return messages;
@@ -635,6 +609,24 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getMessageIds(txn, g, query);
 	}
 
+	@Override
+	public Collection<MessageId> getMessagesToAck(Transaction transaction,
+			ContactId c, int maxMessages) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		return db.getMessagesToAck(txn, c, maxMessages);
+	}
+
+	@Override
+	public Collection<MessageId> getMessagesToSend(Transaction transaction,
+			ContactId c, long capacity, long maxLatency) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		return db.getMessagesToSend(txn, c, capacity, maxLatency);
+	}
+
 	@Override
 	public Collection<MessageId> getMessagesToValidate(Transaction transaction)
 			throws DbException {
@@ -740,10 +732,29 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return status;
 	}
 
+	@Nullable
 	@Override
-	public Map<MessageId, Integer> getUnackedMessagesToSend(
-			Transaction transaction,
-			ContactId c) throws DbException {
+	public Message getMessageToSend(Transaction transaction, ContactId c,
+			MessageId m, long maxLatency, boolean markAsSent)
+			throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		if (!db.containsVisibleMessage(txn, c, m)) return null;
+		Message message = db.getMessage(txn, m);
+		if (markAsSent) {
+			db.updateRetransmissionData(txn, c, m, maxLatency);
+			db.lowerRequestedFlag(txn, c, singletonList(m));
+			transaction.attach(new MessagesSentEvent(c, singletonList(m),
+					message.getRawLength()));
+		}
+		return message;
+	}
+
+	@Override
+	public Collection<MessageId> getUnackedMessagesToSend(
+			Transaction transaction, ContactId c) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
@@ -1069,6 +1080,20 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		db.removeTransportKeys(txn, t, k);
 	}
 
+	@Override
+	public void setAckSent(Transaction transaction, ContactId c,
+			Collection<MessageId> acked) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		List<MessageId> visible = new ArrayList<>(acked.size());
+		for (MessageId m : acked) {
+			if (db.containsVisibleMessage(txn, c, m)) visible.add(m);
+		}
+		db.lowerAckFlag(txn, c, visible);
+	}
+
 	@Override
 	public void setCleanupTimerDuration(Transaction transaction, MessageId m,
 			long duration) throws DbException {
@@ -1115,7 +1140,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		if (old == INVISIBLE) db.addGroupVisibility(txn, c, g, v == SHARED);
 		else if (v == INVISIBLE) db.removeGroupVisibility(txn, c, g);
 		else db.setGroupVisibility(txn, c, g, v == SHARED);
-		List<ContactId> affected = Collections.singletonList(c);
+		List<ContactId> affected = singletonList(c);
 		transaction.attach(new GroupVisibilityUpdatedEvent(affected));
 	}
 
@@ -1163,6 +1188,28 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		transaction.attach(new MessageStateChangedEvent(m, false, state));
 	}
 
+	@Override
+	public void setMessagesSent(Transaction transaction, ContactId c,
+			Collection<MessageId> sent, long maxLatency) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		long totalLength = 0;
+		List<MessageId> visible = new ArrayList<>(sent.size());
+		for (MessageId m : sent) {
+			if (db.containsVisibleMessage(txn, c, m)) {
+				visible.add(m);
+				totalLength += db.getMessageLength(txn, m);
+				db.updateRetransmissionData(txn, c, m, maxLatency);
+			}
+		}
+		db.lowerRequestedFlag(txn, c, visible);
+		if (!visible.isEmpty()) {
+			transaction.attach(new MessagesSentEvent(c, visible, totalLength));
+		}
+	}
+
 	@Override
 	public void addMessageDependencies(Transaction transaction,
 			Message dependent, Collection<MessageId> dependencies)

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

@@ -2,8 +2,6 @@ package org.briarproject.bramble.db;
 
 import org.briarproject.bramble.api.settings.Settings;
 
-import static java.util.concurrent.TimeUnit.DAYS;
-
 interface DatabaseConstants {
 
 	/**
@@ -25,19 +23,6 @@ interface DatabaseConstants {
 	 */
 	String SCHEMA_VERSION_KEY = "schemaVersion";
 
-	/**
-	 * The {@link Settings} key under which the time of the last database
-	 * compaction is stored.
-	 */
-	String LAST_COMPACTED_KEY = "lastCompacted";
-
-	/**
-	 * The maximum time between database compactions in milliseconds. When the
-	 * database is opened it will be compacted if more than this amount of time
-	 * has passed since the last compaction.
-	 */
-	long MAX_COMPACTION_INTERVAL_MS = DAYS.toMillis(30);
-
 	/**
 	 * The {@link Settings} key under which the flag is stored indicating
 	 * whether the database is marked as dirty.

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

@@ -3,15 +3,16 @@ package org.briarproject.bramble.db;
 class DatabaseTypes {
 
 	private final String hashType, secretType, binaryType;
-	private final String counterType, stringType;
+	private final String counterType, stringType, schemaQuery;
 
-	public DatabaseTypes(String hashType, String secretType, String binaryType,
-			String counterType, String stringType) {
+	DatabaseTypes(String hashType, String secretType, String binaryType,
+			String counterType, String stringType, String schemaQuery) {
 		this.hashType = hashType;
 		this.secretType = secretType;
 		this.binaryType = binaryType;
 		this.counterType = counterType;
 		this.stringType = stringType;
+		this.schemaQuery = schemaQuery;
 	}
 
 	/**
@@ -31,4 +32,8 @@ class DatabaseTypes {
 		s = s.replaceAll("_STRING", stringType);
 		return s;
 	}
+
+	String getSchemaQuery() {
+		return schemaQuery;
+	}
 }

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

@@ -41,8 +41,9 @@ class H2Database extends JdbcDatabase {
 	private static final String BINARY_TYPE = "BINARY";
 	private static final String COUNTER_TYPE = "INT NOT NULL AUTO_INCREMENT";
 	private static final String STRING_TYPE = "VARCHAR";
+	private static final String SCHEMA_QUERY = "SHOW TABLES";
 	private static final DatabaseTypes dbTypes = new DatabaseTypes(HASH_TYPE,
-			SECRET_TYPE, BINARY_TYPE, COUNTER_TYPE, STRING_TYPE);
+			SECRET_TYPE, BINARY_TYPE, COUNTER_TYPE, STRING_TYPE, SCHEMA_QUERY);
 
 	private final DatabaseConfig config;
 	private final String url;
@@ -85,12 +86,17 @@ class H2Database extends JdbcDatabase {
 	public void close() throws DbException {
 		// H2 will close the database when the last connection closes
 		Connection c = null;
+		Statement s = null;
 		try {
 			c = createConnection();
-			super.closeAllConnections();
+			closeAllConnections();
 			setDirty(c, false);
+			s = c.createStatement();
+			s.execute("SHUTDOWN COMPACT");
+			s.close();
 			c.close();
 		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
 			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}

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

@@ -41,8 +41,11 @@ class HyperSqlDatabase extends JdbcDatabase {
 	private static final String COUNTER_TYPE =
 			"INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY(START WITH 1)";
 	private static final String STRING_TYPE = "VARCHAR";
+	private static final String SCHEMA_QUERY =
+			"SELECT TABLE_NAME FROM INFORMATION_SCHEMA.SYSTEM_TABLES"
+					+ " WHERE TABLE_TYPE='TABLE'";
 	private static final DatabaseTypes dbTypes = new DatabaseTypes(HASH_TYPE,
-			SECRET_TYPE, BINARY_TYPE, COUNTER_TYPE, STRING_TYPE);
+			SECRET_TYPE, BINARY_TYPE, COUNTER_TYPE, STRING_TYPE, SCHEMA_QUERY);
 
 	private final DatabaseConfig config;
 	private final String url;
@@ -79,11 +82,11 @@ class HyperSqlDatabase extends JdbcDatabase {
 		Connection c = null;
 		Statement s = null;
 		try {
-			super.closeAllConnections();
+			closeAllConnections();
 			c = createConnection();
 			setDirty(c, false);
 			s = c.createStatement();
-			s.executeQuery("SHUTDOWN");
+			s.executeQuery("SHUTDOWN COMPACT");
 			s.close();
 			c.close();
 		} catch (SQLException e) {
@@ -106,7 +109,7 @@ class HyperSqlDatabase extends JdbcDatabase {
 		Connection c = null;
 		Statement s = null;
 		try {
-			super.closeAllConnections();
+			closeAllConnections();
 			c = createConnection();
 			s = c.createStatement();
 			s.executeQuery("SHUTDOWN COMPACT");

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

@@ -51,7 +51,6 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
-import java.util.LinkedHashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -70,12 +69,14 @@ import static java.sql.Types.BOOLEAN;
 import static java.sql.Types.INTEGER;
 import static java.sql.Types.VARCHAR;
 import static java.util.Arrays.asList;
+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.db.DatabaseComponent.NO_CLEANUP_DEADLINE;
 import static org.briarproject.bramble.api.db.DatabaseComponent.TIMER_NOT_STARTED;
 import static org.briarproject.bramble.api.db.Metadata.REMOVE;
+import static org.briarproject.bramble.api.record.Record.RECORD_HEADER_BYTES;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
@@ -85,8 +86,6 @@ import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
 import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.DB_SETTINGS_NAMESPACE;
 import static org.briarproject.bramble.db.DatabaseConstants.DIRTY_KEY;
-import static org.briarproject.bramble.db.DatabaseConstants.LAST_COMPACTED_KEY;
-import static org.briarproject.bramble.db.DatabaseConstants.MAX_COMPACTION_INTERVAL_MS;
 import static org.briarproject.bramble.db.DatabaseConstants.SCHEMA_VERSION_KEY;
 import static org.briarproject.bramble.db.ExponentialBackoff.calculateExpiry;
 import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
@@ -102,7 +101,12 @@ import static org.briarproject.bramble.util.LogUtils.now;
 abstract class JdbcDatabase implements Database<Connection> {
 
 	// Package access for testing
-	static final int CODE_SCHEMA_VERSION = 49;
+	static final int CODE_SCHEMA_VERSION = 50;
+
+	/**
+	 * The maximum number of idle connections to keep open.
+	 */
+	private static final int MAX_CONNECTION_POOL_SIZE = 1;
 
 	// Time period offsets for incoming transport keys
 	private static final int OFFSET_PREV = -1;
@@ -252,7 +256,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " requested BOOLEAN NOT NULL,"
 					+ " expiry BIGINT NOT NULL,"
 					+ " txCount INT NOT NULL,"
-					+ " eta BIGINT NOT NULL,"
+					+ " maxLatency BIGINT," // Null if latency was reset
 					+ " PRIMARY KEY (messageId, contactId),"
 					+ " FOREIGN KEY (messageId)"
 					+ " REFERENCES messages (messageId)"
@@ -365,7 +369,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 	private final Condition connectionsChanged = connectionsLock.newCondition();
 
 	@GuardedBy("connectionsLock")
-	private final LinkedList<Connection> connections = new LinkedList<>();
+	private final LinkedList<Connection> connectionPool = new LinkedList<>();
 
 	@GuardedBy("connectionsLock")
 	private int openConnections = 0;
@@ -378,8 +382,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			throws DbException, SQLException;
 
 	// Used exclusively during open to compact the database after schema
-	// migrations or after DatabaseConstants#MAX_COMPACTION_INTERVAL_MS has
-	// elapsed
+	// migrations or if the database was not shut down cleanly
 	protected abstract void compactAndClose() throws DbException;
 
 	JdbcDatabase(DatabaseTypes databaseTypes, MessageFactory messageFactory,
@@ -402,10 +405,12 @@ abstract class JdbcDatabase implements Database<Connection> {
 		boolean compact;
 		Connection txn = startTransaction();
 		try {
+			if (LOG.isLoggable(INFO)) logSchema(txn);
 			if (reopen) {
 				Settings s = getSettings(txn, DB_SETTINGS_NAMESPACE);
 				wasDirtyOnInitialisation = isDirty(s);
-				compact = migrateSchema(txn, s, listener) || isCompactionDue(s);
+				boolean migrated = migrateSchema(txn, s, listener);
+				compact = wasDirtyOnInitialisation || migrated;
 			} else {
 				wasDirtyOnInitialisation = false;
 				createTables(txn);
@@ -435,14 +440,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 			} finally {
 				connectionsLock.unlock();
 			}
-			txn = startTransaction();
-			try {
-				storeLastCompacted(txn);
-				commitTransaction(txn);
-			} catch (DbException e) {
-				abortTransaction(txn);
-				throw e;
-			}
 		}
 	}
 
@@ -451,6 +448,24 @@ abstract class JdbcDatabase implements Database<Connection> {
 		return wasDirtyOnInitialisation;
 	}
 
+	private void logSchema(Connection txn) throws DbException {
+		Statement s = null;
+		ResultSet rs = null;
+		try {
+			s = txn.createStatement();
+			rs = s.executeQuery(dbTypes.getSchemaQuery());
+			StringBuilder sb = new StringBuilder("Tables:");
+			while (rs.next()) sb.append('\n').append(rs.getString(1));
+			LOG.info(sb.toString());
+			rs.close();
+			s.close();
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	/**
 	 * Compares the schema version stored in the database with the schema
 	 * version used by the current code and applies any suitable migrations to
@@ -502,18 +517,11 @@ abstract class JdbcDatabase implements Database<Connection> {
 				new Migration45_46(),
 				new Migration46_47(dbTypes),
 				new Migration47_48(),
-				new Migration48_49()
+				new Migration48_49(),
+				new Migration49_50()
 		);
 	}
 
-	private boolean isCompactionDue(Settings s) {
-		long lastCompacted = s.getLong(LAST_COMPACTED_KEY, 0);
-		long elapsed = clock.currentTimeMillis() - lastCompacted;
-		if (LOG.isLoggable(INFO))
-			LOG.info(elapsed + " ms since last compaction");
-		return elapsed > MAX_COMPACTION_INTERVAL_MS;
-	}
-
 	private void storeSchemaVersion(Connection txn, int version)
 			throws DbException {
 		Settings s = new Settings();
@@ -521,12 +529,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
 	}
 
-	private void storeLastCompacted(Connection txn) throws DbException {
-		Settings s = new Settings();
-		s.putLong(LAST_COMPACTED_KEY, clock.currentTimeMillis());
-		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
-	}
-
 	private boolean isDirty(Settings s) {
 		return s.getBoolean(DIRTY_KEY, false);
 	}
@@ -540,7 +542,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 	private void initialiseSettings(Connection txn) throws DbException {
 		Settings s = new Settings();
 		s.putInt(SCHEMA_VERSION_KEY, CODE_SCHEMA_VERSION);
-		s.putLong(LAST_COMPACTED_KEY, clock.currentTimeMillis());
 		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
 	}
 
@@ -595,7 +596,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 		connectionsLock.lock();
 		try {
 			if (closed) throw new DbClosedException();
-			txn = connections.poll();
+			txn = connectionPool.poll();
+			logConnectionCounts();
 		} finally {
 			connectionsLock.unlock();
 		}
@@ -606,7 +608,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 				txn.setAutoCommit(false);
 				connectionsLock.lock();
 				try {
+					// The DB may have been closed since the check above
+					if (closed) {
+						tryToClose(txn, LOG, WARNING);
+						throw new DbClosedException();
+					}
 					openConnections++;
+					logConnectionCounts();
+					connectionsChanged.signalAll();
 				} finally {
 					connectionsLock.unlock();
 				}
@@ -617,67 +626,91 @@ abstract class JdbcDatabase implements Database<Connection> {
 		return txn;
 	}
 
-	@Override
-	public void abortTransaction(Connection txn) {
-		try {
-			txn.rollback();
-			connectionsLock.lock();
-			try {
-				connections.add(txn);
-				connectionsChanged.signalAll();
-			} finally {
-				connectionsLock.unlock();
-			}
-		} catch (SQLException e) {
-			// Try to close the connection
-			logException(LOG, WARNING, e);
-			tryToClose(txn, LOG, WARNING);
-			// Whatever happens, allow the database to close
-			connectionsLock.lock();
-			try {
-				openConnections--;
-				connectionsChanged.signalAll();
-			} finally {
-				connectionsLock.unlock();
-			}
+	@GuardedBy("connectionsLock")
+	private void logConnectionCounts() {
+		if (LOG.isLoggable(FINE)) {
+			LOG.fine(openConnections + " connections open, "
+					+ connectionPool.size() + " in pool");
 		}
 	}
 
 	@Override
-	public void commitTransaction(Connection txn) throws DbException {
+	public void abortTransaction(Connection txn) {
+		// The transaction may have been aborted due to an earlier exception,
+		// so close the connection rather than returning it to the pool
 		try {
-			txn.commit();
+			txn.rollback();
 		} catch (SQLException e) {
-			throw new DbException(e);
+			logException(LOG, WARNING, e);
 		}
+		closeConnection(txn);
+	}
+
+	private void closeConnection(Connection txn) {
+		tryToClose(txn, LOG, WARNING);
 		connectionsLock.lock();
 		try {
-			connections.add(txn);
+			openConnections--;
+			logConnectionCounts();
 			connectionsChanged.signalAll();
 		} finally {
 			connectionsLock.unlock();
 		}
 	}
 
-	void closeAllConnections() throws SQLException {
+	@Override
+	public void commitTransaction(Connection txn) throws DbException {
+		// If the transaction commits successfully then return the connection
+		// to the pool, otherwise close it
+		try {
+			txn.commit();
+			returnConnectionToPool(txn);
+		} catch (SQLException e) {
+			logException(LOG, WARNING, e);
+			closeConnection(txn);
+			throw new DbException(e);
+		}
+	}
+
+	private void returnConnectionToPool(Connection txn) {
+		boolean shouldClose;
+		connectionsLock.lock();
+		try {
+			shouldClose = connectionPool.size() >= MAX_CONNECTION_POOL_SIZE;
+			if (shouldClose) openConnections--;
+			else connectionPool.add(txn);
+			logConnectionCounts();
+			connectionsChanged.signalAll();
+		} finally {
+			connectionsLock.unlock();
+		}
+		if (shouldClose) tryToClose(txn, LOG, WARNING);
+	}
+
+	void closeAllConnections() {
 		boolean interrupted = false;
 		connectionsLock.lock();
 		try {
 			closed = true;
-			for (Connection c : connections) c.close();
-			openConnections -= connections.size();
-			connections.clear();
+			for (Connection c : connectionPool) tryToClose(c, LOG, WARNING);
+			openConnections -= connectionPool.size();
+			connectionPool.clear();
 			while (openConnections > 0) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info("Waiting for " + openConnections
+							+ " connections to be closed");
+				}
 				try {
 					connectionsChanged.await();
 				} catch (InterruptedException e) {
 					LOG.warning("Interrupted while closing connections");
 					interrupted = true;
 				}
-				for (Connection c : connections) c.close();
-				openConnections -= connections.size();
-				connections.clear();
+				for (Connection c : connectionPool) tryToClose(c, LOG, WARNING);
+				openConnections -= connectionPool.size();
+				connectionPool.clear();
 			}
+			LOG.info("All connections closed");
 		} finally {
 			connectionsLock.unlock();
 		}
@@ -920,9 +953,10 @@ abstract class JdbcDatabase implements Database<Connection> {
 		try {
 			String sql = "INSERT INTO statuses (messageId, contactId, groupId,"
 					+ " timestamp, length, state, groupShared, messageShared,"
-					+ " deleted, ack, seen, requested, expiry, txCount, eta)"
+					+ " deleted, ack, seen, requested, expiry, txCount,"
+					+ " maxLatency)"
 					+ " VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, FALSE, 0, 0,"
-					+ " 0)";
+					+ " NULL)";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			ps.setInt(2, c.getInt());
@@ -1156,17 +1190,17 @@ abstract class JdbcDatabase implements Database<Connection> {
 				ps.setInt(2, DELIVERED.getValue());
 			} else {
 				long now = clock.currentTimeMillis();
-				long eta = now + maxLatency;
 				sql = "SELECT NULL FROM statuses"
 						+ " WHERE contactId = ? AND state = ?"
 						+ " AND groupShared = TRUE AND messageShared = TRUE"
 						+ " AND deleted = FALSE AND seen = FALSE"
-						+ " AND (expiry <= ? OR eta > ?)";
+						+ " AND (expiry <= ? OR maxLatency IS NULL"
+						+ " OR ? < maxLatency)";
 				ps = txn.prepareStatement(sql);
 				ps.setInt(1, c.getInt());
 				ps.setInt(2, DELIVERED.getValue());
 				ps.setLong(3, now);
-				ps.setLong(4, eta);
+				ps.setLong(4, maxLatency);
 			}
 			rs = ps.executeQuery();
 			boolean messagesToSend = rs.next();
@@ -1902,6 +1936,31 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public int getMessageLength(Connection txn, MessageId m)
+			throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT length from messages"
+					+ " WHERE messageId = ? AND state = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, m.getBytes());
+			ps.setInt(2, DELIVERED.getValue());
+			rs = ps.executeQuery();
+			if (!rs.next()) throw new DbStateException();
+			int length = rs.getInt(1);
+			if (rs.next()) throw new DbStateException();
+			rs.close();
+			ps.close();
+			return length;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public Map<MessageId, Metadata> getMessageMetadata(Connection txn,
 			GroupId g) throws DbException {
@@ -2194,7 +2253,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 	public Collection<MessageId> getMessagesToOffer(Connection txn,
 			ContactId c, int maxMessages, long maxLatency) throws DbException {
 		long now = clock.currentTimeMillis();
-		long eta = now + maxLatency;
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2203,13 +2261,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " AND groupShared = TRUE AND messageShared = TRUE"
 					+ " AND deleted = FALSE"
 					+ " AND seen = FALSE AND requested = FALSE"
-					+ " AND (expiry <= ? OR eta > ?)"
+					+ " AND (expiry <= ? OR maxLatency IS NULL"
+					+ " OR ? < maxLatency)"
 					+ " ORDER BY timestamp LIMIT ?";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, c.getInt());
 			ps.setInt(2, DELIVERED.getValue());
 			ps.setLong(3, now);
-			ps.setLong(4, eta);
+			ps.setLong(4, maxLatency);
 			ps.setInt(5, maxMessages);
 			rs = ps.executeQuery();
 			List<MessageId> ids = new ArrayList<>();
@@ -2250,10 +2309,9 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public Collection<MessageId> getMessagesToSend(Connection txn, ContactId c,
-			int maxLength, long maxLatency) throws DbException {
+	public Collection<MessageId> getMessagesToSend(Connection txn,
+			ContactId c, long capacity, long maxLatency) throws DbException {
 		long now = clock.currentTimeMillis();
-		long eta = now + maxLatency;
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2262,21 +2320,21 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " AND groupShared = TRUE AND messageShared = TRUE"
 					+ " AND deleted = FALSE"
 					+ " AND seen = FALSE"
-					+ " AND (expiry <= ? OR eta > ?)"
+					+ " AND (expiry <= ? OR maxLatency IS NULL"
+					+ " OR ? < maxLatency)"
 					+ " ORDER BY timestamp";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, c.getInt());
 			ps.setInt(2, DELIVERED.getValue());
 			ps.setLong(3, now);
-			ps.setLong(4, eta);
+			ps.setLong(4, maxLatency);
 			rs = ps.executeQuery();
 			List<MessageId> ids = new ArrayList<>();
-			int total = 0;
 			while (rs.next()) {
 				int length = rs.getInt(1);
-				if (total + length > maxLength) break;
+				if (capacity < RECORD_HEADER_BYTES + length) break;
 				ids.add(new MessageId(rs.getBytes(2)));
-				total += length;
+				capacity -= RECORD_HEADER_BYTES + length;
 			}
 			rs.close();
 			ps.close();
@@ -2289,12 +2347,12 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public Map<MessageId, Integer> getUnackedMessagesToSend(Connection txn,
+	public Collection<MessageId> getUnackedMessagesToSend(Connection txn,
 			ContactId c) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
-			String sql = "SELECT length, messageId FROM statuses"
+			String sql = "SELECT messageId FROM statuses"
 					+ " WHERE contactId = ? AND state = ?"
 					+ " AND groupShared = TRUE AND messageShared = TRUE"
 					+ " AND deleted = FALSE AND seen = FALSE"
@@ -2303,15 +2361,11 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setInt(1, c.getInt());
 			ps.setInt(2, DELIVERED.getValue());
 			rs = ps.executeQuery();
-			Map<MessageId, Integer> results = new LinkedHashMap<>();
-			while (rs.next()) {
-				int length = rs.getInt(1);
-				MessageId id = new MessageId(rs.getBytes(2));
-				results.put(id, length);
-			}
+			List<MessageId> ids = new ArrayList<>();
+			while (rs.next()) ids.add(new MessageId(rs.getBytes(1)));
 			rs.close();
 			ps.close();
-			return results;
+			return ids;
 		} catch (SQLException e) {
 			tryToClose(rs, LOG, WARNING);
 			tryToClose(ps, LOG, WARNING);
@@ -2424,6 +2478,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				MessageId m = new MessageId(rs.getBytes(1));
 				GroupId g = new GroupId(rs.getBytes(2));
 				Collection<MessageId> messageIds = ids.get(g);
+				//noinspection Java8MapApi
 				if (messageIds == null) {
 					messageIds = new ArrayList<>();
 					ids.put(g, messageIds);
@@ -2550,9 +2605,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	@Override
 	public Collection<MessageId> getRequestedMessagesToSend(Connection txn,
-			ContactId c, int maxLength, long maxLatency) throws DbException {
+			ContactId c, long capacity, long maxLatency) throws DbException {
 		long now = clock.currentTimeMillis();
-		long eta = now + maxLatency;
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2561,21 +2615,21 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " AND groupShared = TRUE AND messageShared = TRUE"
 					+ " AND deleted = FALSE"
 					+ " AND seen = FALSE AND requested = TRUE"
-					+ " AND (expiry <= ? OR eta > ?)"
+					+ " AND (expiry <= ? OR maxLatency IS NULL"
+					+ " OR ? < maxLatency)"
 					+ " ORDER BY timestamp";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, c.getInt());
 			ps.setInt(2, DELIVERED.getValue());
 			ps.setLong(3, now);
-			ps.setLong(4, eta);
+			ps.setLong(4, maxLatency);
 			rs = ps.executeQuery();
 			List<MessageId> ids = new ArrayList<>();
-			int total = 0;
 			while (rs.next()) {
 				int length = rs.getInt(1);
-				if (total + length > maxLength) break;
+				if (capacity < RECORD_HEADER_BYTES + length) break;
 				ids.add(new MessageId(rs.getBytes(2)));
-				total += length;
+				capacity -= RECORD_HEADER_BYTES + length;
 			}
 			rs.close();
 			ps.close();
@@ -2729,6 +2783,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				ContactId c = new ContactId(rs.getInt(1));
 				TransportId t = new TransportId(rs.getString(2));
 				Collection<TransportId> transportIds = ids.get(c);
+				//noinspection Java8MapApi
 				if (transportIds == null) {
 					transportIds = new ArrayList<>();
 					ids.put(c, transportIds);
@@ -3298,7 +3353,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			throws DbException {
 		PreparedStatement ps = null;
 		try {
-			String sql = "UPDATE statuses SET expiry = 0, txCount = 0, eta = 0"
+			String sql = "UPDATE statuses SET expiry = 0, txCount = 0,"
+					+ " maxLatency = NULL"
 					+ " WHERE contactId = ? AND state = ?"
 					+ " AND groupShared = TRUE AND messageShared = TRUE"
 					+ " AND deleted = FALSE AND seen = FALSE";
@@ -3643,8 +3699,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public void updateExpiryTimeAndEta(Connection txn, ContactId c, MessageId m,
-			long maxLatency) throws DbException {
+	public void updateRetransmissionData(Connection txn, ContactId c,
+			MessageId m, long maxLatency) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -3660,13 +3716,12 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs.close();
 			ps.close();
 			sql = "UPDATE statuses"
-					+ " SET expiry = ?, txCount = txCount + 1, eta = ?"
+					+ " SET expiry = ?, txCount = txCount + 1, maxLatency = ?"
 					+ " WHERE messageId = ? AND contactId = ?";
 			ps = txn.prepareStatement(sql);
 			long now = clock.currentTimeMillis();
-			long eta = now + maxLatency;
 			ps.setLong(1, calculateExpiry(now, maxLatency, txCount));
-			ps.setLong(2, eta);
+			ps.setLong(2, maxLatency);
 			ps.setBytes(3, m.getBytes());
 			ps.setInt(4, c.getInt());
 			int affected = ps.executeUpdate();

bramble-core/src/main/java/org/briarproject/bramble/db/Migration49_50.java

@@ -0,0 +1,45 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
+class Migration49_50 implements Migration<Connection> {
+
+	private static final Logger LOG = getLogger(Migration49_50.class.getName());
+
+	@Override
+	public int getStartVersion() {
+		return 49;
+	}
+
+	@Override
+	public int getEndVersion() {
+		return 50;
+	}
+
+	@Override
+	public void migrate(Connection txn) throws DbException {
+		Statement s = null;
+		try {
+			s = txn.createStatement();
+			s.execute("ALTER TABLE statuses"
+					+ " ALTER COLUMN eta"
+					+ " RENAME TO maxLatency");
+			s.execute("ALTER TABLE statuses"
+					+ " ALTER COLUMN maxLatency"
+					+ " SET NULL");
+			s.execute("UPDATE statuses SET maxLatency = NULL");
+		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+}

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

@@ -1,10 +1,10 @@
 package org.briarproject.bramble.io;
 
+import org.briarproject.bramble.api.Cancellable;
 import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.TaskScheduler;
-import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
 import org.briarproject.bramble.api.system.Wakeful;
 
 import java.io.IOException;

bramble-core/src/main/java/org/briarproject/bramble/lifecycle/LifecycleManagerImpl.java

@@ -190,6 +190,10 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 			return;
 		}
 		try {
+			if (state == STOPPING) {
+				LOG.info("Already stopped");
+				return;
+			}
 			LOG.info("Stopping services");
 			state = STOPPING;
 			eventBus.broadcast(new LifecycleEvent(STOPPING));

bramble-core/src/main/java/org/briarproject/bramble/mailbox/ApiCall.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
+
+/**
+ * An interface for calling an API endpoint with the option to retry the call.
+ */
+interface ApiCall {
+
+	/**
+	 * This method makes a synchronous call to an API endpoint and returns
+	 * true if the call should be retried, in which case the method may be
+	 * called again on the same {@link ApiCall} instance after a delay.
+	 *
+	 * @return True if the API call needs to be retried, or false if the API
+	 * call succeeded or {@link TolerableFailureException failed tolerably}.
+	 */
+	@IoExecutor
+	boolean callApi();
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/ConnectivityChecker.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * An interface for checking whether a mailbox is reachable.
+ */
+@ThreadSafe
+@NotNullByDefault
+interface ConnectivityChecker {
+
+	/**
+	 * Destroys the checker. Any current connectivity check is cancelled.
+	 */
+	void destroy();
+
+	/**
+	 * Starts a connectivity check if needed and calls the given observer when
+	 * the check succeeds. If a check is already running then the observer is
+	 * called when the check succeeds. If a connectivity check has recently
+	 * succeeded then the observer is called immediately.
+	 */
+	void checkConnectivity(MailboxProperties properties,
+			ConnectivityObserver o);
+
+	interface ConnectivityObserver {
+		void onConnectivityCheckSucceeded();
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/ConnectivityCheckerImpl.java

@@ -0,0 +1,111 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.Cancellable;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Clock;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+@ThreadSafe
+@NotNullByDefault
+abstract class ConnectivityCheckerImpl implements ConnectivityChecker {
+
+	/**
+	 * If no more than this much time has elapsed since the last connectivity
+	 * check succeeded, consider the result to be fresh and don't check again.
+	 * <p>
+	 * Package access for testing.
+	 */
+	static final long CONNECTIVITY_CHECK_FRESHNESS_MS = 10_000;
+
+	private final Object lock = new Object();
+
+	protected final Clock clock;
+	private final MailboxApiCaller mailboxApiCaller;
+
+	@GuardedBy("lock")
+	private boolean destroyed = false;
+
+	@GuardedBy("lock")
+	@Nullable
+	private Cancellable connectivityCheck = null;
+
+	@GuardedBy("lock")
+	private long lastConnectivityCheckSucceeded = 0;
+
+	@GuardedBy("lock")
+	private final List<ConnectivityObserver> connectivityObservers =
+			new ArrayList<>();
+
+	/**
+	 * Creates an {@link ApiCall} for checking whether the mailbox is
+	 * reachable. The {@link ApiCall} should call
+	 * {@link #onConnectivityCheckSucceeded(long)} if the check succeeds.
+	 */
+	abstract ApiCall createConnectivityCheckTask(MailboxProperties properties);
+
+	ConnectivityCheckerImpl(Clock clock, MailboxApiCaller mailboxApiCaller) {
+		this.clock = clock;
+		this.mailboxApiCaller = mailboxApiCaller;
+	}
+
+	@Override
+	public void destroy() {
+		synchronized (lock) {
+			destroyed = true;
+			connectivityObservers.clear();
+			if (connectivityCheck != null) {
+				connectivityCheck.cancel();
+				connectivityCheck = null;
+			}
+		}
+	}
+
+	@Override
+	public void checkConnectivity(MailboxProperties properties,
+			ConnectivityObserver o) {
+		boolean callNow = false;
+		synchronized (lock) {
+			if (destroyed) return;
+			if (connectivityCheck == null) {
+				// No connectivity check is running
+				long now = clock.currentTimeMillis();
+				if (now - lastConnectivityCheckSucceeded
+						> CONNECTIVITY_CHECK_FRESHNESS_MS) {
+					// The last connectivity check is stale, start a new one
+					connectivityObservers.add(o);
+					ApiCall task =
+							createConnectivityCheckTask(properties);
+					connectivityCheck = mailboxApiCaller.retryWithBackoff(task);
+				} else {
+					// The last connectivity check is fresh
+					callNow = true;
+				}
+			} else {
+				// A connectivity check is running, wait for it to succeed
+				connectivityObservers.add(o);
+			}
+		}
+		if (callNow) o.onConnectivityCheckSucceeded();
+	}
+
+	protected void onConnectivityCheckSucceeded(long now) {
+		List<ConnectivityObserver> observers;
+		synchronized (lock) {
+			if (destroyed) return;
+			connectivityCheck = null;
+			lastConnectivityCheckSucceeded = now;
+			observers = new ArrayList<>(connectivityObservers);
+			connectivityObservers.clear();
+		}
+		for (ConnectivityObserver o : observers) {
+			o.onConnectivityCheckSucceeded();
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/ContactMailboxConnectivityChecker.java

@@ -0,0 +1,39 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
+
+import java.io.IOException;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+@ThreadSafe
+@NotNullByDefault
+class ContactMailboxConnectivityChecker extends ConnectivityCheckerImpl {
+
+	private final MailboxApi mailboxApi;
+
+	ContactMailboxConnectivityChecker(Clock clock,
+			MailboxApiCaller mailboxApiCaller, MailboxApi mailboxApi) {
+		super(clock, mailboxApiCaller);
+		this.mailboxApi = mailboxApi;
+	}
+
+	@Override
+	ApiCall createConnectivityCheckTask(MailboxProperties properties) {
+		if (properties.isOwner()) throw new IllegalArgumentException();
+		return new SimpleApiCall() {
+			@Override
+			void tryToCallApi() throws IOException, ApiException {
+				if (!mailboxApi.checkStatus(properties)) {
+					throw new ApiException();
+				}
+				// Call the observers and cache the result
+				onConnectivityCheckSucceeded(clock.currentTimeMillis());
+			}
+		};
+	}
+
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApi.java

@@ -7,6 +7,8 @@ import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
 import org.briarproject.bramble.api.mailbox.MailboxFileId;
 import org.briarproject.bramble.api.mailbox.MailboxFolderId;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.File;
 import java.io.IOException;
@@ -16,8 +18,12 @@ import java.util.List;
 import javax.annotation.Nonnull;
 import javax.annotation.concurrent.Immutable;
 
+@NotNullByDefault
 interface MailboxApi {
 
+	List<MailboxVersion> getServerSupports(MailboxProperties properties)
+			throws IOException, ApiException;
+
 	/**
 	 * Sets up the mailbox with the setup token.
 	 *
@@ -25,7 +31,7 @@ interface MailboxApi {
 	 * @return the owner token
 	 * @throws ApiException for 401 response.
 	 */
-	MailboxAuthToken setup(MailboxProperties properties)
+	MailboxProperties setup(MailboxProperties properties)
 			throws IOException, ApiException;
 
 	/**

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiCaller.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.Cancellable;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static java.util.concurrent.TimeUnit.MINUTES;
+
+@NotNullByDefault
+interface MailboxApiCaller {
+
+	/**
+	 * The minimum interval between retries in milliseconds.
+	 */
+	long MIN_RETRY_INTERVAL_MS = MINUTES.toMillis(1);
+
+	/**
+	 * The maximum interval between retries in milliseconds.
+	 */
+	long MAX_RETRY_INTERVAL_MS = DAYS.toMillis(1);
+
+	/**
+	 * Asynchronously calls the given API call on the {@link IoExecutor},
+	 * automatically retrying at increasing intervals until the API call
+	 * returns false or retries are cancelled.
+	 *
+	 * @return A {@link Cancellable} that can be used to cancel any future
+	 * retries.
+	 */
+	Cancellable retryWithBackoff(ApiCall apiCall);
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiCallerImpl.java

@@ -0,0 +1,98 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.Cancellable;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.TaskScheduler;
+
+import java.util.concurrent.Executor;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static java.lang.Math.min;
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+
+@Immutable
+@NotNullByDefault
+class MailboxApiCallerImpl implements MailboxApiCaller {
+
+	private final TaskScheduler taskScheduler;
+	private final Executor ioExecutor;
+
+	@Inject
+	MailboxApiCallerImpl(TaskScheduler taskScheduler,
+			@IoExecutor Executor ioExecutor) {
+		this.taskScheduler = taskScheduler;
+		this.ioExecutor = ioExecutor;
+	}
+
+	@Override
+	public Cancellable retryWithBackoff(ApiCall apiCall) {
+		Task task = new Task(apiCall);
+		task.start();
+		return task;
+	}
+
+	private class Task implements Cancellable {
+
+		private final ApiCall apiCall;
+		private final Object lock = new Object();
+
+		@GuardedBy("lock")
+		@Nullable
+		private Cancellable scheduledTask = null;
+
+		@GuardedBy("lock")
+		private boolean cancelled = false;
+
+		@GuardedBy("lock")
+		private long retryIntervalMs = MIN_RETRY_INTERVAL_MS;
+
+		private Task(ApiCall apiCall) {
+			this.apiCall = apiCall;
+		}
+
+		private void start() {
+			synchronized (lock) {
+				if (cancelled) throw new AssertionError();
+				ioExecutor.execute(this::callApi);
+			}
+		}
+
+		@IoExecutor
+		private void callApi() {
+			synchronized (lock) {
+				if (cancelled) return;
+			}
+			// The call returns true if we should retry
+			if (apiCall.callApi()) {
+				synchronized (lock) {
+					if (cancelled) return;
+					scheduledTask = taskScheduler.schedule(this::callApi,
+							ioExecutor, retryIntervalMs, MILLISECONDS);
+					// Increase the retry interval each time we retry
+					retryIntervalMs =
+							min(MAX_RETRY_INTERVAL_MS, retryIntervalMs * 2);
+				}
+			} else {
+				synchronized (lock) {
+					scheduledTask = null;
+				}
+			}
+		}
+
+		@Override
+		public void cancel() {
+			Cancellable scheduledTask;
+			synchronized (lock) {
+				cancelled = true;
+				scheduledTask = this.scheduledTask;
+				this.scheduledTask = null;
+			}
+			if (scheduledTask != null) scheduledTask.cancel();
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiImpl.java

@@ -14,6 +14,7 @@ import org.briarproject.bramble.api.mailbox.MailboxFileId;
 import org.briarproject.bramble.api.mailbox.MailboxFolderId;
 import org.briarproject.bramble.api.mailbox.MailboxId;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.File;
@@ -56,7 +57,24 @@ class MailboxApiImpl implements MailboxApi {
 	}
 
 	@Override
-	public MailboxAuthToken setup(MailboxProperties properties)
+	public List<MailboxVersion> getServerSupports(MailboxProperties properties)
+			throws IOException, ApiException {
+		if (!properties.isOwner()) throw new IllegalArgumentException();
+		Response response = sendGetRequest(properties, "/versions");
+		if (response.code() != 200) throw new ApiException();
+
+		ResponseBody body = response.body();
+		if (body == null) throw new ApiException();
+		try {
+			JsonNode node = mapper.readTree(body.string());
+			return parseServerSupports(node);
+		} catch (JacksonException e) {
+			throw new ApiException();
+		}
+	}
+
+	@Override
+	public MailboxProperties setup(MailboxProperties properties)
 			throws IOException, ApiException {
 		if (!properties.isOwner()) throw new IllegalArgumentException();
 		Request request = getRequestBuilder(properties.getAuthToken())
@@ -75,17 +93,40 @@ class MailboxApiImpl implements MailboxApi {
 			if (tokenNode == null) {
 				throw new ApiException();
 			}
-			String ownerToken = tokenNode.textValue();
-			return MailboxAuthToken.fromString(ownerToken);
+			return new MailboxProperties(properties.getBaseUrl(),
+					MailboxAuthToken.fromString(tokenNode.textValue()),
+					parseServerSupports(node));
 		} catch (JacksonException | InvalidMailboxIdException e) {
 			throw new ApiException();
 		}
 	}
 
+	private List<MailboxVersion> parseServerSupports(JsonNode node)
+			throws ApiException {
+		List<MailboxVersion> serverSupports = new ArrayList<>();
+		ArrayNode serverSupportsNode = getArray(node, "serverSupports");
+		for (JsonNode versionNode : serverSupportsNode) {
+			if (!versionNode.isObject()) throw new ApiException();
+			ObjectNode objectNode = (ObjectNode) versionNode;
+			JsonNode majorNode = objectNode.get("major");
+			JsonNode minorNode = objectNode.get("minor");
+			if (majorNode == null || !majorNode.isNumber()) {
+				throw new ApiException();
+			}
+			if (minorNode == null || !minorNode.isNumber()) {
+				throw new ApiException();
+			}
+			int major = majorNode.asInt();
+			int minor = minorNode.asInt();
+			if (major < 0 || minor < 0) throw new ApiException();
+			serverSupports.add(new MailboxVersion(major, minor));
+		}
+		return serverSupports;
+	}
+
 	@Override
 	public boolean checkStatus(MailboxProperties properties)
 			throws IOException, ApiException {
-		if (!properties.isOwner()) throw new IllegalArgumentException();
 		Response response = sendGetRequest(properties, "/status");
 		if (response.code() == 401) throw new ApiException();
 		return response.isSuccessful();

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxFileManager.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.io.File;
+import java.io.IOException;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+@ThreadSafe
+@NotNullByDefault
+interface MailboxFileManager {
+
+	/**
+	 * Creates an empty file for storing a download.
+	 */
+	File createTempFileForDownload() throws IOException;
+
+	/**
+	 * Handles a file that has been downloaded. The file should be created
+	 * with {@link #createTempFileForDownload()}.
+	 */
+	void handleDownloadedFile(File f);
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxFileManagerImpl.java

@@ -0,0 +1,174 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventListener;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.mailbox.MailboxDirectory;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.api.plugin.file.FileConstants.PROP_PATH;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@ThreadSafe
+@NotNullByDefault
+class MailboxFileManagerImpl implements MailboxFileManager, EventListener {
+
+	private static final Logger LOG =
+			getLogger(MailboxFileManagerImpl.class.getName());
+
+	// Package access for testing
+	static final String DOWNLOAD_DIR_NAME = "downloads";
+
+	private final Executor ioExecutor;
+	private final PluginManager pluginManager;
+	private final ConnectionManager connectionManager;
+	private final LifecycleManager lifecycleManager;
+	private final File mailboxDir;
+	private final EventBus eventBus;
+	private final CountDownLatch orphanLatch = new CountDownLatch(1);
+
+	@Inject
+	MailboxFileManagerImpl(@IoExecutor Executor ioExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			LifecycleManager lifecycleManager,
+			@MailboxDirectory File mailboxDir,
+			EventBus eventBus) {
+		this.ioExecutor = ioExecutor;
+		this.pluginManager = pluginManager;
+		this.connectionManager = connectionManager;
+		this.lifecycleManager = lifecycleManager;
+		this.mailboxDir = mailboxDir;
+		this.eventBus = eventBus;
+	}
+
+	@Override
+	public File createTempFileForDownload() throws IOException {
+		// Wait for orphaned files to be handled before creating new files
+		try {
+			orphanLatch.await();
+		} catch (InterruptedException e) {
+			throw new IOException(e);
+		}
+		File downloadDir = createDirectoryIfNeeded(DOWNLOAD_DIR_NAME);
+		return File.createTempFile("mailbox", ".tmp", downloadDir);
+	}
+
+	private File createDirectoryIfNeeded(String name) throws IOException {
+		File dir = new File(mailboxDir, name);
+		//noinspection ResultOfMethodCallIgnored
+		dir.mkdirs();
+		if (!dir.isDirectory()) {
+			throw new IOException("Failed to create directory '" + name + "'");
+		}
+		return dir;
+	}
+
+	@Override
+	public void handleDownloadedFile(File f) {
+		// We shouldn't reach this point until the plugin has been started
+		SimplexPlugin plugin =
+				(SimplexPlugin) requireNonNull(pluginManager.getPlugin(ID));
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_PATH, f.getAbsolutePath());
+		TransportConnectionReader reader = plugin.createReader(p);
+		if (reader == null) {
+			LOG.warning("Failed to create reader for downloaded file");
+			return;
+		}
+		TransportConnectionReader decorated = new MailboxFileReader(reader, f);
+		LOG.info("Reading downloaded file");
+		connectionManager.manageIncomingConnection(ID, decorated,
+				exception -> isHandlingComplete(exception, true));
+	}
+
+	private boolean isHandlingComplete(boolean exception, boolean recognised) {
+		// If we've successfully read the file then we're done
+		if (!exception && recognised) return true;
+		// If the app is shutting down we may get spurious IO exceptions
+		// due to executors being shut down. Leave the file in the download
+		// directory and we'll try to read it again at the next startup
+		return !lifecycleManager.getLifecycleState().isAfter(RUNNING);
+	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
+			if (t.getTransportId().equals(ID)) {
+				ioExecutor.execute(this::handleOrphanedFiles);
+				eventBus.removeListener(this);
+			}
+		}
+	}
+
+	/**
+	 * This method is called at startup, as soon as the plugin is started, to
+	 * handle any files that were left in the download directory at the last
+	 * shutdown.
+	 */
+	@IoExecutor
+	private void handleOrphanedFiles() {
+		try {
+			File downloadDir = createDirectoryIfNeeded(DOWNLOAD_DIR_NAME);
+			File[] orphans = downloadDir.listFiles();
+			// Now that we've got the list of orphans, new files can be created
+			orphanLatch.countDown();
+			if (orphans != null) for (File f : orphans) handleDownloadedFile(f);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+
+	private class MailboxFileReader implements TransportConnectionReader {
+
+		private final TransportConnectionReader delegate;
+		private final File file;
+
+		private MailboxFileReader(TransportConnectionReader delegate,
+				File file) {
+			this.delegate = delegate;
+			this.file = file;
+		}
+
+		@Override
+		public InputStream getInputStream() throws IOException {
+			return delegate.getInputStream();
+		}
+
+		@Override
+		public void dispose(boolean exception, boolean recognised)
+				throws IOException {
+			delegate.dispose(exception, recognised);
+			if (isHandlingComplete(exception, recognised)) {
+				LOG.info("Deleting downloaded file");
+				if (!file.delete()) {
+					LOG.warning("Failed to delete downloaded file");
+				}
+			}
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxManagerImpl.java

@@ -2,27 +2,42 @@ package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.mailbox.MailboxManager;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
 import org.briarproject.bramble.api.mailbox.MailboxStatus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Clock;
 
+import java.io.IOException;
 import java.util.concurrent.Executor;
+import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
 @Immutable
 @NotNullByDefault
 class MailboxManagerImpl implements MailboxManager {
 
+	private static final String TAG = MailboxManagerImpl.class.getName();
+	private final static Logger LOG = getLogger(TAG);
+
 	private final Executor ioExecutor;
+	private final MailboxApi api;
+	private final TransactionManager db;
 	private final MailboxSettingsManager mailboxSettingsManager;
 	private final MailboxPairingTaskFactory pairingTaskFactory;
+	private final Clock clock;
 	private final Object lock = new Object();
 
 	@Nullable
@@ -32,11 +47,17 @@ class MailboxManagerImpl implements MailboxManager {
 	@Inject
 	MailboxManagerImpl(
 			@IoExecutor Executor ioExecutor,
+			MailboxApi api,
+			TransactionManager db,
 			MailboxSettingsManager mailboxSettingsManager,
-			MailboxPairingTaskFactory pairingTaskFactory) {
+			MailboxPairingTaskFactory pairingTaskFactory,
+			Clock clock) {
 		this.ioExecutor = ioExecutor;
+		this.api = api;
+		this.db = db;
 		this.mailboxSettingsManager = mailboxSettingsManager;
 		this.pairingTaskFactory = pairingTaskFactory;
+		this.clock = clock;
 	}
 
 	@Override
@@ -75,4 +96,61 @@ class MailboxManagerImpl implements MailboxManager {
 		return created;
 	}
 
+	@Override
+	public boolean checkConnection() {
+		boolean success;
+		try {
+			MailboxProperties props = db.transactionWithNullableResult(true,
+					mailboxSettingsManager::getOwnMailboxProperties);
+			if (props == null) throw new DbException();
+			success = api.checkStatus(props);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			// we don't treat this is a failure to record
+			return false;
+		} catch (IOException | MailboxApi.ApiException e) {
+			// we record this as a failure
+			success = false;
+			logException(LOG, WARNING, e);
+		}
+		try {
+			recordCheckResult(success);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+		}
+		return success;
+	}
+
+	private void recordCheckResult(boolean success) throws DbException {
+		long now = clock.currentTimeMillis();
+		db.transaction(false, txn -> {
+			if (success) {
+				mailboxSettingsManager.recordSuccessfulConnection(txn, now);
+			} else {
+				mailboxSettingsManager.recordFailedConnectionAttempt(txn, now);
+			}
+		});
+	}
+
+	@Override
+	public boolean unPair() throws DbException {
+		MailboxProperties properties = db.transactionWithNullableResult(true,
+				mailboxSettingsManager::getOwnMailboxProperties);
+		if (properties == null) {
+			// no more mailbox, that's strange but possible if called in quick
+			// succession, so let's return true this time
+			return true;
+		}
+		boolean wasWiped;
+		try {
+			api.wipeMailbox(properties);
+			wasWiped = true;
+		} catch (IOException | MailboxApi.ApiException e) {
+			logException(LOG, WARNING, e);
+			wasWiped = false;
+		}
+		db.transaction(false,
+				mailboxSettingsManager::removeOwnMailboxProperties);
+		return wasWiped;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxModule.java

@@ -1,16 +1,44 @@
 package org.briarproject.bramble.mailbox;
 
+import org.briarproject.bramble.api.FeatureFlags;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.mailbox.MailboxManager;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 
+import java.util.List;
+
+import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
 import dagger.Provides;
 
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.CLIENT_SUPPORTS;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.CLIENT_ID;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.MAJOR_VERSION;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.MINOR_VERSION;
+
 @Module
 public class MailboxModule {
 
+	public static class EagerSingletons {
+		@Inject
+		MailboxUpdateValidator mailboxUpdateValidator;
+		@Inject
+		MailboxUpdateManager mailboxUpdateManager;
+		@Inject
+		MailboxFileManager mailboxFileManager;
+	}
+
 	@Provides
 	@Singleton
 	MailboxManager providesMailboxManager(MailboxManagerImpl mailboxManager) {
@@ -33,4 +61,57 @@ public class MailboxModule {
 	MailboxApi providesMailboxApi(MailboxApiImpl mailboxApi) {
 		return mailboxApi;
 	}
+
+	@Provides
+	@Singleton
+	MailboxUpdateValidator provideMailboxUpdateValidator(
+			ValidationManager validationManager,
+			ClientHelper clientHelper,
+			MetadataEncoder metadataEncoder,
+			Clock clock,
+			FeatureFlags featureFlags) {
+		MailboxUpdateValidator validator = new MailboxUpdateValidator(
+				clientHelper, metadataEncoder, clock);
+		if (featureFlags.shouldEnableMailbox()) {
+			validationManager.registerMessageValidator(CLIENT_ID,
+					MAJOR_VERSION, validator);
+		}
+		return validator;
+	}
+
+	@Provides
+	List<MailboxVersion> provideClientSupports() {
+		return CLIENT_SUPPORTS;
+	}
+
+	@Provides
+	@Singleton
+	MailboxUpdateManager provideMailboxUpdateManager(
+			FeatureFlags featureFlags,
+			LifecycleManager lifecycleManager,
+			ValidationManager validationManager, ContactManager contactManager,
+			ClientVersioningManager clientVersioningManager,
+			MailboxSettingsManager mailboxSettingsManager,
+			MailboxUpdateManagerImpl mailboxUpdateManager) {
+		if (featureFlags.shouldEnableMailbox()) {
+			lifecycleManager.registerOpenDatabaseHook(mailboxUpdateManager);
+			validationManager.registerIncomingMessageHook(CLIENT_ID,
+					MAJOR_VERSION, mailboxUpdateManager);
+			contactManager.registerContactHook(mailboxUpdateManager);
+			clientVersioningManager.registerClient(CLIENT_ID, MAJOR_VERSION,
+					MINOR_VERSION, mailboxUpdateManager);
+			mailboxSettingsManager.registerMailboxHook(mailboxUpdateManager);
+		}
+		return mailboxUpdateManager;
+	}
+
+	@Provides
+	@Singleton
+	MailboxFileManager provideMailboxFileManager(FeatureFlags featureFlags,
+			EventBus eventBus, MailboxFileManagerImpl mailboxFileManager) {
+		if (featureFlags.shouldEnableMailbox()) {
+			eventBus.addListener(mailboxFileManager);
+		}
+		return mailboxFileManager;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxPairingTaskFactoryImpl.java

@@ -1,10 +1,11 @@
 package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.crypto.CryptoComponent;
-import org.briarproject.bramble.api.db.TransactionManager;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Clock;
 
@@ -18,31 +19,35 @@ import javax.inject.Inject;
 class MailboxPairingTaskFactoryImpl implements MailboxPairingTaskFactory {
 
 	private final Executor eventExecutor;
-	private final TransactionManager db;
+	private final DatabaseComponent db;
 	private final CryptoComponent crypto;
 	private final Clock clock;
 	private final MailboxApi api;
 	private final MailboxSettingsManager mailboxSettingsManager;
+	private final MailboxUpdateManager mailboxUpdateManager;
 
 	@Inject
 	MailboxPairingTaskFactoryImpl(
 			@EventExecutor Executor eventExecutor,
-			TransactionManager db,
+			DatabaseComponent db,
 			CryptoComponent crypto,
 			Clock clock,
 			MailboxApi api,
-			MailboxSettingsManager mailboxSettingsManager) {
+			MailboxSettingsManager mailboxSettingsManager,
+			MailboxUpdateManager mailboxUpdateManager) {
 		this.eventExecutor = eventExecutor;
 		this.db = db;
 		this.crypto = crypto;
 		this.clock = clock;
 		this.api = api;
 		this.mailboxSettingsManager = mailboxSettingsManager;
+		this.mailboxUpdateManager = mailboxUpdateManager;
 	}
 
 	@Override
 	public MailboxPairingTask createPairingTask(String qrCodePayload) {
 		return new MailboxPairingTaskImpl(qrCodePayload, eventExecutor, db,
-				crypto, clock, api, mailboxSettingsManager);
+				crypto, clock, api, mailboxSettingsManager,
+				mailboxUpdateManager);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxPairingTaskImpl.java

@@ -2,15 +2,18 @@ package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.Consumer;
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
 import org.briarproject.bramble.api.mailbox.MailboxPairingState;
 import org.briarproject.bramble.api.mailbox.MailboxPairingTask;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
@@ -43,11 +46,12 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 
 	private final String payload;
 	private final Executor eventExecutor;
-	private final TransactionManager db;
+	private final DatabaseComponent db;
 	private final CryptoComponent crypto;
 	private final Clock clock;
 	private final MailboxApi api;
 	private final MailboxSettingsManager mailboxSettingsManager;
+	private final MailboxUpdateManager mailboxUpdateManager;
 
 	private final Object lock = new Object();
 	@GuardedBy("lock")
@@ -59,11 +63,12 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 	MailboxPairingTaskImpl(
 			String payload,
 			@EventExecutor Executor eventExecutor,
-			TransactionManager db,
+			DatabaseComponent db,
 			CryptoComponent crypto,
 			Clock clock,
 			MailboxApi api,
-			MailboxSettingsManager mailboxSettingsManager) {
+			MailboxSettingsManager mailboxSettingsManager,
+			MailboxUpdateManager mailboxUpdateManager) {
 		this.payload = payload;
 		this.eventExecutor = eventExecutor;
 		this.db = db;
@@ -71,7 +76,8 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 		this.clock = clock;
 		this.api = api;
 		this.mailboxSettingsManager = mailboxSettingsManager;
-		state = new MailboxPairingState.QrCodeReceived(payload);
+		this.mailboxUpdateManager = mailboxUpdateManager;
+		state = new MailboxPairingState.QrCodeReceived();
 	}
 
 	@Override
@@ -100,23 +106,31 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 		} catch (MailboxAlreadyPairedException e) {
 			onMailboxError(e, new MailboxPairingState.MailboxAlreadyPaired());
 		} catch (IOException e) {
-			onMailboxError(e, new MailboxPairingState.ConnectionError(payload));
+			onMailboxError(e, new MailboxPairingState.ConnectionError());
 		} catch (ApiException | DbException e) {
-			onMailboxError(e, new MailboxPairingState.UnexpectedError(payload));
+			onMailboxError(e, new MailboxPairingState.UnexpectedError());
 		}
 	}
 
 	private void pairMailbox() throws IOException, ApiException, DbException {
 		MailboxProperties mailboxProperties = decodeQrCodePayload(payload);
-		setState(new MailboxPairingState.Pairing(payload));
-		MailboxAuthToken ownerToken = api.setup(mailboxProperties);
-		MailboxProperties ownerProperties = new MailboxProperties(
-				mailboxProperties.getBaseUrl(), ownerToken, true);
+		setState(new MailboxPairingState.Pairing());
+		MailboxProperties ownerProperties = api.setup(mailboxProperties);
 		long time = clock.currentTimeMillis();
 		db.transaction(false, txn -> {
 			mailboxSettingsManager
 					.setOwnMailboxProperties(txn, ownerProperties);
 			mailboxSettingsManager.recordSuccessfulConnection(txn, time);
+			// A (possibly new) mailbox is paired. Reset message retransmission
+			// timers for contacts who doesn't have their own mailbox. This way,
+			// data stranded on our old mailbox will be re-uploaded to our new.
+			for (Contact c : db.getContacts(txn)) {
+				MailboxUpdate update = mailboxUpdateManager.getRemoteUpdate(
+						txn, c.getId());
+				if (update == null || !update.hasMailbox()) {
+					db.resetUnackedMessagesToSend(txn, c.getId());
+				}
+			}
 		});
 		setState(new MailboxPairingState.Paired());
 	}
@@ -162,11 +176,11 @@ class MailboxPairingTaskImpl implements MailboxPairingTask {
 		}
 		LOG.info("QR code is valid");
 		byte[] onionPubKey = Arrays.copyOfRange(bytes, 1, 33);
-		String onionAddress = crypto.encodeOnionAddress(onionPubKey);
-		String baseUrl = "http://" + onionAddress + ".onion";
+		String onion = crypto.encodeOnion(onionPubKey);
+		String baseUrl = "http://" + onion + ".onion"; // TODO
 		byte[] tokenBytes = Arrays.copyOfRange(bytes, 33, 65);
 		MailboxAuthToken setupToken = new MailboxAuthToken(tokenBytes);
-		return new MailboxProperties(baseUrl, setupToken, true);
+		return new MailboxProperties(baseUrl, setupToken, new ArrayList<>());
 	}
 
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxSettingsManagerImpl.java

@@ -8,14 +8,22 @@ import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
 import org.briarproject.bramble.api.mailbox.MailboxStatus;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
+import org.briarproject.bramble.api.mailbox.event.MailboxProblemEvent;
+import org.briarproject.bramble.api.mailbox.event.OwnMailboxConnectionStatusEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.settings.Settings;
 import org.briarproject.bramble.api.settings.SettingsManager;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
+import static java.util.Collections.emptyList;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 @Immutable
@@ -24,20 +32,28 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 
 	// Package access for testing
 	static final String SETTINGS_NAMESPACE = "mailbox";
+	// TODO: This currently stores the base URL, not the 56-char onion address
 	static final String SETTINGS_KEY_ONION = "onion";
 	static final String SETTINGS_KEY_TOKEN = "token";
+	static final String SETTINGS_KEY_SERVER_SUPPORTS = "serverSupports";
 	static final String SETTINGS_KEY_LAST_ATTEMPT = "lastAttempt";
 	static final String SETTINGS_KEY_LAST_SUCCESS = "lastSuccess";
 	static final String SETTINGS_KEY_ATTEMPTS = "attempts";
 	static final String SETTINGS_UPLOADS_NAMESPACE = "mailbox-uploads";
 
 	private final SettingsManager settingsManager;
+	private final List<MailboxHook> hooks = new CopyOnWriteArrayList<>();
 
 	@Inject
 	MailboxSettingsManagerImpl(SettingsManager settingsManager) {
 		this.settingsManager = settingsManager;
 	}
 
+	@Override
+	public void registerMailboxHook(MailboxHook hook) {
+		hooks.add(hook);
+	}
+
 	@Override
 	public MailboxProperties getOwnMailboxProperties(Transaction txn)
 			throws DbException {
@@ -45,9 +61,10 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 		String onion = s.get(SETTINGS_KEY_ONION);
 		String token = s.get(SETTINGS_KEY_TOKEN);
 		if (isNullOrEmpty(onion) || isNullOrEmpty(token)) return null;
+		List<MailboxVersion> serverSupports = parseServerSupports(s);
 		try {
 			MailboxAuthToken tokenId = MailboxAuthToken.fromString(token);
-			return new MailboxProperties(onion, tokenId, true);
+			return new MailboxProperties(onion, tokenId, serverSupports);
 		} catch (InvalidMailboxIdException e) {
 			throw new DbException(e);
 		}
@@ -59,7 +76,29 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 		Settings s = new Settings();
 		s.put(SETTINGS_KEY_ONION, p.getBaseUrl());
 		s.put(SETTINGS_KEY_TOKEN, p.getAuthToken().toString());
+		List<MailboxVersion> serverSupports = p.getServerSupports();
+		int[] ints = new int[serverSupports.size() * 2];
+		int i = 0;
+		for (MailboxVersion v : serverSupports) {
+			ints[i++] = v.getMajor();
+			ints[i++] = v.getMinor();
+		}
+		s.putIntArray(SETTINGS_KEY_SERVER_SUPPORTS, ints);
 		settingsManager.mergeSettings(txn, s, SETTINGS_NAMESPACE);
+		for (MailboxHook hook : hooks) {
+			hook.mailboxPaired(txn, p.getOnion(), p.getServerSupports());
+		}
+	}
+
+	@Override
+	public void removeOwnMailboxProperties(Transaction txn) throws DbException {
+		Settings s = new Settings();
+		s.put(SETTINGS_KEY_ONION, "");
+		s.put(SETTINGS_KEY_TOKEN, "");
+		settingsManager.mergeSettings(txn, s, SETTINGS_NAMESPACE);
+		for (MailboxHook hook : hooks) {
+			hook.mailboxUnpaired(txn);
+		}
 	}
 
 	@Override
@@ -69,17 +108,29 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 		long lastAttempt = s.getLong(SETTINGS_KEY_LAST_ATTEMPT, -1);
 		long lastSuccess = s.getLong(SETTINGS_KEY_LAST_SUCCESS, -1);
 		int attempts = s.getInt(SETTINGS_KEY_ATTEMPTS, 0);
-		return new MailboxStatus(lastAttempt, lastSuccess, attempts);
+		List<MailboxVersion> serverSupports;
+		try {
+			serverSupports = parseServerSupports(s);
+		} catch (DbException e) {
+			serverSupports = emptyList();
+		}
+		return new MailboxStatus(lastAttempt, lastSuccess, attempts,
+				serverSupports);
 	}
 
 	@Override
 	public void recordSuccessfulConnection(Transaction txn, long now)
 			throws DbException {
+		Settings oldSettings =
+				settingsManager.getSettings(txn, SETTINGS_NAMESPACE);
 		Settings s = new Settings();
 		s.putLong(SETTINGS_KEY_LAST_ATTEMPT, now);
 		s.putLong(SETTINGS_KEY_LAST_SUCCESS, now);
 		s.putInt(SETTINGS_KEY_ATTEMPTS, 0);
 		settingsManager.mergeSettings(txn, s, SETTINGS_NAMESPACE);
+		List<MailboxVersion> serverSupports = parseServerSupports(oldSettings);
+		MailboxStatus status = new MailboxStatus(now, now, 0, serverSupports);
+		txn.attach(new OwnMailboxConnectionStatusEvent(status));
 	}
 
 	@Override
@@ -87,11 +138,17 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 			throws DbException {
 		Settings oldSettings =
 				settingsManager.getSettings(txn, SETTINGS_NAMESPACE);
-		int attempts = oldSettings.getInt(SETTINGS_KEY_ATTEMPTS, 0);
+		int newAttempts = 1 + oldSettings.getInt(SETTINGS_KEY_ATTEMPTS, 0);
+		long lastSuccess = oldSettings.getLong(SETTINGS_KEY_LAST_SUCCESS, 0);
 		Settings newSettings = new Settings();
 		newSettings.putLong(SETTINGS_KEY_LAST_ATTEMPT, now);
-		newSettings.putInt(SETTINGS_KEY_ATTEMPTS, attempts + 1);
+		newSettings.putInt(SETTINGS_KEY_ATTEMPTS, newAttempts);
 		settingsManager.mergeSettings(txn, newSettings, SETTINGS_NAMESPACE);
+		List<MailboxVersion> serverSupports = parseServerSupports(oldSettings);
+		MailboxStatus status = new MailboxStatus(now, lastSuccess, newAttempts,
+				serverSupports);
+		txn.attach(new OwnMailboxConnectionStatusEvent(status));
+		if (status.hasProblem(now)) txn.attach(new MailboxProblemEvent());
 	}
 
 	@Override
@@ -113,4 +170,19 @@ class MailboxSettingsManagerImpl implements MailboxSettingsManager {
 		if (isNullOrEmpty(filename)) return null;
 		return filename;
 	}
+
+	private List<MailboxVersion> parseServerSupports(Settings s)
+			throws DbException {
+		if (!s.containsKey(SETTINGS_KEY_SERVER_SUPPORTS)) return emptyList();
+		int[] ints = s.getIntArray(SETTINGS_KEY_SERVER_SUPPORTS);
+		// We know we were paired, so we must have proper serverSupports
+		if (ints == null || ints.length == 0 || ints.length % 2 != 0) {
+			throw new DbException();
+		}
+		List<MailboxVersion> serverSupports = new ArrayList<>();
+		for (int i = 0; i < ints.length - 1; i += 2) {
+			serverSupports.add(new MailboxVersion(ints[i], ints[i + 1]));
+		}
+		return serverSupports;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxUpdateManagerImpl.java

@@ -0,0 +1,373 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.client.ContactGroupFactory;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager.ContactHook;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataParser;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Metadata;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.OpenDatabaseHook;
+import org.briarproject.bramble.api.mailbox.MailboxAuthToken;
+import org.briarproject.bramble.api.mailbox.MailboxFolderId;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.mailbox.MailboxSettingsManager.MailboxHook;
+import org.briarproject.bramble.api.mailbox.MailboxUpdate;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateManager;
+import org.briarproject.bramble.api.mailbox.MailboxUpdateWithMailbox;
+import org.briarproject.bramble.api.mailbox.MailboxVersion;
+import org.briarproject.bramble.api.mailbox.event.RemoteMailboxUpdateEvent;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Group.Visibility;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager.ClientVersioningHook;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
+
+@NotNullByDefault
+class MailboxUpdateManagerImpl implements MailboxUpdateManager,
+		OpenDatabaseHook, ContactHook, ClientVersioningHook,
+		IncomingMessageHook, MailboxHook {
+
+	private final List<MailboxVersion> clientSupports;
+	private final DatabaseComponent db;
+	private final ClientHelper clientHelper;
+	private final ClientVersioningManager clientVersioningManager;
+	private final MetadataParser metadataParser;
+	private final ContactGroupFactory contactGroupFactory;
+	private final Clock clock;
+	private final MailboxSettingsManager mailboxSettingsManager;
+	private final CryptoComponent crypto;
+	private final Group localGroup;
+
+	@Inject
+	MailboxUpdateManagerImpl(List<MailboxVersion> clientSupports,
+			DatabaseComponent db, ClientHelper clientHelper,
+			ClientVersioningManager clientVersioningManager,
+			MetadataParser metadataParser,
+			ContactGroupFactory contactGroupFactory, Clock clock,
+			MailboxSettingsManager mailboxSettingsManager,
+			CryptoComponent crypto) {
+		this.clientSupports = clientSupports;
+		this.db = db;
+		this.clientHelper = clientHelper;
+		this.clientVersioningManager = clientVersioningManager;
+		this.metadataParser = metadataParser;
+		this.contactGroupFactory = contactGroupFactory;
+		this.clock = clock;
+		this.mailboxSettingsManager = mailboxSettingsManager;
+		this.crypto = crypto;
+		localGroup = contactGroupFactory.createLocalGroup(CLIENT_ID,
+				MAJOR_VERSION);
+	}
+
+	@Override
+	public void onDatabaseOpened(Transaction txn) throws DbException {
+		if (db.containsGroup(txn, localGroup.getId())) {
+			try {
+				BdfDictionary meta = clientHelper.getGroupMetadataAsDictionary(
+						txn, localGroup.getId());
+				BdfList sent = meta.getList(GROUP_KEY_SENT_CLIENT_SUPPORTS);
+				if (clientHelper.parseMailboxVersionList(sent)
+						.equals(clientSupports)) {
+					return;
+				}
+			} catch (FormatException e) {
+				throw new DbException();
+			}
+			// Our current clientSupports list has changed compared to what we
+			// last sent out.
+			for (Contact c : db.getContacts(txn)) {
+				MailboxUpdate latest = getLocalUpdate(txn, c.getId());
+				MailboxUpdate updated;
+				if (latest.hasMailbox()) {
+					updated = new MailboxUpdateWithMailbox(
+							(MailboxUpdateWithMailbox) latest, clientSupports);
+				} else {
+					updated = new MailboxUpdate(clientSupports);
+				}
+				Group g = getContactGroup(c);
+				storeMessageReplaceLatest(txn, g.getId(), updated);
+			}
+		} else {
+			db.addGroup(txn, localGroup);
+			// Set things up for any pre-existing contacts
+			for (Contact c : db.getContacts(txn)) {
+				addingContact(txn, c);
+			}
+		}
+
+		try {
+			BdfDictionary meta = BdfDictionary.of(new BdfEntry(
+					GROUP_KEY_SENT_CLIENT_SUPPORTS,
+					encodeSupportsList(clientSupports)));
+			clientHelper.mergeGroupMetadata(txn, localGroup.getId(), meta);
+		} catch (FormatException e) {
+			throw new DbException();
+		}
+	}
+
+	@Override
+	public void addingContact(Transaction txn, Contact c) throws DbException {
+		// Create a group to share with the contact
+		Group g = getContactGroup(c);
+		db.addGroup(txn, g);
+		// Apply the client's visibility to the contact group
+		Visibility client = clientVersioningManager
+				.getClientVisibility(txn, c.getId(), CLIENT_ID, MAJOR_VERSION);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), client);
+		// Attach the contact ID to the group
+		clientHelper.setContactId(txn, g.getId(), c.getId());
+		MailboxProperties ownProps =
+				mailboxSettingsManager.getOwnMailboxProperties(txn);
+		if (ownProps != null) {
+			// We are paired, create and send props to the newly added contact
+			createAndSendUpdateWithMailbox(txn, c, ownProps.getServerSupports(),
+					ownProps.getOnion());
+		} else {
+			// Not paired, but we still want to get our clientSupports sent
+			sendUpdateNoMailbox(txn, c);
+		}
+	}
+
+	@Override
+	public void removingContact(Transaction txn, Contact c) throws DbException {
+		db.removeGroup(txn, getContactGroup(c));
+	}
+
+	@Override
+	public void mailboxPaired(Transaction txn, String ownOnion,
+			List<MailboxVersion> serverSupports) throws DbException {
+		for (Contact c : db.getContacts(txn)) {
+			createAndSendUpdateWithMailbox(txn, c, serverSupports, ownOnion);
+		}
+	}
+
+	@Override
+	public void mailboxUnpaired(Transaction txn) throws DbException {
+		for (Contact c : db.getContacts(txn)) {
+			sendUpdateNoMailbox(txn, c);
+		}
+	}
+
+	@Override
+	public void onClientVisibilityChanging(Transaction txn, Contact c,
+			Visibility v) throws DbException {
+		// Apply the client's visibility to the contact group
+		Group g = getContactGroup(c);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), v);
+	}
+
+	@Override
+	public DeliveryAction incomingMessage(Transaction txn, Message m,
+			Metadata meta) throws DbException, InvalidMessageException {
+		try {
+			BdfDictionary d = metadataParser.parse(meta);
+			// Get latest non-local update in the same group (from same contact)
+			LatestUpdate latest = findLatest(txn, m.getGroupId(), false);
+			if (latest != null) {
+				if (d.getLong(MSG_KEY_VERSION) > latest.version) {
+					db.deleteMessage(txn, latest.messageId);
+					db.deleteMessageMetadata(txn, latest.messageId);
+				} else {
+					// Delete this update, we already have a newer one
+					db.deleteMessage(txn, m.getId());
+					db.deleteMessageMetadata(txn, m.getId());
+					return ACCEPT_DO_NOT_SHARE;
+				}
+			}
+			ContactId c = clientHelper.getContactId(txn, m.getGroupId());
+			BdfList body = clientHelper.getMessageAsList(txn, m.getId());
+			MailboxUpdate u = parseUpdate(body);
+			txn.attach(new RemoteMailboxUpdateEvent(c, u));
+			// Reset message retransmission timers for the contact. Avoiding
+			// messages getting stranded:
+			// - on our mailbox, if they now have a mailbox but didn't before
+			// - on the contact's old mailbox, if they removed their mailbox
+			// - on the contact's old mailbox, if they replaced their mailbox
+			db.resetUnackedMessagesToSend(txn, c);
+		} catch (FormatException e) {
+			throw new InvalidMessageException(e);
+		}
+		return ACCEPT_DO_NOT_SHARE;
+	}
+
+	@Override
+	public MailboxUpdate getLocalUpdate(Transaction txn, ContactId c)
+			throws DbException {
+		MailboxUpdate local = getUpdate(txn, db.getContact(txn, c), true);
+		// An update (with or without mailbox) is created when contact is added
+		if (local == null) {
+			throw new DbException();
+		}
+		return local;
+	}
+
+	@Override
+	@Nullable
+	public MailboxUpdate getRemoteUpdate(Transaction txn, ContactId c)
+			throws DbException {
+		return getUpdate(txn, db.getContact(txn, c), false);
+	}
+
+	/**
+	 * Creates and sends an update message to the given contact. The message
+	 * holds our own mailbox's onion, generated unique properties, and lists of
+	 * supported Mailbox API version(s). All of which the contact needs to
+	 * communicate with our Mailbox.
+	 */
+	private void createAndSendUpdateWithMailbox(Transaction txn, Contact c,
+			List<MailboxVersion> serverSupports, String ownOnion)
+			throws DbException {
+		String baseUrl = "http://" + ownOnion + ".onion"; // TODO
+		MailboxProperties properties = new MailboxProperties(baseUrl,
+				new MailboxAuthToken(crypto.generateUniqueId().getBytes()),
+				serverSupports,
+				new MailboxFolderId(crypto.generateUniqueId().getBytes()),
+				new MailboxFolderId(crypto.generateUniqueId().getBytes()));
+		MailboxUpdate u =
+				new MailboxUpdateWithMailbox(clientSupports, properties);
+		Group g = getContactGroup(c);
+		storeMessageReplaceLatest(txn, g.getId(), u);
+	}
+
+	/**
+	 * Sends an update message with empty properties to the given contact. The
+	 * empty update indicates for the receiving contact that we don't have any
+	 * Mailbox that they can use. It still includes the list of Mailbox API
+	 * version(s) that we support as a client.
+	 */
+	private void sendUpdateNoMailbox(Transaction txn, Contact c)
+			throws DbException {
+		Group g = getContactGroup(c);
+		MailboxUpdate u = new MailboxUpdate(clientSupports);
+		storeMessageReplaceLatest(txn, g.getId(), u);
+	}
+
+	@Nullable
+	private MailboxUpdate getUpdate(Transaction txn, Contact c, boolean local)
+			throws DbException {
+		MailboxUpdate u = null;
+		Group g = getContactGroup(c);
+		try {
+			LatestUpdate latest = findLatest(txn, g.getId(), local);
+			if (latest != null) {
+				BdfList body =
+						clientHelper.getMessageAsList(txn, latest.messageId);
+				u = parseUpdate(body);
+			}
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+		return u;
+	}
+
+	private void storeMessageReplaceLatest(Transaction txn, GroupId g,
+			MailboxUpdate u) throws DbException {
+		try {
+			LatestUpdate latest = findLatest(txn, g, true);
+			long version = latest == null ? 1 : latest.version + 1;
+			Message m = clientHelper.createMessage(g, clock.currentTimeMillis(),
+					encodeProperties(version, u));
+			BdfDictionary meta = new BdfDictionary();
+			meta.put(MSG_KEY_VERSION, version);
+			meta.put(MSG_KEY_LOCAL, true);
+			clientHelper.addLocalMessage(txn, m, meta, true, false);
+			if (latest != null) {
+				db.removeMessage(txn, latest.messageId);
+			}
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	@Nullable
+	private LatestUpdate findLatest(Transaction txn, GroupId g, boolean local)
+			throws DbException, FormatException {
+		Map<MessageId, BdfDictionary> metadata =
+				clientHelper.getMessageMetadataAsDictionary(txn, g);
+		// We should have at most 1 local and 1 remote
+		if (metadata.size() > 2) {
+			throw new IllegalStateException();
+		}
+		for (Entry<MessageId, BdfDictionary> e : metadata.entrySet()) {
+			BdfDictionary meta = e.getValue();
+			if (meta.getBoolean(MSG_KEY_LOCAL) == local) {
+				return new LatestUpdate(e.getKey(),
+						meta.getLong(MSG_KEY_VERSION));
+			}
+		}
+		return null;
+	}
+
+	private BdfList encodeProperties(long version, MailboxUpdate u) {
+		BdfDictionary dict = new BdfDictionary();
+		BdfList serverSupports = new BdfList();
+		if (u.hasMailbox()) {
+			MailboxUpdateWithMailbox um = (MailboxUpdateWithMailbox) u;
+			MailboxProperties properties = um.getMailboxProperties();
+			serverSupports = encodeSupportsList(properties.getServerSupports());
+			dict.put(PROP_KEY_ONION, properties.getOnion());
+			dict.put(PROP_KEY_AUTHTOKEN, properties.getAuthToken());
+			dict.put(PROP_KEY_INBOXID, properties.getInboxId());
+			dict.put(PROP_KEY_OUTBOXID, properties.getOutboxId());
+		}
+		return BdfList.of(version, encodeSupportsList(u.getClientSupports()),
+				serverSupports, dict);
+	}
+
+	private BdfList encodeSupportsList(List<MailboxVersion> supportsList) {
+		BdfList supports = new BdfList();
+		for (MailboxVersion version : supportsList) {
+			supports.add(BdfList.of(version.getMajor(), version.getMinor()));
+		}
+		return supports;
+	}
+
+	private MailboxUpdate parseUpdate(BdfList body) throws FormatException {
+		BdfList clientSupports = body.getList(1);
+		BdfList serverSupports = body.getList(2);
+		BdfDictionary dict = body.getDictionary(3);
+		return clientHelper.parseAndValidateMailboxUpdate(clientSupports,
+				serverSupports, dict);
+	}
+
+	private Group getContactGroup(Contact c) {
+		return contactGroupFactory.createContactGroup(CLIENT_ID, MAJOR_VERSION,
+				c);
+	}
+
+	private static class LatestUpdate {
+
+		private final MessageId messageId;
+		private final long version;
+
+		private LatestUpdate(MessageId messageId, long version) {
+			this.messageId = messageId;
+			this.version = version;
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxUpdateValidator.java

@@ -0,0 +1,54 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.BdfMessageContext;
+import org.briarproject.bramble.api.client.BdfMessageValidator;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.system.Clock;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.MSG_KEY_LOCAL;
+import static org.briarproject.bramble.api.mailbox.MailboxUpdateManager.MSG_KEY_VERSION;
+import static org.briarproject.bramble.util.ValidationUtils.checkSize;
+
+@Immutable
+@NotNullByDefault
+class MailboxUpdateValidator extends BdfMessageValidator {
+
+	MailboxUpdateValidator(ClientHelper clientHelper,
+			MetadataEncoder metadataEncoder, Clock clock) {
+		super(clientHelper, metadataEncoder, clock);
+	}
+
+	@Override
+	protected BdfMessageContext validateMessage(Message m, Group g,
+			BdfList body) throws InvalidMessageException, FormatException {
+		// Version, Properties, clientSupports, serverSupports
+		checkSize(body, 4);
+		// Version
+		long version = body.getLong(0);
+		if (version < 0) throw new FormatException();
+		// clientSupports
+		BdfList clientSupports = body.getList(1);
+		// serverSupports
+		BdfList serverSupports = body.getList(2);
+		// Properties
+		BdfDictionary dictionary = body.getDictionary(3);
+		clientHelper.parseAndValidateMailboxUpdate(clientSupports,
+				serverSupports, dictionary);
+		// Return the metadata
+		BdfDictionary meta = new BdfDictionary();
+		meta.put(MSG_KEY_VERSION, version);
+		meta.put(MSG_KEY_LOCAL, false);
+		return new BdfMessageContext(meta);
+	}
+
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/OwnMailboxConnectivityChecker.java

@@ -0,0 +1,75 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.TransactionManager;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
+
+import java.io.IOException;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@ThreadSafe
+@NotNullByDefault
+class OwnMailboxConnectivityChecker extends ConnectivityCheckerImpl {
+
+	private static final Logger LOG =
+			getLogger(OwnMailboxConnectivityChecker.class.getName());
+
+	private final MailboxApi mailboxApi;
+	private final TransactionManager db;
+	private final MailboxSettingsManager mailboxSettingsManager;
+
+	OwnMailboxConnectivityChecker(Clock clock,
+			MailboxApiCaller mailboxApiCaller,
+			MailboxApi mailboxApi,
+			TransactionManager db,
+			MailboxSettingsManager mailboxSettingsManager) {
+		super(clock, mailboxApiCaller);
+		this.mailboxApi = mailboxApi;
+		this.db = db;
+		this.mailboxSettingsManager = mailboxSettingsManager;
+	}
+
+	@Override
+	ApiCall createConnectivityCheckTask(MailboxProperties properties) {
+		if (!properties.isOwner()) throw new IllegalArgumentException();
+		return () -> {
+			try {
+				return checkConnectivityAndStoreResult(properties);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				return true; // Retry
+			}
+		};
+	}
+
+	private boolean checkConnectivityAndStoreResult(
+			MailboxProperties properties) throws DbException {
+		try {
+			if (!mailboxApi.checkStatus(properties)) throw new ApiException();
+			LOG.info("Own mailbox is reachable");
+			long now = clock.currentTimeMillis();
+			db.transaction(false, txn -> mailboxSettingsManager
+					.recordSuccessfulConnection(txn, now));
+			// Call the observers and cache the result
+			onConnectivityCheckSucceeded(now);
+			return false; // Don't retry
+		} catch (IOException | ApiException e) {
+			LOG.warning("Own mailbox is unreachable");
+			logException(LOG, WARNING, e);
+			long now = clock.currentTimeMillis();
+			db.transaction(false, txn -> mailboxSettingsManager
+					.recordFailedConnectionAttempt(txn, now));
+		}
+		return true; // Retry
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/SimpleApiCall.java

@@ -0,0 +1,39 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
+import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
+
+import java.io.IOException;
+import java.util.logging.Logger;
+
+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.util.LogUtils.logException;
+
+/**
+ * Convenience class for making simple API calls that don't return values.
+ */
+@NotNullByDefault
+public abstract class SimpleApiCall implements ApiCall {
+
+	private static final Logger LOG = getLogger(SimpleApiCall.class.getName());
+
+	abstract void tryToCallApi()
+			throws IOException, ApiException, TolerableFailureException;
+
+	@Override
+	public boolean callApi() {
+		try {
+			tryToCallApi();
+			return false; // Succeeded, don't retry
+		} catch (IOException | ApiException e) {
+			logException(LOG, WARNING, e);
+			return true; // Failed, retry with backoff
+		} catch (TolerableFailureException e) {
+			logException(LOG, INFO, e);
+			return false; // Failed tolerably, don't retry
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/TorReachabilityMonitor.java

@@ -0,0 +1,45 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.concurrent.TimeUnit.MINUTES;
+
+@ThreadSafe
+@NotNullByDefault
+interface TorReachabilityMonitor {
+
+	/**
+	 * How long the Tor plugin needs to be continuously
+	 * {@link Plugin.State#ACTIVE active} before we assume our contacts can
+	 * reach our hidden service.
+	 */
+	long REACHABILITY_PERIOD_MS = MINUTES.toMillis(10);
+
+	/**
+	 * Starts the monitor.
+	 */
+	void start();
+
+	/**
+	 * Destroys the monitor.
+	 */
+	void destroy();
+
+	/**
+	 * Adds an observer that will be called when our Tor hidden service becomes
+	 * reachable. If our hidden service is already reachable, the observer is
+	 * called immediately.
+	 * <p>
+	 * Observers are removed after being called, or when the monitor is
+	 * {@link #destroy() destroyed}.
+	 */
+	void addOneShotObserver(TorReachabilityObserver o);
+
+	interface TorReachabilityObserver {
+
+		void onTorReachable();
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/TorReachabilityMonitorImpl.java

@@ -0,0 +1,129 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.Cancellable;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventBus;
+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.Plugin;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
+import org.briarproject.bramble.api.system.TaskScheduler;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.TorConstants.ID;
+
+@ThreadSafe
+@NotNullByDefault
+class TorReachabilityMonitorImpl
+		implements TorReachabilityMonitor, EventListener {
+
+	private final Executor ioExecutor;
+	private final TaskScheduler taskScheduler;
+	private final PluginManager pluginManager;
+	private final EventBus eventBus;
+	private final Object lock = new Object();
+
+	@GuardedBy("lock")
+	private boolean reachable = false, destroyed = false;
+
+	@GuardedBy("lock")
+	private final List<TorReachabilityObserver> observers = new ArrayList<>();
+
+	@GuardedBy("lock")
+	@Nullable
+	private Cancellable task = null;
+
+	@Inject
+	TorReachabilityMonitorImpl(
+			@IoExecutor Executor ioExecutor,
+			TaskScheduler taskScheduler,
+			PluginManager pluginManager,
+			EventBus eventBus) {
+		this.ioExecutor = ioExecutor;
+		this.taskScheduler = taskScheduler;
+		this.pluginManager = pluginManager;
+		this.eventBus = eventBus;
+	}
+
+	@Override
+	public void start() {
+		eventBus.addListener(this);
+		Plugin plugin = pluginManager.getPlugin(ID);
+		if (plugin != null && plugin.getState() == ACTIVE) onTorActive();
+	}
+
+	@Override
+	public void destroy() {
+		eventBus.removeListener(this);
+		synchronized (lock) {
+			destroyed = true;
+			if (task != null) task.cancel();
+			task = null;
+			observers.clear();
+		}
+	}
+
+	@Override
+	public void addOneShotObserver(TorReachabilityObserver o) {
+		boolean callNow = false;
+		synchronized (lock) {
+			if (destroyed) return;
+			if (reachable) callNow = true;
+			else observers.add(o);
+		}
+		if (callNow) o.onTorReachable();
+	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
+			if (t.getTransportId().equals(ID)) onTorActive();
+		} else if (e instanceof TransportInactiveEvent) {
+			TransportInactiveEvent t = (TransportInactiveEvent) e;
+			if (t.getTransportId().equals(ID)) onTorInactive();
+		}
+	}
+
+	private void onTorActive() {
+		synchronized (lock) {
+			if (destroyed || task != null) return;
+			task = taskScheduler.schedule(this::onTorReachable, ioExecutor,
+					REACHABILITY_PERIOD_MS, MILLISECONDS);
+		}
+	}
+
+	private void onTorInactive() {
+		synchronized (lock) {
+			reachable = false;
+			if (task != null) task.cancel();
+			task = null;
+		}
+	}
+
+	@IoExecutor
+	private void onTorReachable() {
+		List<TorReachabilityObserver> observers;
+		synchronized (lock) {
+			if (destroyed) return;
+			reachable = true;
+			observers = new ArrayList<>(this.observers);
+			this.observers.clear();
+			task = null;
+		}
+		for (TorReachabilityObserver o : observers) o.onTorReachable();
+	}
+}

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.Cancellable;
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
@@ -27,7 +28,6 @@ import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.TaskScheduler;
-import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
 import org.briarproject.bramble.api.system.Wakeful;
 import org.briarproject.bramble.api.system.WakefulIoExecutor;
 

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

@@ -67,6 +67,7 @@ abstract class AbstractRemovableDrivePlugin implements SimplexPlugin {
 	public void start() {
 		callback.mergeLocalProperties(
 				new TransportProperties(singletonMap(PROP_SUPPORTED, "true")));
+		callback.pluginStateChanged(ACTIVE);
 	}
 
 	@Override

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

@@ -11,6 +11,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
@@ -29,11 +30,6 @@ abstract class FilePlugin implements SimplexPlugin {
 	protected final PluginCallback callback;
 	protected final long maxLatency;
 
-	protected abstract void writerFinished(File f, boolean exception);
-
-	protected abstract void readerFinished(File f, boolean exception,
-			boolean recognised);
-
 	FilePlugin(PluginCallback callback, long maxLatency) {
 		this.callback = callback;
 		this.maxLatency = maxLatency;
@@ -50,9 +46,8 @@ abstract class FilePlugin implements SimplexPlugin {
 		String path = p.get(PROP_PATH);
 		if (isNullOrEmpty(path)) return null;
 		try {
-			File file = new File(path);
-			FileInputStream in = new FileInputStream(file);
-			return new FileTransportReader(file, in, this);
+			FileInputStream in = new FileInputStream(path);
+			return new TransportInputStreamReader(in);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
 			return null;
@@ -70,8 +65,8 @@ abstract class FilePlugin implements SimplexPlugin {
 				LOG.info("Failed to create file");
 				return null;
 			}
-			FileOutputStream out = new FileOutputStream(file);
-			return new FileTransportWriter(file, out, this);
+			OutputStream out = new FileOutputStream(file);
+			return new TransportOutputStreamWriter(this, out);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
 			return null;

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

@@ -1,39 +0,0 @@
-package org.briarproject.bramble.plugin.file;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportConnectionReader;
-
-import java.io.File;
-import java.io.InputStream;
-import java.util.logging.Logger;
-
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.IoUtils.tryToClose;
-
-@NotNullByDefault
-class FileTransportReader implements TransportConnectionReader {
-
-	private static final Logger LOG =
-			Logger.getLogger(FileTransportReader.class.getName());
-
-	private final File file;
-	private final InputStream in;
-	private final FilePlugin plugin;
-
-	FileTransportReader(File file, InputStream in, FilePlugin plugin) {
-		this.file = file;
-		this.in = in;
-		this.plugin = plugin;
-	}
-
-	@Override
-	public InputStream getInputStream() {
-		return in;
-	}
-
-	@Override
-	public void dispose(boolean exception, boolean recognised) {
-		tryToClose(in, LOG, WARNING);
-		plugin.readerFinished(file, exception, recognised);
-	}
-}

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

@@ -1,54 +0,0 @@
-package org.briarproject.bramble.plugin.file;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
-
-import java.io.File;
-import java.io.OutputStream;
-import java.util.logging.Logger;
-
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.IoUtils.tryToClose;
-
-@NotNullByDefault
-class FileTransportWriter implements TransportConnectionWriter {
-
-	private static final Logger LOG =
-			Logger.getLogger(FileTransportWriter.class.getName());
-
-	private final File file;
-	private final OutputStream out;
-	private final FilePlugin plugin;
-
-	FileTransportWriter(File file, OutputStream out, FilePlugin plugin) {
-		this.file = file;
-		this.out = out;
-		this.plugin = plugin;
-	}
-
-	@Override
-	public long getMaxLatency() {
-		return plugin.getMaxLatency();
-	}
-
-	@Override
-	public int getMaxIdleTime() {
-		return plugin.getMaxIdleTime();
-	}
-
-	@Override
-	public boolean isLossyAndCheap() {
-		return plugin.isLossyAndCheap();
-	}
-
-	@Override
-	public OutputStream getOutputStream() {
-		return out;
-	}
-
-	@Override
-	public void dispose(boolean exception) {
-		tryToClose(out, LOG, WARNING);
-		plugin.writerFinished(file, exception);
-	}
-}

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

@@ -0,0 +1,73 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.ConnectionHandler;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.PluginException;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.util.Collection;
+
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+
+@NotNullByDefault
+class MailboxPlugin extends FilePlugin {
+
+	MailboxPlugin(PluginCallback callback, long maxLatency) {
+		super(callback, maxLatency);
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public int getMaxIdleTime() {
+		// Unused for simplex transports
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void start() throws PluginException {
+		callback.pluginStateChanged(ACTIVE);
+	}
+
+	@Override
+	public void stop() throws PluginException {
+	}
+
+	@Override
+	public State getState() {
+		return ACTIVE;
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return 0;
+	}
+
+	@Override
+	public boolean shouldPoll() {
+		return false;
+	}
+
+	@Override
+	public int getPollingInterval() {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void poll(
+			Collection<Pair<TransportProperties, ConnectionHandler>> properties) {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public boolean isLossyAndCheap() {
+		return false;
+	}
+}

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

@@ -0,0 +1,39 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+
+@NotNullByDefault
+public class MailboxPluginFactory implements SimplexPluginFactory {
+
+	private static final long MAX_LATENCY = DAYS.toMillis(14);
+
+	@Inject
+	MailboxPluginFactory() {
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public long getMaxLatency() {
+		return MAX_LATENCY;
+	}
+
+	@Nullable
+	@Override
+	public SimplexPlugin createPlugin(PluginCallback callback) {
+		return new MailboxPlugin(callback, MAX_LATENCY);
+	}
+}

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

@@ -11,6 +11,7 @@ public interface CircumventionProvider {
 	enum BridgeType {
 		DEFAULT_OBFS4,
 		NON_DEFAULT_OBFS4,
+		VANILLA,
 		MEEK
 	}
 
@@ -20,30 +21,30 @@ public interface CircumventionProvider {
 	 * See https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
 	 * and https://trac.torproject.org/projects/tor/wiki/doc/OONI/censorshipwiki
 	 */
-	String[] BLOCKED = {"CN", "IR", "EG", "BY", "TR", "SY", "VE", "RU"};
+	String[] BLOCKED = {"BY", "CN", "EG", "IR", "RU", "TM", "VE"};
 
 	/**
-	 * Countries where obfs4 or meek bridge connections are likely to work.
+	 * Countries where bridge connections are likely to work.
 	 * Should be a subset of {@link #BLOCKED} and the union of
-	 * {@link #DEFAULT_OBFS4_BRIDGES}, {@link #NON_DEFAULT_OBFS4_BRIDGES} and
+	 * {@link #DEFAULT_BRIDGES}, {@link #NON_DEFAULT_BRIDGES} and
 	 * {@link #MEEK_BRIDGES}.
 	 */
-	String[] BRIDGES = {"CN", "IR", "EG", "BY", "TR", "SY", "VE", "RU"};
+	String[] BRIDGES = {"BY", "CN", "EG", "IR", "RU", "TM", "VE"};
 
 	/**
-	 * Countries where default obfs4 bridges are likely to work.
+	 * Countries where default obfs4 or vanilla bridges are likely to work.
 	 * Should be a subset of {@link #BRIDGES}.
 	 */
-	String[] DEFAULT_OBFS4_BRIDGES = {"EG", "BY", "TR", "SY", "VE"};
+	String[] DEFAULT_BRIDGES = {"EG", "VE"};
 
 	/**
-	 * Countries where non-default obfs4 bridges are likely to work.
+	 * Countries where non-default obfs4 or vanilla bridges are likely to work.
 	 * Should be a subset of {@link #BRIDGES}.
 	 */
-	String[] NON_DEFAULT_OBFS4_BRIDGES = {"RU"};
+	String[] NON_DEFAULT_BRIDGES = {"BY", "RU", "TM"};
 
 	/**
-	 * Countries where obfs4 bridges won't work and meek is needed.
+	 * Countries where obfs4 and vanilla bridges won't work and meek is needed.
 	 * Should be a subset of {@link #BRIDGES}.
 	 */
 	String[] MEEK_BRIDGES = {"CN", "IR"};
@@ -60,10 +61,11 @@ public interface CircumventionProvider {
 	boolean doBridgesWork(String countryCode);
 
 	/**
-	 * Returns the best type of bridge connection for the given country, or
-	 * {@link #DEFAULT_OBFS4_BRIDGES} if no bridge type is known to work.
+	 * Returns the types of bridge connection that are suitable for the given
+	 * country, or {@link #DEFAULT_BRIDGES} if no bridge type is known
+	 * to work.
 	 */
-	BridgeType getBestBridgeType(String countryCode);
+	List<BridgeType> getSuitableBridgeTypes(String countryCode);
 
 	@IoExecutor
 	List<String> getBridges(BridgeType type);

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

@@ -14,10 +14,12 @@ import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static java.util.Arrays.asList;
+import static java.util.Collections.singletonList;
 import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.DEFAULT_OBFS4;
 import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.MEEK;
 import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.NON_DEFAULT_OBFS4;
+import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.VANILLA;
 
 @Immutable
 @NotNullByDefault
@@ -30,9 +32,9 @@ class CircumventionProviderImpl implements CircumventionProvider {
 	private static final Set<String> BRIDGE_COUNTRIES =
 			new HashSet<>(asList(BRIDGES));
 	private static final Set<String> DEFAULT_OBFS4_BRIDGE_COUNTRIES =
-			new HashSet<>(asList(DEFAULT_OBFS4_BRIDGES));
-	private static final Set<String> NON_DEFAULT_OBFS4_BRIDGE_COUNTRIES =
-			new HashSet<>(asList(NON_DEFAULT_OBFS4_BRIDGES));
+			new HashSet<>(asList(DEFAULT_BRIDGES));
+	private static final Set<String> NON_DEFAULT_BRIDGE_COUNTRIES =
+			new HashSet<>(asList(NON_DEFAULT_BRIDGES));
 	private static final Set<String> MEEK_COUNTRIES =
 			new HashSet<>(asList(MEEK_BRIDGES));
 
@@ -51,15 +53,15 @@ class CircumventionProviderImpl implements CircumventionProvider {
 	}
 
 	@Override
-	public BridgeType getBestBridgeType(String countryCode) {
+	public List<BridgeType> getSuitableBridgeTypes(String countryCode) {
 		if (DEFAULT_OBFS4_BRIDGE_COUNTRIES.contains(countryCode)) {
-			return DEFAULT_OBFS4;
-		} else if (NON_DEFAULT_OBFS4_BRIDGE_COUNTRIES.contains(countryCode)) {
-			return NON_DEFAULT_OBFS4;
+			return asList(DEFAULT_OBFS4, VANILLA);
+		} else if (NON_DEFAULT_BRIDGE_COUNTRIES.contains(countryCode)) {
+			return asList(NON_DEFAULT_OBFS4, VANILLA);
 		} else if (MEEK_COUNTRIES.contains(countryCode)) {
-			return MEEK;
+			return singletonList(MEEK);
 		} else {
-			return DEFAULT_OBFS4;
+			return asList(DEFAULT_OBFS4, VANILLA);
 		}
 	}
 
@@ -73,12 +75,10 @@ class CircumventionProviderImpl implements CircumventionProvider {
 		List<String> bridges = new ArrayList<>();
 		while (scanner.hasNextLine()) {
 			String line = scanner.nextLine();
-			boolean isDefaultObfs4 = line.startsWith("d ");
-			boolean isNonDefaultObfs4 = line.startsWith("n ");
-			boolean isMeek = line.startsWith("m ");
-			if ((type == DEFAULT_OBFS4 && isDefaultObfs4) ||
-					(type == NON_DEFAULT_OBFS4 && isNonDefaultObfs4) ||
-					(type == MEEK && isMeek)) {
+			if ((type == DEFAULT_OBFS4 && line.startsWith("d ")) ||
+					(type == NON_DEFAULT_OBFS4 && line.startsWith("n ")) ||
+					(type == VANILLA && line.startsWith("v ")) ||
+					(type == MEEK && line.startsWith("m "))) {
 				bridges.add(line.substring(2));
 			}
 		}

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

@@ -2,6 +2,7 @@ package org.briarproject.bramble.plugin.tor;
 
 import net.freehaven.tor.control.EventHandler;
 import net.freehaven.tor.control.TorControlConnection;
+import net.freehaven.tor.control.TorNotRunningException;
 
 import org.briarproject.bramble.PoliteExecutor;
 import org.briarproject.bramble.api.Pair;
@@ -85,7 +86,6 @@ import static org.briarproject.bramble.api.plugin.TorConstants.ID;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_MOBILE;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_AUTOMATIC;
-import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_NEVER;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_WITH_BRIDGES;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_ONLY_WHEN_CHARGING;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_PORT;
@@ -93,7 +93,9 @@ 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.CircumventionProvider.BridgeType.DEFAULT_OBFS4;
 import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.MEEK;
+import static org.briarproject.bramble.plugin.tor.CircumventionProvider.BridgeType.NON_DEFAULT_OBFS4;
 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;
@@ -108,7 +110,14 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private static final Logger LOG = getLogger(TorPlugin.class.getName());
 
 	private static final String[] EVENTS = {
-			"CIRC", "ORCONN", "HS_DESC", "NOTICE", "WARN", "ERR"
+			"CIRC",
+			"ORCONN",
+			"STATUS_GENERAL",
+			"STATUS_CLIENT",
+			"HS_DESC",
+			"NOTICE",
+			"WARN",
+			"ERR"
 	};
 	private static final String OWNER = "__OwningControllerProcess";
 	private static final int COOKIE_TIMEOUT_MS = 3000;
@@ -228,7 +237,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			}
 		}
 		// Load the settings
-		settings = migrateSettings(callback.getSettings());
+		settings = callback.getSettings();
 		// Install or update the assets if necessary
 		if (!assetsAreUpToDate()) installAssets();
 		if (cookieFile.exists() && !cookieFile.delete())
@@ -302,11 +311,19 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			controlConnection.setEventHandler(this);
 			controlConnection.setEvents(asList(EVENTS));
 			// Check whether Tor has already bootstrapped
-			String phase = controlConnection.getInfo("status/bootstrap-phase");
-			if (phase != null && phase.contains("PROGRESS=100")) {
+			String info = controlConnection.getInfo("status/bootstrap-phase");
+			if (info != null && info.contains("PROGRESS=100")) {
 				LOG.info("Tor has already bootstrapped");
 				state.setBootstrapped();
 			}
+			// Check whether Tor has already built a circuit
+			info = controlConnection.getInfo("status/circuit-established");
+			if ("1".equals(info)) {
+				LOG.info("Tor has already built a circuit");
+				state.getAndSetCircuitBuilt(true);
+			}
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
 		} catch (IOException e) {
 			throw new PluginException(e);
 		}
@@ -318,18 +335,6 @@ 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,
-				DEFAULT_PREF_TOR_NETWORK);
-		if (network == PREF_TOR_NETWORK_NEVER) {
-			settings.putInt(PREF_TOR_NETWORK, DEFAULT_PREF_TOR_NETWORK);
-			settings.putBoolean(PREF_PLUGIN_ENABLE, false);
-			callback.mergeSettings(settings);
-		}
-		return settings;
-	}
-
 	private boolean assetsAreUpToDate() {
 		return doneFile.lastModified() > getLastUpdateTime();
 	}
@@ -339,9 +344,14 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			// The done file may already exist from a previous installation
 			//noinspection ResultOfMethodCallIgnored
 			doneFile.delete();
+			// The GeoIP file may exist from a previous installation - we can
+			// save some space by deleting it.
+			// TODO: Remove after a reasonable migration period
+			//  (added 2022-03-29)
+			//noinspection ResultOfMethodCallIgnored
+			geoIpFile.delete();
 			installTorExecutable();
 			installObfs4Executable();
-			extract(getGeoIpInputStream(), geoIpFile);
 			extract(getConfigInputStream(), configFile);
 			if (!doneFile.createNewFile())
 				LOG.warning("Failed to create done file");
@@ -379,14 +389,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		return zin;
 	}
 
-	private InputStream getGeoIpInputStream() throws IOException {
-		InputStream in = resourceProvider.getResourceInputStream("geoip",
-				".zip");
-		ZipInputStream zin = new ZipInputStream(in);
-		if (zin.getNextEntry() == null) throw new IOException();
-		return zin;
-	}
-
 	private InputStream getObfs4InputStream() throws IOException {
 		InputStream in = resourceProvider
 				.getResourceInputStream("obfs4proxy_" + architecture, ".zip");
@@ -493,6 +495,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			} else {
 				response = controlConnection.addOnion(privKey, portLines);
 			}
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
 			return;
@@ -541,26 +545,38 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	protected void enableNetwork(boolean enable) throws IOException {
 		state.enableNetwork(enable);
-		controlConnection.setConf("DisableNetwork", enable ? "0" : "1");
+		try {
+			controlConnection.setConf("DisableNetwork", enable ? "0" : "1");
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
+		}
 	}
 
-	private void enableBridges(boolean enable, BridgeType bridgeType)
+	private void enableBridges(boolean enable, List<BridgeType> bridgeTypes)
 			throws IOException {
-		if (enable) {
-			Collection<String> conf = new ArrayList<>();
-			conf.add("UseBridges 1");
-			File obfs4File = getObfs4ExecutableFile();
-			if (bridgeType == MEEK) {
-				conf.add("ClientTransportPlugin meek_lite exec " +
-						obfs4File.getAbsolutePath());
+		try {
+			if (enable) {
+				Collection<String> conf = new ArrayList<>();
+				conf.add("UseBridges 1");
+				File obfs4File = getObfs4ExecutableFile();
+				if (bridgeTypes.contains(MEEK)) {
+					conf.add("ClientTransportPlugin meek_lite exec " +
+							obfs4File.getAbsolutePath());
+				}
+				if (bridgeTypes.contains(DEFAULT_OBFS4) ||
+						bridgeTypes.contains(NON_DEFAULT_OBFS4)) {
+					conf.add("ClientTransportPlugin obfs4 exec " +
+							obfs4File.getAbsolutePath());
+				}
+				for (BridgeType bridgeType : bridgeTypes) {
+					conf.addAll(circumventionProvider.getBridges(bridgeType));
+				}
+				controlConnection.setConf(conf);
 			} else {
-				conf.add("ClientTransportPlugin obfs4 exec " +
-						obfs4File.getAbsolutePath());
+				controlConnection.setConf("UseBridges", "0");
 			}
-			conf.addAll(circumventionProvider.getBridges(bridgeType));
-			controlConnection.setConf(conf);
-		} else {
-			controlConnection.setConf("UseBridges", "0");
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
 		}
 	}
 
@@ -574,6 +590,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				controlConnection.setConf("DisableNetwork", "1");
 				controlConnection.shutdownTor("TERM");
 				controlSocket.close();
+			} catch (TorNotRunningException e) {
+				throw new RuntimeException(e);
 			} catch (IOException e) {
 				logException(LOG, WARNING, e);
 			}
@@ -646,7 +664,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		} catch (IOException e) {
 			if (LOG.isLoggable(INFO)) {
 				LOG.info("Could not connect to v3 "
-						+ scrubOnion(onion3) + ": " + e.toString());
+						+ scrubOnion(onion3) + ": " + e);
 			}
 			tryToClose(s, LOG, WARNING);
 			return null;
@@ -682,8 +700,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		byte[] localSeed = alice ? aliceSeed : bobSeed;
 		byte[] remoteSeed = alice ? bobSeed : aliceSeed;
 		String blob = torRendezvousCrypto.getPrivateKeyBlob(localSeed);
-		String localOnion = torRendezvousCrypto.getOnionAddress(localSeed);
-		String remoteOnion = torRendezvousCrypto.getOnionAddress(remoteSeed);
+		String localOnion = torRendezvousCrypto.getOnion(localSeed);
+		String remoteOnion = torRendezvousCrypto.getOnion(remoteSeed);
 		TransportProperties remoteProperties = new TransportProperties();
 		remoteProperties.put(PROP_ONION_V3, remoteOnion);
 		try {
@@ -705,7 +723,11 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			});
 			Map<Integer, String> portLines =
 					singletonMap(80, "127.0.0.1:" + port);
-			controlConnection.addOnion(blob, portLines);
+			try {
+				controlConnection.addOnion(blob, portLines);
+			} catch (TorNotRunningException e) {
+				throw new RuntimeException(e);
+			}
 			return new RendezvousEndpoint() {
 
 				@Override
@@ -715,7 +737,11 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 				@Override
 				public void close() throws IOException {
-					controlConnection.delOnion(localOnion);
+					try {
+						controlConnection.delOnion(localOnion);
+					} catch (TorNotRunningException e) {
+						throw new RuntimeException(e);
+					}
 					tryToClose(ss, LOG, WARNING);
 				}
 			};
@@ -727,9 +753,10 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public void circuitStatus(String status, String id, String path) {
-		if (status.equals("BUILT") &&
-				state.getAndSetCircuitBuilt()) {
-			LOG.info("First circuit built");
+		// In case of races between receiving CIRCUIT_ESTABLISHED and setting
+		// DisableNetwork, set our circuitBuilt flag if not already set
+		if (status.equals("BUILT") && !state.getAndSetCircuitBuilt(true)) {
+			LOG.info("Circuit built");
 			backoff.reset();
 		}
 	}
@@ -740,13 +767,10 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public void orConnStatus(String status, String orName) {
-		if (LOG.isLoggable(INFO))
-			LOG.info("OR connection " + status + " " + orName);
-		if (status.equals("CLOSED") || status.equals("FAILED")) {
-			// Check whether we've lost connectivity
-			updateConnectionStatus(networkManager.getNetworkStatus(),
-					batteryManager.isCharging());
-		}
+		if (LOG.isLoggable(INFO)) LOG.info("OR connection " + status);
+
+		if (status.equals("CONNECTED")) state.onOrConnectionConnected();
+		else if (status.equals("CLOSED")) state.onOrConnectionClosed();
 	}
 
 	@Override
@@ -760,24 +784,78 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	@Override
 	public void message(String severity, String msg) {
 		if (LOG.isLoggable(INFO)) LOG.info(severity + " " + msg);
-		if (severity.equals("NOTICE") && msg.startsWith("Bootstrapped 100%")) {
-			state.setBootstrapped();
-			backoff.reset();
-		}
 	}
 
 	@Override
 	public void unrecognized(String type, String msg) {
-		if (type.equals("HS_DESC") && msg.startsWith("UPLOADED")) {
-			if (LOG.isLoggable(INFO)) {
-				String[] words = msg.split(" ");
-				if (words.length > 1 && ONION_V3.matcher(words[1]).matches()) {
-					LOG.info("V3 descriptor uploaded");
-				} else {
-					LOG.info("V2 descriptor uploaded");
+		if (type.equals("STATUS_CLIENT")) {
+			handleClientStatus(removeSeverity(msg));
+		} else if (type.equals("STATUS_GENERAL")) {
+			handleGeneralStatus(removeSeverity(msg));
+		} else if (type.equals("HS_DESC") && msg.startsWith("UPLOADED")) {
+			String[] parts = msg.split(" ");
+			if (parts.length < 2) {
+				LOG.warning("Failed to parse HS_DESC UPLOADED event");
+			} else if (LOG.isLoggable(INFO)) {
+				LOG.info("V3 descriptor uploaded for " + scrubOnion(parts[1]));
+			}
+		}
+	}
+
+	private String removeSeverity(String msg) {
+		return msg.replaceFirst("[^ ]+ ", "");
+	}
+
+	private void handleClientStatus(String msg) {
+		if (msg.startsWith("BOOTSTRAP PROGRESS=100")) {
+			LOG.info("Bootstrapped");
+			state.setBootstrapped();
+			backoff.reset();
+		} else if (msg.startsWith("CIRCUIT_ESTABLISHED")) {
+			if (!state.getAndSetCircuitBuilt(true)) {
+				LOG.info("Circuit built");
+				backoff.reset();
+			}
+		} else if (msg.startsWith("CIRCUIT_NOT_ESTABLISHED")) {
+			if (state.getAndSetCircuitBuilt(false)) {
+				LOG.info("Circuit not built");
+				// TODO: Disable and re-enable network to prompt Tor to rebuild
+				//  its guard/bridge connections? This will also close any
+				//  established circuits, which might still be functioning
+			}
+		}
+	}
+
+	private void handleGeneralStatus(String msg) {
+		if (msg.startsWith("CLOCK_JUMPED")) {
+			Long time = parseLongArgument(msg, "TIME");
+			if (time != null && LOG.isLoggable(WARNING)) {
+				LOG.warning("Clock jumped " + time + " seconds");
+			}
+		} else if (msg.startsWith("CLOCK_SKEW")) {
+			Long skew = parseLongArgument(msg, "SKEW");
+			if (skew != null && LOG.isLoggable(WARNING)) {
+				LOG.warning("Clock is skewed by " + skew + " seconds");
+			}
+		}
+	}
+
+	@Nullable
+	private Long parseLongArgument(String msg, String argName) {
+		String[] args = msg.split(" ");
+		for (String arg : args) {
+			if (arg.startsWith(argName + "=")) {
+				try {
+					return Long.parseLong(arg.substring(argName.length() + 1));
+				} catch (NumberFormatException e) {
+					break;
 				}
 			}
 		}
+		if (LOG.isLoggable(WARNING)) {
+			LOG.warning("Failed to parse " + argName + " from '" + msg + "'");
+		}
+		return null;
 	}
 
 	@Override
@@ -787,11 +865,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			if (s.getNamespace().equals(ID.getString())) {
 				LOG.info("Tor settings updated");
 				settings = s.getSettings();
-				// Works around a bug introduced in Tor 0.3.4.8.
-				// https://trac.torproject.org/projects/tor/ticket/28027
-				// Could be replaced with callback.transportDisabled()
-				// when fixed.
-				disableNetwork();
 				updateConnectionStatus(networkManager.getNetworkStatus(),
 						batteryManager.isCharging());
 			}
@@ -804,16 +877,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		}
 	}
 
-	private void disableNetwork() {
-		connectionStatusExecutor.execute(() -> {
-			try {
-				if (state.isTorRunning()) enableNetwork(false);
-			} catch (IOException ex) {
-				logException(LOG, WARNING, ex);
-			}
-		});
-	}
-
 	private void updateConnectionStatus(NetworkStatus status,
 			boolean charging) {
 		connectionStatusExecutor.execute(() -> {
@@ -847,8 +910,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			int reasonsDisabled = 0;
 			boolean enableNetwork = false, enableBridges = false;
 			boolean enableConnectionPadding = false;
-			BridgeType bridgeType =
-					circumventionProvider.getBestBridgeType(country);
+			List<BridgeType> bridgeTypes =
+					circumventionProvider.getSuitableBridgeTypes(country);
 
 			if (!online) {
 				LOG.info("Disabling network, device is offline");
@@ -877,10 +940,10 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 					enableNetwork = true;
 					if (network == PREF_TOR_NETWORK_WITH_BRIDGES ||
 							(automatic && bridgesWork)) {
-						if (ipv6Only) bridgeType = MEEK;
+						if (ipv6Only) bridgeTypes = singletonList(MEEK);
 						enableBridges = true;
 						if (LOG.isLoggable(INFO)) {
-							LOG.info("Using bridge type " + bridgeType);
+							LOG.info("Using bridge types " + bridgeTypes);
 						}
 					} else {
 						LOG.info("Not using bridges");
@@ -898,7 +961,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 			try {
 				if (enableNetwork) {
-					enableBridges(enableBridges, bridgeType);
+					enableBridges(enableBridges, bridgeTypes);
 					enableConnectionPadding(enableConnectionPadding);
 					useIpv6(ipv6Only);
 				}
@@ -910,12 +973,20 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void enableConnectionPadding(boolean enable) throws IOException {
-		controlConnection.setConf("ConnectionPadding", enable ? "1" : "0");
+		try {
+			controlConnection.setConf("ConnectionPadding", enable ? "1" : "0");
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
+		}
 	}
 
 	private void useIpv6(boolean ipv6Only) throws IOException {
-		controlConnection.setConf("ClientUseIPv4", ipv6Only ? "0" : "1");
-		controlConnection.setConf("ClientUseIPv6", ipv6Only ? "1" : "0");
+		try {
+			controlConnection.setConf("ClientUseIPv4", ipv6Only ? "0" : "1");
+			controlConnection.setConf("ClientUseIPv6", ipv6Only ? "1" : "0");
+		} catch (TorNotRunningException e) {
+			throw new RuntimeException(e);
+		}
 	}
 
 	@ThreadSafe
@@ -938,11 +1009,15 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		@Nullable
 		private ServerSocket serverSocket = null;
 
+		@GuardedBy("this")
+		private int orConnectionsConnected = 0;
+
 		private synchronized void setStarted() {
 			started = true;
 			callback.pluginStateChanged(getState());
 		}
 
+		@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 		private synchronized boolean isTorRunning() {
 			return started && !stopped;
 		}
@@ -961,11 +1036,11 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			callback.pluginStateChanged(getState());
 		}
 
-		private synchronized boolean getAndSetCircuitBuilt() {
-			boolean firstCircuit = !circuitBuilt;
-			circuitBuilt = true;
-			callback.pluginStateChanged(getState());
-			return firstCircuit;
+		private synchronized boolean getAndSetCircuitBuilt(boolean built) {
+			boolean old = circuitBuilt;
+			circuitBuilt = built;
+			if (built != old) callback.pluginStateChanged(getState());
+			return old;
 		}
 
 		private synchronized void enableNetwork(boolean enable) {
@@ -1000,11 +1075,39 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			if (reasonsDisabled != 0) return DISABLED;
 			if (!networkInitialised) return ENABLING;
 			if (!networkEnabled) return INACTIVE;
-			return bootstrapped && circuitBuilt ? ACTIVE : ENABLING;
+			return bootstrapped && circuitBuilt && orConnectionsConnected > 0
+					? ACTIVE : ENABLING;
 		}
 
 		private synchronized int getReasonsDisabled() {
 			return getState() == DISABLED ? reasonsDisabled : 0;
 		}
+
+		private synchronized void onOrConnectionConnected() {
+			int oldConnected = orConnectionsConnected;
+			orConnectionsConnected++;
+			logOrConnections();
+			if (oldConnected == 0) callback.pluginStateChanged(getState());
+		}
+
+		private synchronized void onOrConnectionClosed() {
+			int oldConnected = orConnectionsConnected;
+			orConnectionsConnected--;
+			if (orConnectionsConnected < 0) {
+				LOG.warning("Count was zero before connection closed");
+				orConnectionsConnected = 0;
+			}
+			logOrConnections();
+			if (orConnectionsConnected == 0 && oldConnected != 0) {
+				callback.pluginStateChanged(getState());
+			}
+		}
+
+		@GuardedBy("this")
+		private void logOrConnections() {
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(orConnectionsConnected + " OR connections connected");
+			}
+		}
 	}
 }

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

@@ -0,0 +1,134 @@
+package org.briarproject.bramble.plugin.tor;
+
+import org.briarproject.bramble.api.battery.BatteryManager;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.network.NetworkManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Backoff;
+import org.briarproject.bramble.api.plugin.BackoffFactory;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.TorConstants;
+import org.briarproject.bramble.api.plugin.TorControlPort;
+import org.briarproject.bramble.api.plugin.TorDirectory;
+import org.briarproject.bramble.api.plugin.TorSocksPort;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.LocationUtils;
+import org.briarproject.bramble.api.system.ResourceProvider;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
+
+import java.io.File;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.net.SocketFactory;
+
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+
+@Immutable
+@NotNullByDefault
+abstract class TorPluginFactory implements DuplexPluginFactory {
+
+	protected static final Logger LOG =
+			getLogger(TorPluginFactory.class.getName());
+
+	protected static final int MAX_LATENCY = 30 * 1000; // 30 seconds
+	protected static final int MAX_IDLE_TIME = 30 * 1000; // 30 seconds
+	private static final int MIN_POLLING_INTERVAL = 60 * 1000; // 1 minute
+	private static final int MAX_POLLING_INTERVAL = 10 * 60 * 1000; // 10 mins
+	private static final double BACKOFF_BASE = 1.2;
+
+	protected final Executor ioExecutor, wakefulIoExecutor;
+	protected final NetworkManager networkManager;
+	protected final LocationUtils locationUtils;
+	protected final EventBus eventBus;
+	protected final SocketFactory torSocketFactory;
+	protected final BackoffFactory backoffFactory;
+	protected final ResourceProvider resourceProvider;
+	protected final CircumventionProvider circumventionProvider;
+	protected final BatteryManager batteryManager;
+	protected final Clock clock;
+	protected final CryptoComponent crypto;
+	protected final File torDirectory;
+	protected final int torSocksPort;
+	protected final int torControlPort;
+
+	TorPluginFactory(@IoExecutor Executor ioExecutor,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			EventBus eventBus,
+			SocketFactory torSocketFactory,
+			BackoffFactory backoffFactory,
+			ResourceProvider resourceProvider,
+			CircumventionProvider circumventionProvider,
+			BatteryManager batteryManager,
+			Clock clock,
+			CryptoComponent crypto,
+			@TorDirectory File torDirectory,
+			@TorSocksPort int torSocksPort,
+			@TorControlPort int torControlPort) {
+		this.ioExecutor = ioExecutor;
+		this.wakefulIoExecutor = wakefulIoExecutor;
+		this.networkManager = networkManager;
+		this.locationUtils = locationUtils;
+		this.eventBus = eventBus;
+		this.torSocketFactory = torSocketFactory;
+		this.backoffFactory = backoffFactory;
+		this.resourceProvider = resourceProvider;
+		this.circumventionProvider = circumventionProvider;
+		this.batteryManager = batteryManager;
+		this.clock = clock;
+		this.crypto = crypto;
+		this.torDirectory = torDirectory;
+		this.torSocksPort = torSocksPort;
+		this.torControlPort = torControlPort;
+	}
+
+	@Nullable
+	abstract String getArchitectureForTorBinary();
+
+	abstract TorPlugin createPluginInstance(Backoff backoff,
+			TorRendezvousCrypto torRendezvousCrypto, PluginCallback callback,
+			String architecture);
+
+	@Override
+	public TransportId getId() {
+		return TorConstants.ID;
+	}
+
+	@Override
+	public long getMaxLatency() {
+		return MAX_LATENCY;
+	}
+
+	@Override
+	public DuplexPlugin createPlugin(PluginCallback callback) {
+		// Check that we have a Tor binary for this architecture
+		String architecture = getArchitectureForTorBinary();
+		if (architecture == null) {
+			LOG.warning("Tor is not supported on this architecture");
+			return null;
+		}
+
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("The selected architecture for Tor is " + architecture);
+		}
+
+		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
+				MAX_POLLING_INTERVAL, BACKOFF_BASE);
+		TorRendezvousCrypto torRendezvousCrypto =
+				new TorRendezvousCryptoImpl(crypto);
+		TorPlugin plugin = createPluginInstance(backoff, torRendezvousCrypto,
+				callback, architecture);
+		eventBus.addListener(plugin);
+		return plugin;
+	}
+}

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

@@ -4,7 +4,7 @@ interface TorRendezvousCrypto {
 
 	static final int SEED_BYTES = 32;
 
-	String getOnionAddress(byte[] seed);
+	String getOnion(byte[] seed);
 
 	String getPrivateKeyBlob(byte[] seed);
 }