Add executor with high and low priority queues.

Add a setting to disable Tor when running on battery

Closes #978

See merge request briar/briar!1032

.idea/runConfigurations/All_in_briar_headless.xml

@@ -3,7 +3,7 @@
     <module name="briar-headless" />
     <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="false" />
     <option name="ALTERNATIVE_JRE_PATH" />
-    <option name="PACKAGE_NAME" value="" />
+    <option name="PACKAGE_NAME" value="org.briarproject.briar.headless" />
     <option name="MAIN_CLASS_NAME" value="" />
     <option name="METHOD_NAME" value="" />
     <option name="TEST_OBJECT" value="package" />

bramble-android/build.gradle

@@ -1,3 +1,5 @@
+import com.android.build.gradle.tasks.MergeResources
+
 apply plugin: 'com.android.library'
 apply plugin: 'witness'
 apply from: 'witness.gradle'
@@ -9,8 +11,8 @@ android {
 	defaultConfig {
 		minSdkVersion 14
 		targetSdkVersion 26
-		versionCode 10103
+		versionCode 10105
-		versionName "1.1.3"
+		versionName "1.1.5"
 		consumerProguardFiles 'proguard-rules.txt'
 
 		testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
@@ -29,8 +31,9 @@ configurations {
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
 	tor 'org.briarproject:tor-android:0.3.4.8@zip'
+	tor 'org.briarproject:obfs4proxy-android:0.0.7@zip'
 
-	annotationProcessor 'com.google.dagger:dagger-compiler:2.0.2'
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
 
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 
@@ -39,13 +42,29 @@ dependencies {
 	testImplementation "org.jmock:jmock:2.8.2"
 	testImplementation "org.jmock:jmock-junit4:2.8.2"
 	testImplementation "org.jmock:jmock-legacy:2.8.2"
-	testImplementation "org.hamcrest:hamcrest-library:1.3"
-	testImplementation "org.hamcrest:hamcrest-core:1.3"
 }
 
-project.afterEvaluate {
+def torBinariesDir = 'src/main/res/raw'
-	copy {
+
-		from configurations.tor.collect { zipTree(it) }
+task cleanTorBinaries {
-		into 'src/main/res/raw'
+	doLast {
+		delete fileTree(torBinariesDir) { include '*.zip' }
 	}
 }
+
+clean.dependsOn cleanTorBinaries
+
+task unpackTorBinaries {
+	doLast {
+		copy {
+			from configurations.tor.collect { zipTree(it) }
+			into torBinariesDir
+		}
+	}
+	dependsOn cleanTorBinaries
+}
+
+tasks.withType(MergeResources) {
+	inputs.dir torBinariesDir
+	dependsOn unpackTorBinaries
+}

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

@@ -0,0 +1,11 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.battery.AndroidBatteryModule;
+import org.briarproject.bramble.network.AndroidNetworkModule;
+
+public interface BrambleAndroidEagerSingletons {
+
+	void inject(AndroidBatteryModule.EagerSingletons init);
+
+	void inject(AndroidNetworkModule.EagerSingletons init);
+}

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble;
 
+import org.briarproject.bramble.battery.AndroidBatteryModule;
 import org.briarproject.bramble.network.AndroidNetworkModule;
 import org.briarproject.bramble.plugin.tor.CircumventionModule;
 import org.briarproject.bramble.system.AndroidSystemModule;
@@ -7,10 +8,15 @@ import org.briarproject.bramble.system.AndroidSystemModule;
 import dagger.Module;
 
 @Module(includes = {
+		AndroidBatteryModule.class,
 		AndroidNetworkModule.class,
 		AndroidSystemModule.class,
 		CircumventionModule.class
 })
 public class BrambleAndroidModule {
 
+	public static void initEagerSingletons(BrambleAndroidEagerSingletons c) {
+		c.inject(new AndroidBatteryModule.EagerSingletons());
+		c.inject(new AndroidNetworkModule.EagerSingletons());
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/battery/AndroidBatteryManager.java

@@ -0,0 +1,81 @@
+package org.briarproject.bramble.battery;
+
+import android.app.Application;
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+import android.content.IntentFilter;
+
+import org.briarproject.bramble.api.battery.BatteryManager;
+import org.briarproject.bramble.api.battery.event.BatteryEvent;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.Service;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import static android.content.Intent.ACTION_BATTERY_CHANGED;
+import static android.content.Intent.ACTION_POWER_CONNECTED;
+import static android.content.Intent.ACTION_POWER_DISCONNECTED;
+import static android.os.BatteryManager.EXTRA_PLUGGED;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+
+class AndroidBatteryManager implements BatteryManager, Service {
+
+	private static final Logger LOG =
+			getLogger(AndroidBatteryManager.class.getName());
+
+	private final Context appContext;
+	private final EventBus eventBus;
+	private final AtomicBoolean used = new AtomicBoolean(false);
+
+	private volatile BroadcastReceiver batteryReceiver = null;
+
+	@Inject
+	AndroidBatteryManager(Application app, EventBus eventBus) {
+		this.appContext = app.getApplicationContext();
+		this.eventBus = eventBus;
+	}
+
+	@Override
+	public boolean isCharging() {
+		// Get the sticky intent for ACTION_BATTERY_CHANGED
+		IntentFilter filter = new IntentFilter(ACTION_BATTERY_CHANGED);
+		Intent i = appContext.registerReceiver(null, filter);
+		if (i == null) return false;
+		int status = i.getIntExtra(EXTRA_PLUGGED, 0);
+		return status != 0;
+	}
+
+	@Override
+	public void startService() {
+		if (used.getAndSet(true)) throw new IllegalStateException();
+		batteryReceiver = new BatteryReceiver();
+		IntentFilter filter = new IntentFilter();
+		filter.addAction(ACTION_POWER_CONNECTED);
+		filter.addAction(ACTION_POWER_DISCONNECTED);
+		appContext.registerReceiver(batteryReceiver, filter);
+	}
+
+	@Override
+	public void stopService() {
+		if (batteryReceiver != null)
+			appContext.unregisterReceiver(batteryReceiver);
+	}
+
+	private class BatteryReceiver extends BroadcastReceiver {
+
+		@Override
+		public void onReceive(Context ctx, Intent i) {
+			String action = i.getAction();
+			if (LOG.isLoggable(INFO)) LOG.info("Received broadcast " + action);
+			if (ACTION_POWER_CONNECTED.equals(action))
+				eventBus.broadcast(new BatteryEvent(true));
+			else if (ACTION_POWER_DISCONNECTED.equals(action))
+				eventBus.broadcast(new BatteryEvent(false));
+		}
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/battery/AndroidBatteryModule.java

@@ -0,0 +1,27 @@
+package org.briarproject.bramble.battery;
+
+import org.briarproject.bramble.api.battery.BatteryManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class AndroidBatteryModule {
+
+	public static class EagerSingletons {
+		@Inject
+		BatteryManager batteryManager;
+	}
+
+	@Provides
+	@Singleton
+	BatteryManager provideBatteryManager(LifecycleManager lifecycleManager,
+			AndroidBatteryManager batteryManager) {
+		lifecycleManager.registerService(batteryManager);
+		return batteryManager;
+	}
+}

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

@@ -3,6 +3,7 @@ package org.briarproject.bramble.network;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.network.NetworkManager;
 
+import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -11,6 +12,11 @@ import dagger.Provides;
 @Module
 public class AndroidNetworkModule {
 
+	public static class EagerSingletons {
+		@Inject
+		NetworkManager networkManager;
+	}
+
 	@Provides
 	@Singleton
 	NetworkManager provideNetworkManager(LifecycleManager lifecycleManager,

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

@@ -18,8 +18,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.util.AndroidUtils;
+import org.briarproject.bramble.util.IoUtils;
 
-import java.io.Closeable;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.ArrayList;
@@ -51,7 +51,6 @@ import static android.bluetooth.BluetoothDevice.EXTRA_DEVICE;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
@@ -161,11 +160,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	@Override
 	void tryToClose(@Nullable BluetoothServerSocket ss) {
-		try {
+		IoUtils.tryToClose(ss, LOG, WARNING);
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
 	}
 
 	@Override
@@ -195,7 +190,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 			s.connect();
 			return wrapSocket(s);
 		} catch (IOException e) {
-			tryToClose(s);
+			IoUtils.tryToClose(s, LOG, WARNING);
 			throw e;
 		}
 	}
@@ -268,14 +263,6 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		return addresses;
 	}
 
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private class BluetoothStateReceiver extends BroadcastReceiver {
 
 		@Override

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

@@ -6,6 +6,7 @@ import android.content.pm.PackageManager;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.os.PowerManager;
 
+import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
@@ -41,17 +42,18 @@ class AndroidTorPlugin extends TorPlugin {
 			Context appContext, NetworkManager networkManager,
 			LocationUtils locationUtils, SocketFactory torSocketFactory,
 			Clock clock, ResourceProvider resourceProvider,
-			CircumventionProvider circumventionProvider, Backoff backoff,
+			CircumventionProvider circumventionProvider,
+			BatteryManager batteryManager, Backoff backoff,
 			DuplexPluginCallback callback, String architecture, int maxLatency,
 			int maxIdleTime) {
 		super(ioExecutor, networkManager, locationUtils, torSocketFactory,
-				clock, resourceProvider, circumventionProvider, backoff,
+				clock, resourceProvider, circumventionProvider, batteryManager,
-				callback, architecture, maxLatency, maxIdleTime,
+				backoff, callback, architecture, maxLatency, maxIdleTime,
 				appContext.getDir("tor", MODE_PRIVATE));
 		this.appContext = appContext;
 		PowerManager pm = (PowerManager)
 				appContext.getSystemService(POWER_SERVICE);
-		assert pm != null;
+		if (pm == null) throw new AssertionError();
 		wakeLock = new RenewableWakeLock(pm, scheduler, PARTIAL_WAKE_LOCK,
 				WAKE_LOCK_TAG, 1, MINUTES);
 	}

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

@@ -3,6 +3,7 @@ package org.briarproject.bramble.plugin.tor;
 import android.content.Context;
 import android.os.Build;
 
+import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
@@ -48,6 +49,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private final BackoffFactory backoffFactory;
 	private final ResourceProvider resourceProvider;
 	private final CircumventionProvider circumventionProvider;
+	private final BatteryManager batteryManager;
 	private final Clock clock;
 
 	public AndroidTorPluginFactory(Executor ioExecutor,
@@ -55,7 +57,8 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 			NetworkManager networkManager, LocationUtils locationUtils,
 			EventBus eventBus, SocketFactory torSocketFactory,
 			BackoffFactory backoffFactory, ResourceProvider resourceProvider,
-			CircumventionProvider circumventionProvider, Clock clock) {
+			CircumventionProvider circumventionProvider,
+			BatteryManager batteryManager, Clock clock) {
 		this.ioExecutor = ioExecutor;
 		this.scheduler = scheduler;
 		this.appContext = appContext;
@@ -66,6 +69,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 		this.backoffFactory = backoffFactory;
 		this.resourceProvider = resourceProvider;
 		this.circumventionProvider = circumventionProvider;
+		this.batteryManager = batteryManager;
 		this.clock = clock;
 	}
 
@@ -104,8 +108,8 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidTorPlugin plugin = new AndroidTorPlugin(ioExecutor, scheduler,
 				appContext, networkManager, locationUtils, torSocketFactory,
-				clock, resourceProvider, circumventionProvider, backoff,
+				clock, resourceProvider, circumventionProvider, batteryManager,
-				callback, architecture, MAX_LATENCY, MAX_IDLE_TIME);
+				backoff, callback, architecture, MAX_LATENCY, MAX_IDLE_TIME);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.system;
 
+import android.annotation.SuppressLint;
 import android.app.Application;
 import android.bluetooth.BluetoothAdapter;
 import android.bluetooth.BluetoothDevice;
@@ -26,7 +27,7 @@ import static android.provider.Settings.Secure.ANDROID_ID;
 
 @Immutable
 @NotNullByDefault
-class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
+class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 
 	private static final int SEED_LENGTH = 32;
 
@@ -37,6 +38,7 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		appContext = app.getApplicationContext();
 	}
 
+	@SuppressLint("HardwareIds")
 	@Override
 	protected void writeToEntropyPool(DataOutputStream out) throws IOException {
 		super.writeToEntropyPool(out);
@@ -49,12 +51,14 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		String id = Settings.Secure.getString(contentResolver, ANDROID_ID);
 		if (id != null) out.writeUTF(id);
 		Parcel parcel = Parcel.obtain();
-		WifiManager wm =
+		WifiManager wm = (WifiManager) appContext.getApplicationContext()
-				(WifiManager) appContext.getSystemService(WIFI_SERVICE);
+				.getSystemService(WIFI_SERVICE);
-		List<WifiConfiguration> configs = wm.getConfiguredNetworks();
+		if (wm != null) {
-		if (configs != null) {
+			List<WifiConfiguration> configs = wm.getConfiguredNetworks();
-			for (WifiConfiguration config : configs)
+			if (configs != null) {
-				parcel.writeParcelable(config, 0);
+				for (WifiConfiguration config : configs)
+					parcel.writeParcelable(config, 0);
+			}
 		}
 		BluetoothAdapter bt = BluetoothAdapter.getDefaultAdapter();
 		if (bt != null) {
@@ -77,13 +81,13 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
 	private void applyOpenSslFix() {
-		byte[] seed = new LinuxSecureRandomSpi().engineGenerateSeed(
+		byte[] seed = new UnixSecureRandomSpi().engineGenerateSeed(
 				SEED_LENGTH);
 		try {
 			// Seed the OpenSSL PRNG
 			Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")
 					.getMethod("RAND_seed", byte[].class)
-					.invoke(null, seed);
+					.invoke(null, (Object) seed);
 			// Mix the output of the Linux PRNG into the OpenSSL PRNG
 			int bytesRead = (Integer) Class.forName(
 					"org.apache.harmony.xnet.provider.jsse.NativeCrypto")

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

@@ -11,15 +11,12 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
-import java.util.logging.Logger;
 
 import static android.content.Context.MODE_PRIVATE;
+import static android.os.Build.VERSION.SDK_INT;
 
 public class AndroidUtils {
 
-	private static final Logger LOG =
-			Logger.getLogger(AndroidUtils.class.getName());
-
 	// Fake Bluetooth address returned by BluetoothAdapter on API 23 and later
 	private static final String FAKE_BLUETOOTH_ADDRESS = "02:00:00:00:00:00";
 
@@ -28,7 +25,7 @@ public class AndroidUtils {
 	@SuppressWarnings("deprecation")
 	public static Collection<String> getSupportedArchitectures() {
 		List<String> abis = new ArrayList<>();
-		if (Build.VERSION.SDK_INT >= 21) {
+		if (SDK_INT >= 21) {
 			abis.addAll(Arrays.asList(Build.SUPPORTED_ABIS));
 		} else {
 			abis.add(Build.CPU_ABI);

bramble-android/witness.gradle

@@ -31,16 +31,21 @@ dependencyVerification {
         'com.android.tools:sdklib:26.2.1:sdklib-26.2.1.jar:248df7ad5eac4aeb6f96c394c76760de4b7b89ac056e54d0c21a739368b91b45',
         'com.google.code.findbugs:jsr305:1.3.9:jsr305-1.3.9.jar:905721a0eea90a81534abb7ee6ef4ea2e5e645fa1def0a5cd88402df1b46c9ed',
         'com.google.code.gson:gson:2.8.0:gson-2.8.0.jar:c6221763bd79c4f1c3dc7f750b5f29a0bb38b367b81314c4f71896e340c40825',
-        'com.google.dagger:dagger-compiler:2.0.2:dagger-compiler-2.0.2.jar:b74bc9de063dd4c6400b232231f2ef5056145b8fbecbf5382012007dd1c071b3',
+        'com.google.dagger:dagger-compiler:2.19:dagger-compiler-2.19.jar:27a4b202a2de908182edb261f8c0a264e08e5e4733d7514bc7fbf0d31da5c0fc',
-        'com.google.dagger:dagger-producers:2.0-beta:dagger-producers-2.0-beta.jar:99ec15e8a0507ba569e7655bc1165ee5e5ca5aa914b3c8f7e2c2458f724edd6b',
+        'com.google.dagger:dagger-producers:2.19:dagger-producers-2.19.jar:a17663abe0fc38b676026950907d4c5f5e2bf338375415861eaff6e3bdb0b768',
-        'com.google.dagger:dagger:2.0.2:dagger-2.0.2.jar:84c0282ed8be73a29e0475d639da030b55dee72369e58dd35ae7d4fe6243dcf9',
+        'com.google.dagger:dagger-spi:2.19:dagger-spi-2.19.jar:e7a6379d82c841f6aac2866948ad1eed716528707814602842a8d844ce04e2e1',
+        'com.google.dagger:dagger:2.19:dagger-2.19.jar:514b6f1e0727c6572e1d65cb27e4ae668b7aeaeb93a29515182965265b609939',
         'com.google.errorprone:error_prone_annotations:2.0.18:error_prone_annotations-2.0.18.jar:cb4cfad870bf563a07199f3ebea5763f0dec440fcda0b318640b1feaa788656b',
-        'com.google.guava:guava:18.0:guava-18.0.jar:d664fbfc03d2e5ce9cab2a44fb01f1d0bf9dfebeccc1a473b1f9ea31f79f6f99',
+        'com.google.errorprone:error_prone_annotations:2.1.3:error_prone_annotations-2.1.3.jar:03d0329547c13da9e17c634d1049ea2ead093925e290567e1a364fd6b1fc7ff8',
+        'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
+        'com.google.googlejavaformat:google-java-format:1.5:google-java-format-1.5.jar:aa19ad7850fb85178aa22f2fddb163b84d6ce4d0035872f30d4408195ca1144e',
         'com.google.guava:guava:23.0:guava-23.0.jar:7baa80df284117e5b945b19b98d367a85ea7b7801bd358ff657946c3bd1b6596',
+        'com.google.guava:guava:25.0-jre:guava-25.0-jre.jar:3fd4341776428c7e0e5c18a7c10de129475b69ab9d30aeafbb5c277bb6074fa9',
         'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:40ceb7157feb263949e0f503fe5f71689333a621021aa20ce0d0acee3badaa0f',
         'com.google.jimfs:jimfs:1.1:jimfs-1.1.jar:c4828e28d7c0a930af9387510b3bada7daa5c04d7c25a75c7b8b081f1c257ddd',
         'com.google.protobuf:protobuf-java:3.4.0:protobuf-java-3.4.0.jar:dce7e66b32456a1b1198da0caff3a8acb71548658391e798c79369241e6490a4',
         'com.googlecode.json-simple:json-simple:1.1:json-simple-1.1.jar:2d9484f4c649f708f47f9a479465fc729770ee65617dca3011836602264f6439',
+        'com.squareup:javapoet:1.11.1:javapoet-1.11.1.jar:9cbf2107be499ec6e95afd36b58e3ca122a24166cdd375732e51267d64058e90',
         'com.squareup:javawriter:2.5.0:javawriter-2.5.0.jar:fcfb09fb0ea0aa97d3cfe7ea792398081348e468f126b3603cb3803f240197f0',
         'com.sun.activation:javax.activation:1.2.0:javax.activation-1.2.0.jar:993302b16cd7056f21e779cc577d175a810bb4900ef73cd8fbf2b50f928ba9ce',
         'com.sun.istack:istack-commons-runtime:2.21:istack-commons-runtime-2.21.jar:c33e67a0807095f02a0e2da139412dd7c4f9cc1a4c054b3e434f96831ba950f4',
@@ -63,7 +68,9 @@ dependencyVerification {
         'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         '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:0.0.7:obfs4proxy-android-0.0.7.zip:abdfb5d889d848de9bf214f9276abbf454808a505b870819eccc9a9e985bf617',
         'org.briarproject:tor-android:0.3.4.8:tor-android-0.3.4.8.zip:989a0352d9d8d8172cd6c2137654e165e5d2beb10ed1211bab3814e224ad1926',
+        'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.codehaus.groovy:groovy-all:2.4.12:groovy-all-2.4.12.jar:6a56af4bd48903d56bec62821876cadefafd007360cc6bd0d8f7aa8d72b38be4',
         'org.codehaus.mojo:animal-sniffer-annotations:1.14:animal-sniffer-annotations-1.14.jar:2068320bd6bad744c3673ab048f67e30bef8f518996fa380033556600669905d',
         'org.glassfish.jaxb:jaxb-core:2.2.11:jaxb-core-2.2.11.jar:37bcaee8ebb04362c8352a5bf6221b86967ecdab5164c696b10b9a2bb587b2aa',

bramble-api/build.gradle

@@ -7,15 +7,13 @@ apply plugin: 'witness'
 apply from: 'witness.gradle'
 
 dependencies {
-	implementation "com.google.dagger:dagger:2.0.2"
+	implementation "com.google.dagger:dagger:2.19"
 	implementation 'com.google.code.findbugs:jsr305:3.0.2'
 
 	testImplementation 'junit:junit:4.12'
 	testImplementation "org.jmock:jmock:2.8.2"
 	testImplementation "org.jmock:jmock-junit4:2.8.2"
 	testImplementation "org.jmock:jmock-legacy:2.8.2"
-	testImplementation "org.hamcrest:hamcrest-library:1.3"
-	testImplementation "org.hamcrest:hamcrest-core:1.3"
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

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

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class Pair<A, B> {
+
+	private final A first;
+	private final B second;
+
+	public Pair(A first, B second) {
+		this.first = first;
+		this.second = second;
+	}
+
+	public A getFirst() {
+		return first;
+	}
+
+	public B getSecond() {
+		return second;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/battery/BatteryManager.java

@@ -0,0 +1,6 @@
+package org.briarproject.bramble.api.battery;
+
+public interface BatteryManager {
+
+	boolean isCharging();
+}

bramble-api/src/main/java/org/briarproject/bramble/api/battery/event/BatteryEvent.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.battery.event;
+
+import org.briarproject.bramble.api.event.Event;
+
+/**
+ * An event that is broadcast when the device starts or stops charging.
+ */
+public class BatteryEvent extends Event {
+
+	private final boolean charging;
+
+	public BatteryEvent(boolean charging) {
+		this.charging = charging;
+	}
+
+	public boolean isCharging() {
+		return charging;
+	}
+}

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

@@ -1,7 +1,6 @@
-package org.briarproject.briar.client;
+package org.briarproject.bramble.api.client;
 
 import org.briarproject.bramble.api.FormatException;
-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.MetadataParser;
@@ -12,7 +11,7 @@ import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -62,5 +61,4 @@ public abstract class BdfIncomingMessageHook implements IncomingMessageHook {
 			throw new InvalidMessageException(e);
 		}
 	}
-
 }

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

@@ -9,7 +9,7 @@ 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.sync.MessageContext;
-import org.briarproject.bramble.api.sync.ValidationManager.MessageValidator;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
 import org.briarproject.bramble.api.system.Clock;
 
 import java.util.logging.Logger;

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

@@ -13,6 +13,8 @@ import java.util.Collection;
 
 import javax.annotation.Nullable;
 
+import static org.briarproject.bramble.api.contact.PendingContact.PendingContactState.FAILED;
+
 @NotNullByDefault
 public interface ContactManager {
 
@@ -52,6 +54,35 @@ public interface ContactManager {
 			long timestamp, boolean alice, boolean verified, boolean active)
 			throws DbException;
 
+	/**
+	 * Returns the static link that needs to be sent to the contact to be added.
+	 */
+	String getRemoteContactLink();
+
+	/**
+	 * Returns true if the given link is syntactically valid.
+	 */
+	boolean isValidRemoteContactLink(String link);
+
+	/**
+	 * Requests a new contact to be added via the given {@code link}.
+	 *
+	 * @param link The link received from the contact we want to add.
+	 * @param alias The alias the user has given this contact.
+	 * @return A PendingContact representing the contact to be added.
+	 */
+	PendingContact addRemoteContactRequest(String link, String alias);
+
+	/**
+	 * Returns a list of {@link PendingContact}s.
+	 */
+	Collection<PendingContact> getPendingContacts();
+
+	/**
+	 * Removes a {@link PendingContact} that is in state {@link FAILED}.
+	 */
+	void removePendingContact(PendingContact pendingContact);
+
 	/**
 	 * Returns the contact with the given ID.
 	 */
@@ -96,6 +127,12 @@ public interface ContactManager {
 	void setContactActive(Transaction txn, ContactId c, boolean active)
 			throws DbException;
 
+	/**
+	 * Sets an alias name for the contact or unsets it if alias is null.
+	 */
+	void setContactAlias(Transaction txn, ContactId c, @Nullable String alias)
+			throws DbException;
+
 	/**
 	 * Sets an alias name for the contact or unsets it if alias is null.
 	 */

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

@@ -0,0 +1,54 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PendingContact {
+
+	public enum PendingContactState {
+		WAITING_FOR_CONNECTION,
+		CONNECTED,
+		ADDING_CONTACT,
+		FAILED
+	}
+
+	private final PendingContactId id;
+	private final String alias;
+	private final PendingContactState state;
+	private final long timestamp;
+
+	public PendingContact(PendingContactId id, String alias,
+			PendingContactState state, long timestamp) {
+		this.id = id;
+		this.alias = alias;
+		this.state = state;
+		this.timestamp = timestamp;
+	}
+
+	public String getAlias() {
+		return alias;
+	}
+
+	public PendingContactState getState() {
+		return state;
+	}
+
+	public long getTimestamp() {
+		return timestamp;
+	}
+
+	@Override
+	public int hashCode() {
+		return id.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof PendingContact &&
+				id.equals(((PendingContact) o).id);
+	}
+
+}

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

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.UniqueId;
+
+public class PendingContactId extends UniqueId {
+
+	public PendingContactId(byte[] id) {
+		super(id);
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/PendingContactStateChangedEvent.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.contact.PendingContact.PendingContactState;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a pending contact's state is changed.
+ */
+@Immutable
+@NotNullByDefault
+public class PendingContactStateChangedEvent extends Event {
+
+	private final PendingContactId id;
+	private final PendingContactState state;
+
+	public PendingContactStateChangedEvent(PendingContactId id,
+			PendingContactState state) {
+		this.id = id;
+		this.state = state;
+	}
+
+	public PendingContactId getId() {
+		return id;
+	}
+
+	public PendingContactState getPendingContactState() {
+		return state;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/data/BdfStringUtils.java

@@ -0,0 +1,71 @@
+package org.briarproject.bramble.api.data;
+
+import org.briarproject.bramble.api.Bytes;
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
+@NotNullByDefault
+public class BdfStringUtils {
+
+	public static String toString(@Nullable Object o) throws FormatException {
+		return toString(o, 0);
+	}
+
+	private static String toString(@Nullable Object o, int indent)
+			throws FormatException {
+		if (o == null || o == NULL_VALUE) return "null";
+		if (o instanceof Boolean) return o.toString();
+		if (o instanceof Number) return o.toString();
+		if (o instanceof String) return "\"" + o + "\"";
+		if (o instanceof Bytes)
+			return "x" + toHexString(((Bytes) o).getBytes());
+		if (o instanceof byte[])
+			return "x" + toHexString((byte[]) o);
+		if (o instanceof List) {
+			List<?> list = (List) o;
+			StringBuilder sb = new StringBuilder();
+			sb.append("[\n");
+			int i = 0, size = list.size();
+			for (Object e : list) {
+				indent(sb, indent + 1);
+				sb.append(toString(e, indent + 1));
+				if (i++ < size - 1) sb.append(',');
+				sb.append('\n');
+			}
+			indent(sb, indent);
+			sb.append(']');
+			return sb.toString();
+		}
+		if (o instanceof Map) {
+			Map<?, ?> map = (Map) o;
+			StringBuilder sb = new StringBuilder();
+			sb.append("{\n");
+			int i = 0, size = map.size();
+			for (Entry e : map.entrySet()) {
+				indent(sb, indent + 1);
+				sb.append(toString(e.getKey(), indent + 1));
+				sb.append(": ");
+				sb.append(toString(e.getValue(), indent + 1));
+				if (i++ < size - 1) sb.append(',');
+				sb.append('\n');
+			}
+			indent(sb, indent);
+			sb.append('}');
+			return sb.toString();
+		}
+		throw new FormatException();
+	}
+
+	private static void indent(StringBuilder sb, int indent) {
+		for (int i = 0; i < indent; i++) sb.append('\t');
+	}
+}

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

@@ -19,6 +19,7 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -28,8 +29,6 @@ import java.util.Map;
 
 import javax.annotation.Nullable;
 
-import static org.briarproject.bramble.api.sync.ValidationManager.State;
-
 /**
  * Encapsulates the database implementation and exposes high-level operations
  * to other components.
@@ -89,6 +88,14 @@ public interface DatabaseComponent {
 	<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.
+	 */
+	@Nullable
+	<R, E extends Exception> R transactionWithNullableResult(boolean readOnly,
+			NullableDbCallable<R, E> task) throws DbException, E;
+
 	/**
 	 * Stores a contact associated with the given local and remote pseudonyms,
 	 * and returns an ID for the contact.
@@ -366,12 +373,12 @@ public interface DatabaseComponent {
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
 	 * For missing dependencies and dependencies in other groups, the state
-	 * {@link State UNKNOWN} is returned.
+	 * {@link MessageState UNKNOWN} is returned.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependencies(Transaction txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependencies(Transaction txn,
-			throws DbException;
+			MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs and states of all dependents of the given message.
@@ -380,15 +387,16 @@ public interface DatabaseComponent {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependents(Transaction txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependents(Transaction txn,
-			throws DbException;
+			MessageId m) throws DbException;
 
 	/**
 	 * Gets the validation and delivery state of the given message.
 	 * <p/>
 	 * Read-only.
 	 */
-	State getMessageState(Transaction txn, MessageId m) throws DbException;
+	MessageState getMessageState(Transaction txn, MessageId m)
+			throws DbException;
 
 	/**
 	 * Returns the status of the given delivered message with respect to the
@@ -535,7 +543,7 @@ public interface DatabaseComponent {
 	/**
 	 * Sets the validation and delivery state of the given message.
 	 */
-	void setMessageState(Transaction txn, MessageId m, State state)
+	void setMessageState(Transaction txn, MessageId m, MessageState state)
 			throws DbException;
 
 	/**

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

@@ -1,5 +1,8 @@
 package org.briarproject.bramble.api.db;
 
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
 public interface DbCallable<R, E extends Exception> {
 
 	R call(Transaction txn) throws DbException, E;

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

@@ -1,5 +1,8 @@
 package org.briarproject.bramble.api.db;
 
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
 public interface DbRunnable<E extends Exception> {
 
 	void run(Transaction txn) throws DbException, E;

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

@@ -0,0 +1,12 @@
+package org.briarproject.bramble.api.db;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface NullableDbCallable<R, E extends Exception> {
+
+	@Nullable
+	R call(Transaction txn) throws DbException, E;
+}

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

@@ -10,7 +10,11 @@ import javax.annotation.concurrent.Immutable;
 public class AuthorInfo {
 
 	public enum Status {
-		NONE, ANONYMOUS, UNKNOWN, UNVERIFIED, VERIFIED, OURSELVES
+		NONE, ANONYMOUS, UNKNOWN, UNVERIFIED, VERIFIED, OURSELVES;
+
+		public boolean isContact() {
+			return this == UNVERIFIED || this == VERIFIED;
+		}
 	}
 
 	private final Status status;
@@ -35,4 +39,18 @@ public class AuthorInfo {
 		return alias;
 	}
 
+	@Override
+	public int hashCode() {
+		int hashCode = status.ordinal();
+		if (alias != null) hashCode += alias.hashCode();
+		return hashCode;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (!(o instanceof AuthorInfo)) return false;
+		AuthorInfo info = (AuthorInfo) o;
+		return status == info.status &&
+				(alias == null ? info.alias == null : alias.equals(info.alias));
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java

@@ -0,0 +1,15 @@
+package org.briarproject.bramble.api.nullsafety;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public class NullSafety {
+
+	/**
+	 * Stand-in for `Objects.requireNonNull()`.
+	 */
+	public static <T> T requireNonNull(@Nullable T t) {
+		if (t == null) throw new NullPointerException();
+		return t;
+	}
+}

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

@@ -16,6 +16,7 @@ public interface TorConstants {
 	String PREF_TOR_NETWORK = "network2";
 	String PREF_TOR_PORT = "port";
 	String PREF_TOR_MOBILE = "useMobileData";
+	String PREF_TOR_ONLY_WHEN_CHARGING = "onlyWhenCharging";
 
 	int PREF_TOR_NETWORK_AUTOMATIC = 0;
 	int PREF_TOR_NETWORK_WITHOUT_BRIDGES = 1;

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

@@ -1,87 +0,0 @@
-package org.briarproject.bramble.api.sync;
-
-import org.briarproject.bramble.api.crypto.SecretKey;
-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;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-/**
- * Responsible for managing message validators and passing them messages to
- * validate.
- */
-@NotNullByDefault
-public interface ValidationManager {
-
-	enum State {
-
-		UNKNOWN(0), INVALID(1), PENDING(2), DELIVERED(3);
-
-		private final int value;
-
-		State(int value) {
-			this.value = value;
-		}
-
-		public int getValue() {
-			return value;
-		}
-
-		public static State fromValue(int value) {
-			for (State s : values()) if (s.value == value) return s;
-			throw new IllegalArgumentException();
-		}
-	}
-
-	/**
-	 * Registers the message validator for the given client. This method
-	 * should be called before
-	 * {@link LifecycleManager#startServices(SecretKey)}.
-	 */
-	void registerMessageValidator(ClientId c, int majorVersion,
-			MessageValidator v);
-
-	/**
-	 * Registers the incoming message hook for the given client. The hook will
-	 * be called once for each incoming message that passes validation. This
-	 * method should be called before
-	 * {@link LifecycleManager#startServices(SecretKey)}.
-	 */
-	void registerIncomingMessageHook(ClientId c, int majorVersion,
-			IncomingMessageHook hook);
-
-	interface MessageValidator {
-
-		/**
-		 * Validates the given message and returns its metadata and
-		 * dependencies.
-		 */
-		MessageContext validateMessage(Message m, Group g)
-				throws InvalidMessageException;
-	}
-
-	interface IncomingMessageHook {
-
-		/**
-		 * Called once for each incoming message that passes validation.
-		 *
-		 * @return whether or not this message should be shared
-		 * @throws DbException Should only be used for real database errors.
-		 * If this is thrown, delivery will be attempted again at next startup,
-		 * whereas if an InvalidMessageException is thrown,
-		 * the message will be permanently invalidated.
-		 * @throws InvalidMessageException for any non-database error
-		 * that occurs while handling remotely created data.
-		 * This includes errors that occur while handling locally created data
-		 * in a context controlled by remotely created data
-		 * (for example, parsing the metadata of a dependency
-		 * of an incoming message).
-		 * Throwing this will delete the incoming message and its metadata
-		 * marking it as invalid in the database.
-		 * Never rethrow DbException as InvalidMessageException!
-		 */
-		boolean incomingMessage(Transaction txn, Message m, Metadata meta)
-				throws DbException, InvalidMessageException;
-	}
-}

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

@@ -3,11 +3,10 @@ package org.briarproject.bramble.api.sync.event;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 
 import javax.annotation.concurrent.Immutable;
 
-import static org.briarproject.bramble.api.sync.ValidationManager.State;
-
 /**
  * An event that is broadcast when a message state changed.
  */
@@ -17,10 +16,10 @@ public class MessageStateChangedEvent extends Event {
 
 	private final MessageId messageId;
 	private final boolean local;
-	private final State state;
+	private final MessageState state;
 
 	public MessageStateChangedEvent(MessageId messageId, boolean local,
-			State state) {
+			MessageState state) {
 		this.messageId = messageId;
 		this.local = local;
 		this.state = state;
@@ -34,7 +33,7 @@ public class MessageStateChangedEvent extends Event {
 		return local;
 	}
 
-	public State getState() {
+	public MessageState getState() {
 		return state;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/IncomingMessageHook.java

@@ -0,0 +1,31 @@
+package org.briarproject.bramble.api.sync.validation;
+
+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.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.Message;
+
+public interface IncomingMessageHook {
+
+	/**
+	 * Called once for each incoming message that passes validation.
+	 *
+	 * @return whether or not this message should be shared
+	 * @throws DbException Should only be used for real database errors.
+	 * If this is thrown, delivery will be attempted again at next startup,
+	 * whereas if an InvalidMessageException is thrown,
+	 * the message will be permanently invalidated.
+	 * @throws InvalidMessageException for any non-database error
+	 * that occurs while handling remotely created data.
+	 * This includes errors that occur while handling locally created data
+	 * in a context controlled by remotely created data
+	 * (for example, parsing the metadata of a dependency
+	 * of an incoming message).
+	 * Throwing this will delete the incoming message and its metadata
+	 * marking it as invalid in the database.
+	 * Never rethrow DbException as InvalidMessageException!
+	 */
+	boolean incomingMessage(Transaction txn, Message m, Metadata meta)
+			throws DbException, InvalidMessageException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/MessageState.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.sync.validation;
+
+public enum MessageState {
+
+	UNKNOWN(0), INVALID(1), PENDING(2), DELIVERED(3);
+
+	private final int value;
+
+	MessageState(int value) {
+		this.value = value;
+	}
+
+	public int getValue() {
+		return value;
+	}
+
+	public static MessageState fromValue(int value) {
+		for (MessageState s : values()) if (s.value == value) return s;
+		throw new IllegalArgumentException();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/MessageValidator.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.api.sync.validation;
+
+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.sync.MessageContext;
+
+public interface MessageValidator {
+
+	/**
+	 * Validates the given message and returns its metadata and
+	 * dependencies.
+	 */
+	MessageContext validateMessage(Message m, Group g)
+			throws InvalidMessageException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/ValidationManager.java

@@ -0,0 +1,31 @@
+package org.briarproject.bramble.api.sync.validation;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+
+/**
+ * Responsible for managing message validators and passing them messages to
+ * validate.
+ */
+@NotNullByDefault
+public interface ValidationManager {
+
+	/**
+	 * Registers the {@link MessageValidator} for the given client. This method
+	 * should be called before
+	 * {@link LifecycleManager#startServices(SecretKey)}.
+	 */
+	void registerMessageValidator(ClientId c, int majorVersion,
+			MessageValidator v);
+
+	/**
+	 * Registers the {@link IncomingMessageHook} for the given client. The hook
+	 * will be called once for each incoming message that passes validation.
+	 * This method should be called before
+	 * {@link LifecycleManager#startServices(SecretKey)}.
+	 */
+	void registerIncomingMessageHook(ClientId c, int majorVersion,
+			IncomingMessageHook hook);
+}

bramble-api/src/main/java/org/briarproject/bramble/api/versioning/ClientVersioningManager.java

@@ -38,6 +38,13 @@ public interface ClientVersioningManager {
 	Visibility getClientVisibility(Transaction txn, ContactId contactId,
 			ClientId clientId, int majorVersion) throws DbException;
 
+	/**
+	 * Returns the minor version of the given client that is supported by the
+	 * given contact, or -1 if the contact does not support the client.
+	 */
+	int getClientMinorVersion(Transaction txn, ContactId contactId,
+			ClientId clientId, int majorVersion) throws DbException;
+
 	interface ClientVersioningHook {
 
 		void onClientVisibilityChanging(Transaction txn, Contact c,

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

@@ -8,12 +8,15 @@ import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.net.ServerSocket;
 import java.net.Socket;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 
 import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
 public class IoUtils {
@@ -54,16 +57,35 @@ public class IoUtils {
 			out.flush();
 			out.close();
 		} catch (IOException e) {
-			tryToClose(in);
+			tryToClose(in, LOG, WARNING);
-			tryToClose(out);
+			tryToClose(out, LOG, WARNING);
 		}
 	}
 
-	private static void tryToClose(@Nullable Closeable c) {
+	public static void tryToClose(@Nullable Closeable c, Logger logger,
+			Level level) {
 		try {
 			if (c != null) c.close();
 		} catch (IOException e) {
-			// We did our best
+			logException(logger, level, e);
+		}
+	}
+
+	public static void tryToClose(@Nullable Socket s, Logger logger,
+			Level level) {
+		try {
+			if (s != null) s.close();
+		} catch (IOException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	public static void tryToClose(@Nullable ServerSocket ss, Logger logger,
+			Level level) {
+		try {
+			if (ss != null) ss.close();
+		} catch (IOException e) {
+			logException(logger, level, e);
 		}
 	}
 

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

@@ -10,8 +10,6 @@ public class OsUtils {
 	@Nullable
 	private static final String os = System.getProperty("os.name");
 	@Nullable
-	private static final String version = System.getProperty("os.version");
-	@Nullable
 	private static final String vendor = System.getProperty("java.vendor");
 
 	public static boolean isWindows() {

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

@@ -47,7 +47,7 @@ public class StringUtils {
 		try {
 			return s.getBytes("UTF-8");
 		} catch (UnsupportedEncodingException e) {
-			throw new RuntimeException(e);
+			throw new AssertionError(e);
 		}
 	}
 
@@ -63,7 +63,7 @@ public class StringUtils {
 		try {
 			return decoder.decode(buffer).toString();
 		} catch (CharacterCodingException e) {
-			throw new RuntimeException(e);
+			throw new AssertionError(e);
 		}
 	}
 

bramble-api/src/test/java/org/briarproject/bramble/api/identity/AuthorInfoTest.java

@@ -0,0 +1,42 @@
+package org.briarproject.bramble.api.identity;
+
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.junit.Test;
+
+import static org.briarproject.bramble.api.identity.AuthorInfo.Status.NONE;
+import static org.briarproject.bramble.api.identity.AuthorInfo.Status.VERIFIED;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+public class AuthorInfoTest extends BrambleTestCase {
+
+	@Test
+	public void testEquals() {
+		assertEquals(
+				new AuthorInfo(NONE),
+				new AuthorInfo(NONE, null)
+		);
+		assertEquals(
+				new AuthorInfo(NONE, "test"),
+				new AuthorInfo(NONE, "test")
+		);
+
+		assertNotEquals(
+				new AuthorInfo(NONE),
+				new AuthorInfo(VERIFIED)
+		);
+		assertNotEquals(
+				new AuthorInfo(NONE, "test"),
+				new AuthorInfo(NONE)
+		);
+		assertNotEquals(
+				new AuthorInfo(NONE),
+				new AuthorInfo(NONE, "test")
+		);
+		assertNotEquals(
+				new AuthorInfo(NONE, "a"),
+				new AuthorInfo(NONE, "b")
+		);
+	}
+
+}

bramble-api/witness.gradle

@@ -2,7 +2,7 @@ dependencyVerification {
     verify = [
         'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
-        'com.google.dagger:dagger:2.0.2:dagger-2.0.2.jar:84c0282ed8be73a29e0475d639da030b55dee72369e58dd35ae7d4fe6243dcf9',
+        'com.google.dagger:dagger:2.19:dagger-2.19.jar:514b6f1e0727c6572e1d65cb27e4ae668b7aeaeb93a29515182965265b609939',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
         'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',

bramble-core/build.gradle

@@ -3,10 +3,10 @@ sourceCompatibility = 1.8
 targetCompatibility = 1.8
 
 apply plugin: 'ru.vyarus.animalsniffer'
-apply plugin: 'net.ltgt.apt'
 apply plugin: 'idea'
 apply plugin: 'witness'
 apply from: 'witness.gradle'
+apply from: '../dagger.gradle'
 
 dependencies {
 	implementation project(path: ':bramble-api', configuration: 'default')
@@ -17,7 +17,7 @@ dependencies {
 	implementation 'org.whispersystems:curve25519-java:0.5.0'
 	implementation 'org.briarproject:jtorctl:0.3'
 
-	apt 'com.google.dagger:dagger-compiler:2.0.2'
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation 'org.hsqldb:hsqldb:2.3.5' // The last version that supports Java 1.6
@@ -25,10 +25,8 @@ dependencies {
 	testImplementation "org.jmock:jmock:2.8.2"
 	testImplementation "org.jmock:jmock-junit4:2.8.2"
 	testImplementation "org.jmock:jmock-legacy:2.8.2"
-	testImplementation "org.hamcrest:hamcrest-library:1.3"
-	testImplementation "org.hamcrest:hamcrest-core:1.3"
 
-	testApt 'com.google.dagger:dagger-compiler:2.0.2'
+	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.19'
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

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

@@ -8,7 +8,7 @@ import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.reporting.ReportingModule;
-import org.briarproject.bramble.sync.SyncModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
@@ -31,11 +31,11 @@ public interface BrambleCoreEagerSingletons {
 
 	void inject(ReportingModule.EagerSingletons init);
 
-	void inject(SyncModule.EagerSingletons init);
-
 	void inject(SystemModule.EagerSingletons init);
 
 	void inject(TransportModule.EagerSingletons init);
 
+	void inject(ValidationModule.EagerSingletons init);
+
 	void inject(VersioningModule.EagerSingletons init);
 }

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

@@ -19,6 +19,7 @@ import org.briarproject.bramble.reporting.ReportingModule;
 import org.briarproject.bramble.settings.SettingsModule;
 import org.briarproject.bramble.socks.SocksModule;
 import org.briarproject.bramble.sync.SyncModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
@@ -47,6 +48,7 @@ import dagger.Module;
 		SyncModule.class,
 		SystemModule.class,
 		TransportModule.class,
+		ValidationModule.class,
 		VersioningModule.class
 })
 public class BrambleCoreModule {
@@ -60,9 +62,9 @@ public class BrambleCoreModule {
 		c.inject(new PluginModule.EagerSingletons());
 		c.inject(new PropertiesModule.EagerSingletons());
 		c.inject(new ReportingModule.EagerSingletons());
-		c.inject(new SyncModule.EagerSingletons());
 		c.inject(new SystemModule.EagerSingletons());
 		c.inject(new TransportModule.EagerSingletons());
+		c.inject(new ValidationModule.EagerSingletons());
 		c.inject(new VersioningModule.EagerSingletons());
 	}
 }

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

@@ -0,0 +1,67 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.GuardedBy;
+
+@NotNullByDefault
+public class PriorityExecutor {
+
+	private final Object lock = new Object();
+	private final Executor delegate, high, low;
+	@GuardedBy("lock")
+	private final Queue<Runnable> highQueue = new LinkedList<>();
+	@GuardedBy("lock")
+	private final Queue<Runnable> lowQueue = new LinkedList<>();
+
+	@GuardedBy("lock")
+	private boolean isTaskRunning = false;
+
+	public PriorityExecutor(Executor delegate) {
+		this.delegate = delegate;
+		high = r -> submit(r, true);
+		low = r -> submit(r, false);
+	}
+
+	public Executor getHighPriorityExecutor() {
+		return high;
+	}
+
+	public Executor getLowPriorityExecutor() {
+		return low;
+	}
+
+	private void submit(Runnable r, boolean isHighPriority) {
+		Runnable wrapped = () -> {
+			try {
+				r.run();
+			} finally {
+				scheduleNext();
+			}
+		};
+		synchronized (lock) {
+			if (!isTaskRunning && highQueue.isEmpty() &&
+					(isHighPriority || lowQueue.isEmpty())) {
+				isTaskRunning = true;
+				delegate.execute(wrapped);
+			} else if (isHighPriority) {
+				highQueue.add(wrapped);
+			} else {
+				lowQueue.add(wrapped);
+			}
+		}
+	}
+
+	private void scheduleNext() {
+		synchronized (lock) {
+			Runnable next = highQueue.poll();
+			if (next == null) next = lowQueue.poll();
+			if (next == null) isTaskRunning = false;
+			else delegate.execute(next);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/battery/DefaultBatteryManagerModule.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.battery;
+
+import org.briarproject.bramble.api.battery.BatteryManager;
+
+import dagger.Module;
+import dagger.Provides;
+
+/**
+ * Provides a default implementation of {@link BatteryManager} for systems
+ * without batteries.
+ */
+@Module
+public class DefaultBatteryManagerModule {
+
+	@Provides
+	BatteryManager provideBatteryManager() {
+		return () -> false;
+	}
+}

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

@@ -82,13 +82,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void addLocalMessage(Message m, BdfDictionary metadata,
 			boolean shared) throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> addLocalMessage(txn, m, metadata, shared));
-		try {
-			addLocalMessage(txn, m, metadata, shared);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override
@@ -113,15 +107,7 @@ class ClientHelperImpl implements ClientHelper {
 
 	@Override
 	public Message getMessage(MessageId m) throws DbException {
-		Message message;
+		return db.transactionWithResult(true, txn -> getMessage(txn, m));
-		Transaction txn = db.startTransaction(true);
-		try {
-			message = getMessage(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return message;
 	}
 
 	@Override
@@ -132,15 +118,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfList getMessageAsList(MessageId m) throws DbException,
 			FormatException {
-		BdfList list;
+		return db.transactionWithResult(true, txn -> getMessageAsList(txn, m));
-		Transaction txn = db.startTransaction(true);
-		try {
-			list = getMessageAsList(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return list;
 	}
 
 	@Override
@@ -152,15 +130,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfDictionary getGroupMetadataAsDictionary(GroupId g)
 			throws DbException, FormatException {
-		BdfDictionary dictionary;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				getGroupMetadataAsDictionary(txn, g));
-		try {
-			dictionary = getGroupMetadataAsDictionary(txn, g);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return dictionary;
 	}
 
 	@Override
@@ -173,15 +144,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfDictionary getMessageMetadataAsDictionary(MessageId m)
 			throws DbException, FormatException {
-		BdfDictionary dictionary;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				getMessageMetadataAsDictionary(txn, m));
-		try {
-			dictionary = getMessageMetadataAsDictionary(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return dictionary;
 	}
 
 	@Override
@@ -194,15 +158,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public Map<MessageId, BdfDictionary> getMessageMetadataAsDictionary(
 			GroupId g) throws DbException, FormatException {
-		Map<MessageId, BdfDictionary> map;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				getMessageMetadataAsDictionary(txn, g));
-		try {
-			map = getMessageMetadataAsDictionary(txn, g);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return map;
 	}
 
 	@Override
@@ -219,15 +176,8 @@ class ClientHelperImpl implements ClientHelper {
 	public Map<MessageId, BdfDictionary> getMessageMetadataAsDictionary(
 			GroupId g, BdfDictionary query) throws DbException,
 			FormatException {
-		Map<MessageId, BdfDictionary> map;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				getMessageMetadataAsDictionary(txn, g, query));
-		try {
-			map = getMessageMetadataAsDictionary(txn, g, query);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return map;
 	}
 
 	@Override
@@ -245,13 +195,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void mergeGroupMetadata(GroupId g, BdfDictionary metadata)
 			throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> mergeGroupMetadata(txn, g, metadata));
-		try {
-			mergeGroupMetadata(txn, g, metadata);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override
@@ -263,13 +207,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void mergeMessageMetadata(MessageId m, BdfDictionary metadata)
 			throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> mergeMessageMetadata(txn, m, metadata));
-		try {
-			mergeMessageMetadata(txn, m, metadata);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeTaskImpl.java

@@ -13,7 +13,6 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
@@ -158,7 +157,8 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 				streamWriterFactory.createContactExchangeStreamWriter(out,
 						alice ? aliceHeaderKey : bobHeaderKey);
 		RecordWriter recordWriter =
-				recordWriterFactory.createRecordWriter(streamWriter.getOutputStream());
+				recordWriterFactory
+						.createRecordWriter(streamWriter.getOutputStream());
 
 		// Derive the nonces to be signed
 		byte[] aliceNonce = crypto.mac(ALICE_NONCE_LABEL, masterSecret,
@@ -287,19 +287,14 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private ContactId addContact(Author remoteAuthor, long timestamp,
 			Map<TransportId, TransportProperties> remoteProperties)
 			throws DbException {
-		ContactId contactId;
+		return db.transactionWithResult(false, txn -> {
-		Transaction txn = db.startTransaction(false);
+			ContactId contactId = contactManager.addContact(txn, remoteAuthor,
-		try {
-			contactId = contactManager.addContact(txn, remoteAuthor,
 					localAuthor.getId(), masterSecret, timestamp, alice,
 					true, true);
 			transportPropertyManager.addRemoteProperties(txn, contactId,
 					remoteProperties);
-			db.commitTransaction(txn);
+			return contactId;
-		} finally {
+		});
-			db.endTransaction(txn);
-		}
-		return contactId;
 	}
 
 	private void tryToClose(DuplexTransportConnection conn) {

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -3,6 +3,8 @@ package org.briarproject.bramble.contact;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
@@ -19,12 +21,16 @@ import org.briarproject.bramble.api.transport.KeyManager;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Random;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.regex.Pattern;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.contact.PendingContact.PendingContactState.WAITING_FOR_CONNECTION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.OURSELVES;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.UNKNOWN;
@@ -36,6 +42,12 @@ import static org.briarproject.bramble.util.StringUtils.toUtf8;
 @NotNullByDefault
 class ContactManagerImpl implements ContactManager {
 
+	private static final int LINK_LENGTH = 64;
+	private static final String REMOTE_CONTACT_LINK =
+			"briar://" + getRandomBase32String(LINK_LENGTH);
+	private static final Pattern LINK_REGEX =
+			Pattern.compile("(briar://)?([a-z2-7]{" + LINK_LENGTH + "})");
+
 	private final DatabaseComponent db;
 	private final KeyManager keyManager;
 	private final IdentityManager identityManager;
@@ -79,42 +91,63 @@ class ContactManagerImpl implements ContactManager {
 	public ContactId addContact(Author remote, AuthorId local, SecretKey master,
 			long timestamp, boolean alice, boolean verified, boolean active)
 			throws DbException {
-		ContactId c;
+		return db.transactionWithResult(false, txn ->
-		Transaction txn = db.startTransaction(false);
+				addContact(txn, remote, local, master, timestamp, alice,
-		try {
+						verified, active));
-			c = addContact(txn, remote, local, master, timestamp, alice,
+	}
-					verified, active);
+
-			db.commitTransaction(txn);
+	@Override
-		} finally {
+	public String getRemoteContactLink() {
-			db.endTransaction(txn);
+		// TODO replace with real implementation
+		return REMOTE_CONTACT_LINK;
+	}
+
+	@SuppressWarnings("SameParameterValue")
+	private static String getRandomBase32String(int length) {
+		Random random = new Random();
+		char[] c = new char[length];
+		for (int i = 0; i < length; i++) {
+			int character = random.nextInt(32);
+			if (character < 26) c[i] = (char) ('a' + character);
+			else c[i] = (char) ('2' + (character - 26));
 		}
-		return c;
+		return new String(c);
+	}
+
+	@Override
+	public boolean isValidRemoteContactLink(String link) {
+		return LINK_REGEX.matcher(link).matches();
+	}
+
+	@Override
+	public PendingContact addRemoteContactRequest(String link, String alias) {
+		// TODO replace with real implementation
+		PendingContactId id = new PendingContactId(link.getBytes());
+		return new PendingContact(id, alias, WAITING_FOR_CONNECTION,
+				System.currentTimeMillis());
+	}
+
+	@Override
+	public Collection<PendingContact> getPendingContacts() {
+		// TODO replace with real implementation
+		return emptyList();
+	}
+
+	@Override
+	public void removePendingContact(PendingContact pendingContact) {
+		// TODO replace with real implementation
 	}
 
 	@Override
 	public Contact getContact(ContactId c) throws DbException {
-		Contact contact;
+		return db.transactionWithResult(true, txn -> db.getContact(txn, c));
-		Transaction txn = db.startTransaction(true);
-		try {
-			contact = db.getContact(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return contact;
 	}
 
 	@Override
 	public Contact getContact(AuthorId remoteAuthorId, AuthorId localAuthorId)
 			throws DbException {
-		Transaction txn = db.startTransaction(true);
+		return db.transactionWithResult(true, txn ->
-		try {
+				getContact(txn, remoteAuthorId, localAuthorId));
-			Contact c = getContact(txn, remoteAuthorId, localAuthorId);
-			db.commitTransaction(txn);
-			return c;
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override
@@ -132,14 +165,8 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public Collection<Contact> getActiveContacts() throws DbException {
-		Collection<Contact> contacts;
+		Collection<Contact> contacts =
-		Transaction txn = db.startTransaction(true);
+				db.transactionWithResult(true, db::getContacts);
-		try {
-			contacts = db.getContacts(txn);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 		List<Contact> active = new ArrayList<>(contacts.size());
 		for (Contact c : contacts) if (c.isActive()) active.add(c);
 		return active;
@@ -147,13 +174,7 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public void removeContact(ContactId c) throws DbException {
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> removeContact(txn, c));
-		try {
-			removeContact(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override
@@ -163,14 +184,20 @@ class ContactManagerImpl implements ContactManager {
 	}
 
 	@Override
-	public void setContactAlias(ContactId c, @Nullable String alias)
+	public void setContactAlias(Transaction txn, ContactId c,
-			throws DbException {
+			@Nullable String alias) throws DbException {
 		if (alias != null) {
 			int aliasLength = toUtf8(alias).length;
 			if (aliasLength == 0 || aliasLength > MAX_AUTHOR_NAME_LENGTH)
 				throw new IllegalArgumentException();
 		}
-		db.transaction(false, txn -> db.setContactAlias(txn, c, alias));
+		db.setContactAlias(txn, c, alias);
+	}
+
+	@Override
+	public void setContactAlias(ContactId c, @Nullable String alias)
+			throws DbException {
+		db.transaction(false, txn -> setContactAlias(txn, c, alias));
 	}
 
 	@Override
@@ -182,15 +209,8 @@ class ContactManagerImpl implements ContactManager {
 	@Override
 	public boolean contactExists(AuthorId remoteAuthorId,
 			AuthorId localAuthorId) throws DbException {
-		boolean exists;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				contactExists(txn, remoteAuthorId, localAuthorId));
-		try {
-			exists = contactExists(txn, remoteAuthorId, localAuthorId);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return exists;
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/data/BdfReaderImpl.java

@@ -29,6 +29,7 @@ import static org.briarproject.bramble.data.Types.STRING_16;
 import static org.briarproject.bramble.data.Types.STRING_32;
 import static org.briarproject.bramble.data.Types.STRING_8;
 import static org.briarproject.bramble.data.Types.TRUE;
+import static org.briarproject.bramble.util.StringUtils.fromUtf8;
 
 @NotThreadSafe
 @NotNullByDefault
@@ -253,7 +254,7 @@ class BdfReaderImpl implements BdfReader {
 		if (length < 0 || length > maxBufferSize) throw new FormatException();
 		if (length == 0) return "";
 		readIntoBuffer(length);
-		return new String(buf, 0, length, "UTF-8");
+		return fromUtf8(buf, 0, length);
 	}
 
 	private int readStringLength() throws IOException {

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

@@ -22,7 +22,7 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -106,7 +106,7 @@ interface Database<T> {
 	 * @param sender the contact from whom the message was received, or null
 	 * if the message was created locally.
 	 */
-	void addMessage(T txn, Message m, State state, boolean shared,
+	void addMessage(T txn, Message m, MessageState state, boolean shared,
 			@Nullable ContactId sender) throws DbException;
 
 	/**
@@ -114,7 +114,7 @@ interface Database<T> {
 	 * in the given state.
 	 */
 	void addMessageDependency(T txn, Message dependent, MessageId dependency,
-			State dependentState) throws DbException;
+			MessageState dependentState) throws DbException;
 
 	/**
 	 * Records that a message has been offered by the given contact.
@@ -310,11 +310,11 @@ interface Database<T> {
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
 	 * For missing dependencies and dependencies in other groups, the state
-	 * {@link State UNKNOWN} is returned.
+	 * {@link MessageState UNKNOWN} is returned.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependencies(T txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependencies(T txn, MessageId m)
 			throws DbException;
 
 	/**
@@ -324,7 +324,7 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependents(T txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependents(T txn, MessageId m)
 			throws DbException;
 
 	/**
@@ -383,7 +383,7 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	State getMessageState(T txn, MessageId m) throws DbException;
+	MessageState getMessageState(T txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the status of all delivered messages in the given group with
@@ -637,7 +637,8 @@ interface Database<T> {
 	/**
 	 * Sets the validation and delivery state of the given message.
 	 */
-	void setMessageState(T txn, MessageId m, State state) throws DbException;
+	void setMessageState(T txn, MessageId m, MessageState state)
+			throws DbException;
 
 	/**
 	 * Sets the reordering window for the given key set and transport in the

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

@@ -19,6 +19,7 @@ import org.briarproject.bramble.api.db.NoSuchGroupException;
 import org.briarproject.bramble.api.db.NoSuchLocalAuthorException;
 import org.briarproject.bramble.api.db.NoSuchMessageException;
 import org.briarproject.bramble.api.db.NoSuchTransportException;
+import org.briarproject.bramble.api.db.NullableDbCallable;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
@@ -42,7 +43,6 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
 import org.briarproject.bramble.api.sync.event.GroupAddedEvent;
 import org.briarproject.bramble.api.sync.event.GroupRemovedEvent;
 import org.briarproject.bramble.api.sync.event.GroupVisibilityUpdatedEvent;
@@ -54,6 +54,7 @@ import org.briarproject.bramble.api.sync.event.MessageToAckEvent;
 import org.briarproject.bramble.api.sync.event.MessageToRequestEvent;
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -74,8 +75,8 @@ import javax.inject.Inject;
 import static java.util.logging.Level.WARNING;
 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.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_OFFERED_MESSAGES;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -193,6 +194,20 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		}
 	}
 
+	@Override
+	public <R, E extends Exception> R transactionWithNullableResult(
+			boolean readOnly, NullableDbCallable<R, E> task)
+			throws DbException, E {
+		Transaction txn = startTransaction(readOnly);
+		try {
+			R result = task.call(txn);
+			commitTransaction(txn);
+			return result;
+		} finally {
+			endTransaction(txn);
+		}
+	}
+
 	private T unbox(Transaction transaction) {
 		if (transaction.isCommitted()) throw new IllegalStateException();
 		return txnClass.cast(transaction.unbox());
@@ -564,7 +579,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public State getMessageState(Transaction transaction, MessageId m)
+	public MessageState getMessageState(Transaction transaction, MessageId m)
 			throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
@@ -604,8 +619,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependencies(Transaction transaction,
+	public Map<MessageId, MessageState> getMessageDependencies(
-			MessageId m) throws DbException {
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -613,8 +628,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependents(Transaction transaction,
+	public Map<MessageId, MessageState> getMessageDependents(
-			MessageId m) throws DbException {
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -861,7 +876,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public void setContactAlias(Transaction transaction, ContactId c,
-			String alias) throws DbException {
+			@Nullable String alias) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
@@ -903,7 +918,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public void setMessageState(Transaction transaction, MessageId m,
-			State state) throws DbException {
+			MessageState state) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
@@ -920,10 +935,10 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, dependent.getId()))
 			throw new NoSuchMessageException();
-		State dependentState = db.getMessageState(txn, dependent.getId());
+		MessageState dependentState =
+				db.getMessageState(txn, dependent.getId());
 		for (MessageId dependency : dependencies) {
-			db.addMessageDependency(txn, dependent, dependency,
+			db.addMessageDependency(txn, dependent, dependency, dependentState);
-					dependentState);
 		}
 	}
 

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

@@ -3,7 +3,7 @@ package org.briarproject.bramble.db;
 class DatabaseTypes {
 
 	private final String hashType, secretType, binaryType;
-    private final String counterType, stringType;
+	private final String counterType, stringType;
 
 	public DatabaseTypes(String hashType, String secretType, String binaryType,
 			String counterType, String stringType) {
@@ -17,11 +17,11 @@ class DatabaseTypes {
 	/**
 	 * Replaces database type placeholders in a statement with the actual types.
 	 * These placeholders are currently supported:
-	 *	<li> _HASH
+	 * <li> _HASH
-	 *	<li> _SECRET
+	 * <li> _SECRET
-	 *	<li> _BINARY
+	 * <li> _BINARY
-	 *	<li> _COUNTER
+	 * <li> _COUNTER
-	 *	<li> _STRING
+	 * <li> _STRING
 	 */
 	String replaceTypes(String s) {
 		s = s.replaceAll("_HASH", hashType);

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

@@ -15,16 +15,23 @@ import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;
+import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
 /**
  * Contains all the H2-specific code for the database.
  */
 @NotNullByDefault
 class H2Database extends JdbcDatabase {
 
+	private static final Logger LOG = getLogger(H2Database.class.getName());
+
 	private static final String HASH_TYPE = "BINARY(32)";
 	private static final String SECRET_TYPE = "BINARY(32)";
 	private static final String BINARY_TYPE = "BINARY";
@@ -121,8 +128,8 @@ class H2Database extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
-			tryToClose(c);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -14,16 +14,24 @@ import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;
+import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
 /**
  * Contains all the HSQLDB-specific code for the database.
  */
 @NotNullByDefault
 class HyperSqlDatabase extends JdbcDatabase {
 
+	private static final Logger LOG =
+			getLogger(HyperSqlDatabase.class.getName());
+
 	private static final String HASH_TYPE = "BINARY(32)";
 	private static final String SECRET_TYPE = "BINARY(32)";
 	private static final String BINARY_TYPE = "BINARY";
@@ -72,8 +80,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
-			tryToClose(c);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -122,8 +130,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
-			tryToClose(c);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -24,7 +24,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.KeySet;
@@ -64,14 +64,15 @@ import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
+import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+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.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;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
@@ -458,30 +459,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
 	}
 
-	private void tryToClose(@Nullable ResultSet rs) {
-		try {
-			if (rs != null) rs.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	protected void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	protected void tryToClose(@Nullable Connection c) {
-		try {
-			if (c != null) c.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private void createTables(Connection txn) throws DbException {
 		Statement s = null;
 		try {
@@ -502,7 +479,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_INCOMING_KEYS));
 			s.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -519,7 +496,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(INDEX_STATUSES_BY_CONTACT_ID_TIMESTAMP);
 			s.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -566,11 +543,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		} catch (SQLException e) {
 			// Try to close the connection
 			logException(LOG, WARNING, e);
-			try {
+			tryToClose(txn, LOG, WARNING);
-				txn.close();
-			} catch (SQLException e1) {
-				logException(LOG, WARNING, e1);
-			}
 			// Whatever happens, allow the database to close
 			connectionsLock.lock();
 			try {
@@ -659,8 +632,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return c;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -681,7 +654,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -704,7 +677,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			// Create a status row for each message in the group
 			addStatus(txn, c, g, groupShared);
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -724,7 +697,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			while (rs.next()) {
 				MessageId id = new MessageId(rs.getBytes(1));
 				long timestamp = rs.getLong(2);
-				State state = State.fromValue(rs.getInt(3));
+				MessageState state = MessageState.fromValue(rs.getInt(3));
 				boolean messageShared = rs.getBoolean(4);
 				int length = rs.getInt(5);
 				boolean deleted = rs.getBoolean(6);
@@ -735,8 +708,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs.close();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -761,13 +734,13 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public void addMessage(Connection txn, Message m, State state,
+	public void addMessage(Connection txn, Message m, MessageState state,
 			boolean messageShared, @Nullable ContactId sender)
 			throws DbException {
 		PreparedStatement ps = null;
@@ -810,7 +783,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -840,14 +813,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	private void addStatus(Connection txn, MessageId m, ContactId c, GroupId g,
-			long timestamp, int length, State state, boolean groupShared,
+			long timestamp, int length, MessageState state, boolean groupShared,
 			boolean messageShared, boolean deleted, boolean seen)
 			throws DbException {
 		PreparedStatement ps = null;
@@ -873,14 +846,15 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
 	public void addMessageDependency(Connection txn, Message dependent,
-			MessageId dependency, State dependentState) throws DbException {
+			MessageId dependency, MessageState dependentState)
+			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -891,9 +865,9 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setBytes(1, dependency.getBytes());
 			ps.setBytes(2, dependent.getGroupId().getBytes());
 			rs = ps.executeQuery();
-			State dependencyState = null;
+			MessageState dependencyState = null;
 			if (rs.next()) {
-				dependencyState = State.fromValue(rs.getInt(1));
+				dependencyState = MessageState.fromValue(rs.getInt(1));
 				if (rs.next()) throw new DbStateException();
 			}
 			rs.close();
@@ -914,8 +888,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -934,7 +908,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1014,8 +988,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return keySetId;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1038,8 +1012,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1060,8 +1034,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1082,8 +1056,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1104,8 +1078,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1126,8 +1100,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1148,8 +1122,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1173,8 +1147,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1197,8 +1171,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return count;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1222,7 +1196,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1239,7 +1213,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1272,8 +1246,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			return new Contact(c, author, localAuthorId, alias, verified,
 					active);
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1309,8 +1283,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return contacts;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1332,8 +1306,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1370,8 +1344,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return contacts;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1394,8 +1368,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return new Group(g, clientId, majorVersion, descriptor);
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1422,8 +1396,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return groups;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1448,8 +1422,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return v;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1472,8 +1446,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return visible;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1504,8 +1478,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return localAuthor;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1536,8 +1510,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return authors;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1565,8 +1539,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
 			return new Message(m, g, timestamp, body);
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1589,8 +1563,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1627,8 +1601,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (intersection == null) throw new AssertionError();
 			return intersection;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1660,8 +1634,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return all;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1695,8 +1669,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1719,8 +1693,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1745,8 +1719,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1775,8 +1749,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return statuses;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1806,14 +1780,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return status;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependencies(Connection txn,
+	public Map<MessageId, MessageState> getMessageDependencies(Connection txn,
 			MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1824,10 +1798,10 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
-			Map<MessageId, State> dependencies = new HashMap<>();
+			Map<MessageId, MessageState> dependencies = new HashMap<>();
 			while (rs.next()) {
 				MessageId dependency = new MessageId(rs.getBytes(1));
-				State state = State.fromValue(rs.getInt(2));
+				MessageState state = MessageState.fromValue(rs.getInt(2));
 				if (rs.wasNull())
 					state = UNKNOWN; // Missing or in a different group
 				dependencies.put(dependency, state);
@@ -1836,14 +1810,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return dependencies;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependents(Connection txn,
+	public Map<MessageId, MessageState> getMessageDependents(Connection txn,
 			MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1857,24 +1831,24 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
-			Map<MessageId, State> dependents = new HashMap<>();
+			Map<MessageId, MessageState> dependents = new HashMap<>();
 			while (rs.next()) {
 				MessageId dependent = new MessageId(rs.getBytes(1));
-				State state = State.fromValue(rs.getInt(2));
+				MessageState state = MessageState.fromValue(rs.getInt(2));
 				dependents.put(dependent, state);
 			}
 			rs.close();
 			ps.close();
 			return dependents;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public State getMessageState(Connection txn, MessageId m)
+	public MessageState getMessageState(Connection txn, MessageId m)
 			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1884,14 +1858,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
 			if (!rs.next()) throw new DbStateException();
-			State state = State.fromValue(rs.getInt(1));
+			MessageState state = MessageState.fromValue(rs.getInt(1));
 			if (rs.next()) throw new DbStateException();
 			rs.close();
 			ps.close();
 			return state;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1915,8 +1889,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1949,8 +1923,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1974,8 +1948,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2013,8 +1987,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2032,7 +2006,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	private Collection<MessageId> getMessagesInState(Connection txn,
-			State state) throws DbException {
+			MessageState state) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2047,8 +2021,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2075,8 +2049,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2105,8 +2079,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return nextSendTime;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2144,8 +2118,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2167,8 +2141,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return s;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2233,8 +2207,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return keys;
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2253,7 +2227,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2280,7 +2254,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2307,7 +2281,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2337,7 +2311,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2359,7 +2333,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs = ps.executeQuery();
 			if (!rs.next()) throw new DbStateException();
 			GroupId g = new GroupId(rs.getBytes(1));
-			State state = State.fromValue(rs.getInt(2));
+			MessageState state = MessageState.fromValue(rs.getInt(2));
 			rs.close();
 			ps.close();
 			// Insert any keys that don't already exist
@@ -2382,8 +2356,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2449,7 +2423,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			return added;
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2496,7 +2470,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2515,7 +2489,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2534,7 +2508,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2553,7 +2527,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2570,7 +2544,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2586,7 +2560,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2614,7 +2588,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2631,7 +2605,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2647,7 +2621,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2666,7 +2640,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return affected == 1;
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2691,7 +2665,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2708,7 +2682,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2729,7 +2703,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2748,7 +2722,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2766,7 +2740,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2784,7 +2758,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2803,7 +2777,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2833,7 +2807,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2859,13 +2833,13 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public void setMessageState(Connection txn, MessageId m, State state)
+	public void setMessageState(Connection txn, MessageId m, MessageState state)
 			throws DbException {
 		PreparedStatement ps = null;
 		try {
@@ -2912,7 +2886,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2935,7 +2909,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2954,7 +2928,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2990,8 +2964,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
+			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -3058,7 +3032,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows < 0 || rows > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -0,0 +1,42 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class JdbcUtils {
+
+	static void tryToClose(@Nullable ResultSet rs, Logger logger, Level level) {
+		try {
+			if (rs != null) rs.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	static void tryToClose(@Nullable Statement s, Logger logger, Level level) {
+		try {
+			if (s != null) s.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	static void tryToClose(@Nullable Connection c, Logger logger, Level level) {
+		try {
+			if (c != null) c.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+}

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

@@ -7,10 +7,8 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration38_39 implements Migration<Connection> {
 
@@ -40,16 +38,8 @@ class Migration38_39 implements Migration<Connection> {
 					+ " ALTER COLUMN contactId"
 					+ " SET NOT NULL");
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

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

@@ -7,10 +7,8 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration39_40 implements Migration<Connection> {
 
@@ -39,16 +37,8 @@ class Migration39_40 implements Migration<Connection> {
 					+ " ALTER COLUMN eta"
 					+ " SET NOT NULL");
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

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

@@ -7,11 +7,9 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration40_41 implements Migration<Connection> {
 
@@ -39,18 +37,10 @@ class Migration40_41 implements Migration<Connection> {
 		try {
 			s = txn.createStatement();
 			s.execute("ALTER TABLE contacts"
-					+ dbTypes.replaceTypes(" ADD alias VARCHAR"));
+					+ dbTypes.replaceTypes(" ADD alias _STRING"));
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

bramble-core/src/main/java/org/briarproject/bramble/identity/IdentityManagerImpl.java

@@ -67,27 +67,16 @@ class IdentityManagerImpl implements IdentityManager {
 			LOG.info("No local author to store");
 			return;
 		}
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> db.addLocalAuthor(txn, cached));
-		try {
+		LOG.info("Local author stored");
-			db.addLocalAuthor(txn, cached);
-			db.commitTransaction(txn);
-			LOG.info("Local author stored");
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 
 	@Override
 	public LocalAuthor getLocalAuthor() throws DbException {
 		if (cachedAuthor == null) {
-			Transaction txn = db.startTransaction(true);
+			cachedAuthor =
-			try {
+					db.transactionWithResult(true, this::loadLocalAuthor);
-				cachedAuthor = loadLocalAuthor(txn);
+			LOG.info("Local author loaded");
-				LOG.info("Local author loaded");
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
 		}
 		LocalAuthor cached = cachedAuthor;
 		if (cached == null) throw new AssertionError();

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

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MigrationListener;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
@@ -115,20 +114,16 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 			dbLatch.countDown();
 			eventBus.broadcast(new LifecycleEvent(STARTING_SERVICES));
 
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				for (Client c : clients) {
-					start = now();
+					long start1 = now();
 					c.createLocalState(txn);
 					if (LOG.isLoggable(FINE)) {
 						logDuration(LOG, "Starting client "
-								+ c.getClass().getSimpleName(), start);
+								+ c.getClass().getSimpleName(), start1);
 					}
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 			for (Service s : services) {
 				start = now();
 				s.startService();

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

@@ -4,12 +4,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 
 import java.io.File;
-import java.io.IOException;
 import java.io.InputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportReader implements TransportConnectionReader {
@@ -34,11 +33,7 @@ class FileTransportReader implements TransportConnectionReader {
 
 	@Override
 	public void dispose(boolean exception, boolean recognised) {
-		try {
+		tryToClose(in, LOG, WARNING);
-			in.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
 		plugin.readerFinished(file, exception, recognised);
 	}
 }

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

@@ -4,12 +4,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
 
 import java.io.File;
-import java.io.IOException;
 import java.io.OutputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportWriter implements TransportConnectionWriter {
@@ -44,11 +43,7 @@ class FileTransportWriter implements TransportConnectionWriter {
 
 	@Override
 	public void dispose(boolean exception) {
-		try {
+		tryToClose(out, LOG, WARNING);
-			out.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
 		plugin.writerFinished(file, exception);
 	}
 }

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

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
@@ -35,7 +36,6 @@ import static org.briarproject.bramble.api.plugin.LanTcpConstants.ID;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PREF_LAN_IP_PORTS;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PROP_IP_PORTS;
 import static org.briarproject.bramble.util.ByteUtils.MAX_16_BIT_UNSIGNED;
-import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubSocketAddress;
 
 @NotNullByDefault
@@ -293,11 +293,7 @@ class LanTcpPlugin extends TcpPlugin {
 
 		@Override
 		public void close() {
-			try {
+			IoUtils.tryToClose(ss, LOG, WARNING);
-				ss.close();
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-			}
 		}
 	}
 

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

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
@@ -153,13 +154,8 @@ abstract class TcpPlugin implements DuplexPlugin {
 	}
 
 	protected void tryToClose(@Nullable ServerSocket ss) {
-		try {
+		IoUtils.tryToClose(ss, LOG, WARNING);
-			if (ss != null) ss.close();
+		callback.transportDisabled();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
 	}
 
 	String getIpPortString(InetSocketAddress a) {

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

@@ -4,6 +4,8 @@ import net.freehaven.tor.control.EventHandler;
 import net.freehaven.tor.control.TorControlConnection;
 
 import org.briarproject.bramble.PoliteExecutor;
+import org.briarproject.bramble.api.battery.BatteryManager;
+import org.briarproject.bramble.api.battery.event.BatteryEvent;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.event.Event;
@@ -29,7 +31,6 @@ import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 import org.briarproject.bramble.util.IoUtils;
 
-import java.io.Closeable;
 import java.io.EOFException;
 import java.io.File;
 import java.io.FileInputStream;
@@ -68,6 +69,7 @@ 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;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V2;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V3;
@@ -96,13 +98,14 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private final LocationUtils locationUtils;
 	private final SocketFactory torSocketFactory;
 	private final Clock clock;
+	private final BatteryManager batteryManager;
 	private final Backoff backoff;
 	private final DuplexPluginCallback callback;
 	private final String architecture;
 	private final CircumventionProvider circumventionProvider;
 	private final ResourceProvider resourceProvider;
 	private final int maxLatency, maxIdleTime, socketTimeout;
-	private final File torDirectory, torFile, geoIpFile, configFile;
+	private final File torDirectory, torFile, geoIpFile, obfs4File, configFile;
 	private final File doneFile, cookieFile;
 	private final ConnectionStatus connectionStatus;
 	private final AtomicBoolean used = new AtomicBoolean(false);
@@ -121,7 +124,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	TorPlugin(Executor ioExecutor, NetworkManager networkManager,
 			LocationUtils locationUtils, SocketFactory torSocketFactory,
 			Clock clock, ResourceProvider resourceProvider,
-			CircumventionProvider circumventionProvider, Backoff backoff,
+			CircumventionProvider circumventionProvider,
+			BatteryManager batteryManager, Backoff backoff,
 			DuplexPluginCallback callback, String architecture, int maxLatency,
 			int maxIdleTime, File torDirectory) {
 		this.ioExecutor = ioExecutor;
@@ -131,6 +135,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		this.clock = clock;
 		this.resourceProvider = resourceProvider;
 		this.circumventionProvider = circumventionProvider;
+		this.batteryManager = batteryManager;
 		this.backoff = backoff;
 		this.callback = callback;
 		this.architecture = architecture;
@@ -142,6 +147,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		this.torDirectory = torDirectory;
 		torFile = new File(torDirectory, "tor");
 		geoIpFile = new File(torDirectory, "geoip");
+		obfs4File = new File(torDirectory, "obfs4proxy");
 		configFile = new File(torDirectory, "torrc");
 		doneFile = new File(torDirectory, "done");
 		cookieFile = new File(torDirectory, ".tor/control_auth_cookie");
@@ -260,7 +266,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			throw new PluginException(e);
 		}
 		// Check whether we're online
-		updateConnectionStatus(networkManager.getNetworkStatus());
+		updateConnectionStatus(networkManager.getNetworkStatus(),
+				batteryManager.isCharging());
 		// Bind a server socket to receive incoming hidden service connections
 		bind();
 	}
@@ -284,14 +291,20 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			in = getGeoIpInputStream();
 			out = new FileOutputStream(geoIpFile);
 			IoUtils.copyAndClose(in, out);
+			// Unzip the Obfs4 proxy to the filesystem
+			in = getObfs4InputStream();
+			out = new FileOutputStream(obfs4File);
+			IoUtils.copyAndClose(in, out);
+			// Make the Obfs4 proxy executable
+			if (!obfs4File.setExecutable(true, true)) throw new IOException();
 			// Copy the config file to the filesystem
 			in = getConfigInputStream();
 			out = new FileOutputStream(configFile);
 			IoUtils.copyAndClose(in, out);
 			doneFile.createNewFile();
 		} catch (IOException e) {
-			tryToClose(in);
+			IoUtils.tryToClose(in, LOG, WARNING);
-			tryToClose(out);
+			IoUtils.tryToClose(out, LOG, WARNING);
 			throw new PluginException(e);
 		}
 	}
@@ -314,26 +327,20 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		return zin;
 	}
 
+	private InputStream getObfs4InputStream() throws IOException {
+		if (LOG.isLoggable(INFO))
+			LOG.info("Installing obfs4proxy binary for " + architecture);
+		InputStream in = resourceProvider
+				.getResourceInputStream("obfs4proxy_" + architecture, ".zip");
+		ZipInputStream zin = new ZipInputStream(in);
+		if (zin.getNextEntry() == null) throw new IOException();
+		return zin;
+	}
+
 	private InputStream getConfigInputStream() {
 		return getClass().getClassLoader().getResourceAsStream("torrc");
 	}
 
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void tryToClose(@Nullable Socket s) {
-		try {
-			if (s != null) s.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private void listFiles(File f) {
 		if (f.isDirectory()) {
 			File[] children = f.listFiles();
@@ -355,7 +362,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			}
 			return b;
 		} finally {
-			tryToClose(in);
+			IoUtils.tryToClose(in, LOG, WARNING);
 		}
 	}
 
@@ -395,13 +402,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void tryToClose(@Nullable ServerSocket ss) {
-		try {
+		IoUtils.tryToClose(ss, LOG, WARNING);
-			if (ss != null) ss.close();
+		callback.transportDisabled();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
 	}
 
 	private void publishHiddenService(String port) {
@@ -472,6 +474,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		if (enable) {
 			Collection<String> conf = new ArrayList<>();
 			conf.add("UseBridges 1");
+			conf.add("ClientTransportPlugin obfs4 exec " +
+					obfs4File.getAbsolutePath());
 			conf.addAll(circumventionProvider.getBridges());
 			controlConnection.setConf(conf);
 		} else {
@@ -568,7 +572,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				LOG.info("Could not connect to " + scrubOnion(bestOnion)
 						+ ": " + e.toString());
 			}
-			tryToClose(s);
+			IoUtils.tryToClose(s, LOG, WARNING);
 			return null;
 		}
 	}
@@ -609,7 +613,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			LOG.info("OR connection " + status + " " + orName);
 		if (status.equals("CLOSED") || status.equals("FAILED")) {
 			// Check whether we've lost connectivity
-			updateConnectionStatus(networkManager.getNetworkStatus());
+			updateConnectionStatus(networkManager.getNetworkStatus(),
+					batteryManager.isCharging());
 		}
 	}
 
@@ -644,13 +649,20 @@ 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. Could be
+				// Works around a bug introduced in Tor 0.3.4.8.
-				// replaced with callback.transportDisabled() when fixed.
+				// https://trac.torproject.org/projects/tor/ticket/28027
+				// Could be replaced with callback.transportDisabled()
+				// when fixed.
 				disableNetwork();
-				updateConnectionStatus(networkManager.getNetworkStatus());
+				updateConnectionStatus(networkManager.getNetworkStatus(),
+						batteryManager.isCharging());
 			}
 		} else if (e instanceof NetworkStatusEvent) {
-			updateConnectionStatus(((NetworkStatusEvent) e).getStatus());
+			updateConnectionStatus(((NetworkStatusEvent) e).getStatus(),
+					batteryManager.isCharging());
+		} else if (e instanceof BatteryEvent) {
+			updateConnectionStatus(networkManager.getNetworkStatus(),
+					((BatteryEvent) e).isCharging());
 		}
 	}
 
@@ -664,7 +676,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		});
 	}
 
-	private void updateConnectionStatus(NetworkStatus status) {
+	private void updateConnectionStatus(NetworkStatus status,
+			boolean charging) {
 		connectionStatusExecutor.execute(() -> {
 			if (!running) return;
 			boolean online = status.isConnected();
@@ -675,6 +688,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			int network = settings.getInt(PREF_TOR_NETWORK,
 					PREF_TOR_NETWORK_AUTOMATIC);
 			boolean useMobile = settings.getBoolean(PREF_TOR_MOBILE, true);
+			boolean onlyWhenCharging =
+					settings.getBoolean(PREF_TOR_ONLY_WHEN_CHARGING, false);
 			boolean bridgesWork = circumventionProvider.doBridgesWork(country);
 			boolean automatic = network == PREF_TOR_NETWORK_AUTOMATIC;
 
@@ -682,15 +697,19 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				LOG.info("Online: " + online + ", wifi: " + wifi);
 				if ("".equals(country)) LOG.info("Country code unknown");
 				else LOG.info("Country code: " + country);
+				LOG.info("Charging: " + charging);
 			}
 
 			try {
 				if (!online) {
 					LOG.info("Disabling network, device is offline");
 					enableNetwork(false);
+				} else if (!charging && onlyWhenCharging) {
+					LOG.info("Disabling network, device is on battery");
+					enableNetwork(false);
 				} else if (network == PREF_TOR_NETWORK_NEVER ||
 						(!useMobile && !wifi)) {
-					LOG.info("Disabling network due to setting");
+					LOG.info("Disabling network, device is using mobile data");
 					enableNetwork(false);
 				} else if (automatic && blocked && !bridgesWork) {
 					LOG.info("Disabling network, country is blocked");
@@ -705,12 +724,24 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 					enableBridges(false);
 					enableNetwork(true);
 				}
+				if (online && wifi && charging) {
+					LOG.info("Enabling connection padding");
+					enableConnectionPadding(true);
+				} else {
+					LOG.info("Disabling connection padding");
+					enableConnectionPadding(false);
+				}
 			} catch (IOException e) {
 				logException(LOG, WARNING, e);
 			}
 		});
 	}
 
+	private void enableConnectionPadding(boolean enable) throws IOException {
+		if (!running) return;
+		controlConnection.setConf("ConnectionPadding", enable ? "1" : "0");
+	}
+
 	// TODO remove when sufficient time has passed. Added 2018-08-15
 	private void migrateSettings() {
 		Settings sOld = callback.getSettings();

bramble-core/src/main/java/org/briarproject/bramble/properties/PropertiesModule.java

@@ -5,7 +5,7 @@ import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.data.MetadataEncoder;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
-import org.briarproject.bramble.api.sync.ValidationManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 

bramble-core/src/main/java/org/briarproject/bramble/properties/TransportPropertyManagerImpl.java

@@ -24,7 +24,7 @@ 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.ValidationManager.IncomingMessageHook;
+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;
@@ -142,15 +142,7 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public Map<TransportId, TransportProperties> getLocalProperties()
 			throws DbException {
-		Map<TransportId, TransportProperties> local;
+		return db.transactionWithResult(true, this::getLocalProperties);
-		Transaction txn = db.startTransaction(true);
-		try {
-			local = getLocalProperties(txn);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return local;
 	}
 
 	@Override
@@ -176,9 +168,8 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	public TransportProperties getLocalProperties(TransportId t)
 			throws DbException {
 		try {
-			TransportProperties p = null;
+			return db.transactionWithResult(true, txn -> {
-			Transaction txn = db.startTransaction(true);
+				TransportProperties p = null;
-			try {
 				// Find the latest local update
 				LatestUpdate latest = findLatest(txn, localGroup.getId(), t,
 						true);
@@ -188,11 +179,8 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 							latest.messageId);
 					p = parseProperties(message);
 				}
-				db.commitTransaction(txn);
+				return p == null ? new TransportProperties() : p;
-			} finally {
+			});
-				db.endTransaction(txn);
-			}
-			return p == null ? new TransportProperties() : p;
 		} catch (FormatException e) {
 			throw new DbException(e);
 		}
@@ -201,16 +189,12 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public Map<ContactId, TransportProperties> getRemoteProperties(
 			TransportId t) throws DbException {
-		Map<ContactId, TransportProperties> remote = new HashMap<>();
+		return db.transactionWithResult(true, txn -> {
-		Transaction txn = db.startTransaction(true);
+			Map<ContactId, TransportProperties> remote = new HashMap<>();
-		try {
 			for (Contact c : db.getContacts(txn))
 				remote.put(c.getId(), getRemoteProperties(txn, c, t));
-			db.commitTransaction(txn);
+			return remote;
-		} finally {
+		});
-			db.endTransaction(txn);
-		}
-		return remote;
 	}
 
 	private TransportProperties getRemoteProperties(Transaction txn, Contact c,
@@ -234,23 +218,15 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public TransportProperties getRemoteProperties(ContactId c, TransportId t)
 			throws DbException {
-		TransportProperties p;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				getRemoteProperties(txn, db.getContact(txn, c), t));
-		try {
-			p = getRemoteProperties(txn, db.getContact(txn, c), t);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return p;
 	}
 
 	@Override
 	public void mergeLocalProperties(TransportId t, TransportProperties p)
 			throws DbException {
 		try {
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				// Merge the new properties with any existing properties
 				TransportProperties merged;
 				boolean changed;
@@ -287,10 +263,7 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 							db.removeMessage(txn, latest.messageId);
 					}
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 		} catch (FormatException e) {
 			throw new DbException(e);
 		}

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

@@ -12,7 +12,6 @@ import org.briarproject.bramble.api.reporting.DevReporter;
 import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
-import java.io.Closeable;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
@@ -26,13 +25,12 @@ import java.net.Socket;
 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 java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @Immutable
 @NotNullByDefault
@@ -66,7 +64,7 @@ class DevReporterImpl implements DevReporter, EventListener {
 			s.setSoTimeout(SOCKET_TIMEOUT);
 			return s;
 		} catch (IOException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw e;
 		}
 	}
@@ -88,8 +86,7 @@ class DevReporterImpl implements DevReporter, EventListener {
 			writer.append(armoured);
 			writer.flush();
 		} finally {
-			if (writer != null)
+			tryToClose(writer, LOG, WARNING);
-				writer.close();
 		}
 	}
 
@@ -121,27 +118,11 @@ class DevReporterImpl implements DevReporter, EventListener {
 				f.delete();
 			} catch (IOException e) {
 				LOG.log(WARNING, "Failed to send reports", e);
-				tryToClose(out);
+				tryToClose(out, LOG, WARNING);
-				tryToClose(in);
+				tryToClose(in, LOG, WARNING);
 				return;
 			}
 		}
 		LOG.info("Reports sent");
 	}
-
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void tryToClose(@Nullable Socket s) {
-		try {
-			if (s != null) s.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

bramble-core/src/main/java/org/briarproject/bramble/settings/SettingsManagerImpl.java

@@ -23,15 +23,8 @@ class SettingsManagerImpl implements SettingsManager {
 
 	@Override
 	public Settings getSettings(String namespace) throws DbException {
-		Settings s;
+		return db.transactionWithResult(true, txn ->
-		Transaction txn = db.startTransaction(true);
+				db.getSettings(txn, namespace));
-		try {
-			s = db.getSettings(txn, namespace);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return s;
 	}
 
 	@Override
@@ -42,12 +35,6 @@ class SettingsManagerImpl implements SettingsManager {
 
 	@Override
 	public void mergeSettings(Settings s, String namespace) throws DbException {
-		Transaction txn = db.startTransaction(false);
+		db.transaction(false, txn -> db.mergeSettings(txn, s, namespace));
-		try {
-			db.mergeSettings(txn, s, namespace);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
 	}
 }

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

@@ -5,7 +5,6 @@ import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -230,14 +229,8 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (interrupted) return;
 			if (!generateAckQueued.getAndSet(false)) throw new AssertionError();
 			try {
-				Ack a;
+				Ack a = db.transactionWithNullableResult(false, txn ->
-				Transaction txn = db.startTransaction(false);
+						db.generateAck(txn, contactId, MAX_MESSAGE_IDS));
-				try {
-					a = db.generateAck(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated ack: " + (a != null));
 				if (a != null) writerTasks.add(new WriteAck(a));
@@ -275,16 +268,15 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateBatchQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Collection<Message> b;
+				Collection<Message> b =
-				Transaction txn = db.startTransaction(false);
+						db.transactionWithNullableResult(false, txn -> {
-				try {
+							Collection<Message> batch =
-					b = db.generateRequestedBatch(txn, contactId,
+									db.generateRequestedBatch(txn, contactId,
-							MAX_RECORD_PAYLOAD_BYTES, maxLatency);
+											MAX_RECORD_PAYLOAD_BYTES,
-					setNextSendTime(db.getNextSendTime(txn, contactId));
+											maxLatency);
-					db.commitTransaction(txn);
+							setNextSendTime(db.getNextSendTime(txn, contactId));
-				} finally {
+							return batch;
-					db.endTransaction(txn);
+						});
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated batch: " + (b != null));
 				if (b != null) writerTasks.add(new WriteBatch(b));
@@ -322,16 +314,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateOfferQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Offer o;
+				Offer o = db.transactionWithNullableResult(false, txn -> {
-				Transaction txn = db.startTransaction(false);
+					Offer offer = db.generateOffer(txn, contactId,
-				try {
+							MAX_MESSAGE_IDS, maxLatency);
-					o = db.generateOffer(txn, contactId, MAX_MESSAGE_IDS,
-							maxLatency);
 					setNextSendTime(db.getNextSendTime(txn, contactId));
-					db.commitTransaction(txn);
+					return offer;
-				} finally {
+				});
-					db.endTransaction(txn);
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated offer: " + (o != null));
 				if (o != null) writerTasks.add(new WriteOffer(o));
@@ -369,14 +357,8 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateRequestQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Request r;
+				Request r = db.transactionWithNullableResult(false, txn ->
-				Transaction txn = db.startTransaction(false);
+						db.generateRequest(txn, contactId, MAX_MESSAGE_IDS));
-				try {
-					r = db.generateRequest(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated request: " + (r != null));
 				if (r != null) writerTasks.add(new WriteRequest(r));

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

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -120,13 +119,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
+				db.transaction(false, txn ->
-				try {
+						db.receiveAck(txn, contactId, ack));
-					db.receiveAck(txn, contactId, ack);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -146,13 +140,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
+				db.transaction(false, txn ->
-				try {
+						db.receiveMessage(txn, contactId, message));
-					db.receiveMessage(txn, contactId, message);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -172,13 +161,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
+				db.transaction(false, txn ->
-				try {
+						db.receiveOffer(txn, contactId, offer));
-					db.receiveOffer(txn, contactId, offer);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -198,13 +182,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
+				db.transaction(false, txn ->
-				try {
+						db.receiveRequest(txn, contactId, request));
-					db.receiveRequest(txn, contactId, request);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();

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

@@ -5,7 +5,6 @@ import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -47,7 +46,8 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private static final Logger LOG =
 			Logger.getLogger(SimplexOutgoingSession.class.getName());
 
-	private static final ThrowingRunnable<IOException> CLOSE = () -> {};
+	private static final ThrowingRunnable<IOException> CLOSE = () -> {
+	};
 
 	private final DatabaseComponent db;
 	private final Executor dbExecutor;
@@ -128,14 +128,8 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		public void run() {
 			if (interrupted) return;
 			try {
-				Ack a;
+				Ack a = db.transactionWithNullableResult(false, txn ->
-				Transaction txn = db.startTransaction(false);
+						db.generateAck(txn, contactId, MAX_MESSAGE_IDS));
-				try {
-					a = db.generateAck(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated ack: " + (a != null));
 				if (a == null) decrementOutstandingQueries();
@@ -172,15 +166,10 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		public void run() {
 			if (interrupted) return;
 			try {
-				Collection<Message> b;
+				Collection<Message> b =
-				Transaction txn = db.startTransaction(false);
+						db.transactionWithNullableResult(false, txn ->
-				try {
+								db.generateBatch(txn, contactId,
-					b = db.generateBatch(txn, contactId,
+										MAX_RECORD_PAYLOAD_BYTES, maxLatency));
-							MAX_RECORD_PAYLOAD_BYTES, maxLatency);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 				if (LOG.isLoggable(INFO))
 					LOG.info("Generated batch: " + (b != null));
 				if (b == null) decrementOutstandingQueries();

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

@@ -1,23 +1,11 @@
 package org.briarproject.bramble.sync;
 
-import org.briarproject.bramble.PoliteExecutor;
-import org.briarproject.bramble.api.crypto.CryptoComponent;
-import org.briarproject.bramble.api.crypto.CryptoExecutor;
-import org.briarproject.bramble.api.db.DatabaseComponent;
-import org.briarproject.bramble.api.db.DatabaseExecutor;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.sync.GroupFactory;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.SyncRecordReaderFactory;
 import org.briarproject.bramble.api.sync.SyncRecordWriterFactory;
 import org.briarproject.bramble.api.sync.SyncSessionFactory;
-import org.briarproject.bramble.api.sync.ValidationManager;
-import org.briarproject.bramble.api.system.Clock;
 
-import java.util.concurrent.Executor;
-
-import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -26,29 +14,14 @@ import dagger.Provides;
 @Module
 public class SyncModule {
 
-	public static class EagerSingletons {
-		@Inject
-		ValidationManager validationManager;
-	}
-
-	/**
-	 * The maximum number of validation tasks to delegate to the crypto
-	 * executor concurrently.
-	 * <p>
-	 * The number of available processors can change during the lifetime of the
-	 * JVM, so this is just a reasonable guess.
-	 */
-	private static final int MAX_CONCURRENT_VALIDATION_TASKS =
-			Math.max(1, Runtime.getRuntime().availableProcessors() - 1);
-
 	@Provides
-	GroupFactory provideGroupFactory(CryptoComponent crypto) {
+	GroupFactory provideGroupFactory(GroupFactoryImpl groupFactory) {
-		return new GroupFactoryImpl(crypto);
+		return groupFactory;
 	}
 
 	@Provides
-	MessageFactory provideMessageFactory(CryptoComponent crypto) {
+	MessageFactory provideMessageFactory(MessageFactoryImpl messageFactory) {
-		return new MessageFactoryImpl(crypto);
+		return messageFactory;
 	}
 
 	@Provides
@@ -65,30 +38,8 @@ public class SyncModule {
 
 	@Provides
 	@Singleton
-	SyncSessionFactory provideSyncSessionFactory(DatabaseComponent db,
+	SyncSessionFactory provideSyncSessionFactory(
-			@DatabaseExecutor Executor dbExecutor, EventBus eventBus,
+			SyncSessionFactoryImpl syncSessionFactory) {
-			Clock clock, SyncRecordReaderFactory recordReaderFactory,
+		return syncSessionFactory;
-			SyncRecordWriterFactory recordWriterFactory) {
-		return new SyncSessionFactoryImpl(db, dbExecutor, eventBus, clock,
-				recordReaderFactory, recordWriterFactory);
-	}
-
-	@Provides
-	@Singleton
-	ValidationManager provideValidationManager(
-			LifecycleManager lifecycleManager, EventBus eventBus,
-			ValidationManagerImpl validationManager) {
-		lifecycleManager.registerService(validationManager);
-		eventBus.addListener(validationManager);
-		return validationManager;
-	}
-
-	@Provides
-	@Singleton
-	@ValidationExecutor
-	Executor provideValidationExecutor(
-			@CryptoExecutor Executor cryptoExecutor) {
-		return new PoliteExecutor("ValidationExecutor", cryptoExecutor,
-				MAX_CONCURRENT_VALIDATION_TASKS);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/sync/validation/ValidationExecutor.java

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;

bramble-core/src/main/java/org/briarproject/bramble/sync/validation/ValidationManagerImpl.java

@@ -1,5 +1,6 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
@@ -17,8 +18,11 @@ import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager;
 import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.MessageState;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.versioning.ClientMajorVersion;
 
 import java.util.Collection;
@@ -36,9 +40,9 @@ import javax.inject.Inject;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
+import static org.briarproject.bramble.api.sync.validation.MessageState.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
+import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @ThreadSafe
@@ -97,14 +101,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void validateOutstandingMessages() {
 		try {
-			Queue<MessageId> unvalidated = new LinkedList<>();
+			Queue<MessageId> unvalidated = new LinkedList<>(
-			Transaction txn = db.startTransaction(true);
+					db.transactionWithResult(true, db::getMessagesToValidate));
-			try {
-				unvalidated.addAll(db.getMessagesToValidate(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
 			validateNextMessageAsync(unvalidated);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -119,18 +117,14 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void validateNextMessage(Queue<MessageId> unvalidated) {
 		try {
-			Message m;
+			Pair<Message, Group> mg = db.transactionWithResult(true, txn -> {
-			Group g;
-			Transaction txn = db.startTransaction(true);
-			try {
 				MessageId id = unvalidated.poll();
-				m = db.getMessage(txn, id);
+				if (id == null) throw new AssertionError();
-				g = db.getGroup(txn, m.getGroupId());
+				Message m = db.getMessage(txn, id);
-				db.commitTransaction(txn);
+				Group g = db.getGroup(txn, m.getGroupId());
-			} finally {
+				return new Pair<>(m, g);
-				db.endTransaction(txn);
+			});
-			}
+			validateMessageAsync(mg.getFirst(), mg.getSecond());
-			validateMessageAsync(m, g);
 			validateNextMessageAsync(unvalidated);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before validation");
@@ -150,14 +144,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void deliverOutstandingMessages() {
 		try {
-			Queue<MessageId> pending = new LinkedList<>();
+			Queue<MessageId> pending = new LinkedList<>(
-			Transaction txn = db.startTransaction(true);
+					db.transactionWithResult(true, db::getPendingMessages));
-			try {
-				pending.addAll(db.getPendingMessages(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
 			deliverNextPendingMessageAsync(pending);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -172,24 +160,24 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void deliverNextPendingMessage(Queue<MessageId> pending) {
 		try {
-			boolean anyInvalid = false, allDelivered = true;
+			Queue<MessageId> toShare = new LinkedList<>();
-			Queue<MessageId> toShare = null;
+			Queue<MessageId> invalidate = new LinkedList<>();
-			Queue<MessageId> invalidate = null;
+			db.transaction(false, txn -> {
-			Transaction txn = db.startTransaction(false);
+				boolean anyInvalid = false, allDelivered = true;
-			try {
 				MessageId id = pending.poll();
+				if (id == null) throw new AssertionError();
 				// Check if message is still pending
 				if (db.getMessageState(txn, id) == PENDING) {
 					// Check if dependencies are valid and delivered
-					Map<MessageId, State> states =
+					Map<MessageId, MessageState> states =
 							db.getMessageDependencies(txn, id);
-					for (Entry<MessageId, State> e : states.entrySet()) {
+					for (Entry<MessageId, MessageState> e : states.entrySet()) {
 						if (e.getValue() == INVALID) anyInvalid = true;
 						if (e.getValue() != DELIVERED) allDelivered = false;
 					}
 					if (anyInvalid) {
 						invalidateMessage(txn, id);
-						invalidate = getDependentsToInvalidate(txn, id);
+						addDependentsToInvalidate(txn, id, invalidate);
 					} else if (allDelivered) {
 						Message m = db.getMessage(txn, id);
 						Group g = db.getGroup(txn, m.getGroupId());
@@ -200,22 +188,19 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						DeliveryResult result =
 								deliverMessage(txn, m, c, majorVersion, meta);
 						if (result.valid) {
-							pending.addAll(getPendingDependents(txn, id));
+							addPendingDependents(txn, id, pending);
 							if (result.share) {
 								db.setMessageShared(txn, id);
-								toShare = new LinkedList<>(states.keySet());
+								toShare.addAll(states.keySet());
 							}
 						} else {
-							invalidate = getDependentsToInvalidate(txn, id);
+							addDependentsToInvalidate(txn, id, invalidate);
 						}
 					}
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
+			if (!invalidate.isEmpty()) invalidateNextMessageAsync(invalidate);
-				db.endTransaction(txn);
+			if (!toShare.isEmpty()) shareNextMessageAsync(toShare);
-			}
-			if (invalidate != null) invalidateNextMessageAsync(invalidate);
-			if (toShare != null) shareNextMessageAsync(toShare);
 			deliverNextPendingMessageAsync(pending);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before delivery");
@@ -264,20 +249,19 @@ class ValidationManagerImpl implements ValidationManager, Service,
 			MessageContext context) {
 		try {
 			MessageId id = m.getId();
-			boolean anyInvalid = false, allDelivered = true;
+			Queue<MessageId> invalidate = new LinkedList<>();
-			Queue<MessageId> invalidate = null;
+			Queue<MessageId> pending = new LinkedList<>();
-			Queue<MessageId> pending = null;
+			Queue<MessageId> toShare = new LinkedList<>();
-			Queue<MessageId> toShare = null;
+			db.transaction(false, txn -> {
-			Transaction txn = db.startTransaction(false);
+				boolean anyInvalid = false, allDelivered = true;
-			try {
 				// Check if message has any dependencies
 				Collection<MessageId> dependencies = context.getDependencies();
 				if (!dependencies.isEmpty()) {
 					db.addMessageDependencies(txn, m, dependencies);
 					// Check if dependencies are valid and delivered
-					Map<MessageId, State> states =
+					Map<MessageId, MessageState> states =
 							db.getMessageDependencies(txn, id);
-					for (Entry<MessageId, State> e : states.entrySet()) {
+					for (Entry<MessageId, MessageState> e : states.entrySet()) {
 						if (e.getValue() == INVALID) anyInvalid = true;
 						if (e.getValue() != DELIVERED) allDelivered = false;
 					}
@@ -285,7 +269,7 @@ class ValidationManagerImpl implements ValidationManager, Service,
 				if (anyInvalid) {
 					if (db.getMessageState(txn, id) != INVALID) {
 						invalidateMessage(txn, id);
-						invalidate = getDependentsToInvalidate(txn, id);
+						addDependentsToInvalidate(txn, id, invalidate);
 					}
 				} else {
 					Metadata meta = context.getMetadata();
@@ -294,25 +278,22 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						DeliveryResult result =
 								deliverMessage(txn, m, c, majorVersion, meta);
 						if (result.valid) {
-							pending = getPendingDependents(txn, id);
+							addPendingDependents(txn, id, pending);
 							if (result.share) {
 								db.setMessageShared(txn, id);
-								toShare = new LinkedList<>(dependencies);
+								toShare.addAll(dependencies);
 							}
 						} else {
-							invalidate = getDependentsToInvalidate(txn, id);
+							addDependentsToInvalidate(txn, id, invalidate);
 						}
 					} else {
 						db.setMessageState(txn, id, PENDING);
 					}
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
+			if (!invalidate.isEmpty()) invalidateNextMessageAsync(invalidate);
-				db.endTransaction(txn);
+			if (!pending.isEmpty()) deliverNextPendingMessageAsync(pending);
-			}
+			if (!toShare.isEmpty()) shareNextMessageAsync(toShare);
-			if (invalidate != null) invalidateNextMessageAsync(invalidate);
-			if (pending != null) deliverNextPendingMessageAsync(pending);
-			if (toShare != null) shareNextMessageAsync(toShare);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed during validation");
 		} catch (NoSuchGroupException e) {
@@ -342,14 +323,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	}
 
 	@DatabaseExecutor
-	private Queue<MessageId> getPendingDependents(Transaction txn, MessageId m)
+	private void addPendingDependents(Transaction txn, MessageId m,
-			throws DbException {
+			Queue<MessageId> pending) throws DbException {
-		Queue<MessageId> pending = new LinkedList<>();
+		Map<MessageId, MessageState> states = db.getMessageDependents(txn, m);
-		Map<MessageId, State> states = db.getMessageDependents(txn, m);
+		for (Entry<MessageId, MessageState> e : states.entrySet()) {
-		for (Entry<MessageId, State> e : states.entrySet()) {
 			if (e.getValue() == PENDING) pending.add(e.getKey());
 		}
-		return pending;
 	}
 
 	private void shareOutstandingMessagesAsync() {
@@ -359,14 +338,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void shareOutstandingMessages() {
 		try {
-			Queue<MessageId> toShare = new LinkedList<>();
+			Queue<MessageId> toShare = new LinkedList<>(
-			Transaction txn = db.startTransaction(true);
+					db.transactionWithResult(true, db::getMessagesToShare));
-			try {
-				toShare.addAll(db.getMessagesToShare(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
 			shareNextMessageAsync(toShare);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -387,15 +360,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void shareNextMessage(Queue<MessageId> toShare) {
 		try {
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				MessageId id = toShare.poll();
+				if (id == null) throw new AssertionError();
 				db.setMessageShared(txn, id);
 				toShare.addAll(db.getMessageDependencies(txn, id).keySet());
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 			shareNextMessageAsync(toShare);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before sharing");
@@ -416,17 +386,14 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void invalidateNextMessage(Queue<MessageId> invalidate) {
 		try {
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				MessageId id = invalidate.poll();
+				if (id == null) throw new AssertionError();
 				if (db.getMessageState(txn, id) != INVALID) {
 					invalidateMessage(txn, id);
-					invalidate.addAll(getDependentsToInvalidate(txn, id));
+					addDependentsToInvalidate(txn, id, invalidate);
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 			invalidateNextMessageAsync(invalidate);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before invalidation");
@@ -445,14 +412,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	}
 
 	@DatabaseExecutor
-	private Queue<MessageId> getDependentsToInvalidate(Transaction txn,
+	private void addDependentsToInvalidate(Transaction txn,
-			MessageId m) throws DbException {
+			MessageId m, Queue<MessageId> invalidate) throws DbException {
-		Queue<MessageId> invalidate = new LinkedList<>();
+		Map<MessageId, MessageState> states = db.getMessageDependents(txn, m);
-		Map<MessageId, State> states = db.getMessageDependents(txn, m);
+		for (Entry<MessageId, MessageState> e : states.entrySet()) {
-		for (Entry<MessageId, State> e : states.entrySet()) {
 			if (e.getValue() != INVALID) invalidate.add(e.getKey());
 		}
-		return invalidate;
 	}
 
 	@Override
@@ -472,14 +437,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void loadGroupAndValidate(Message m) {
 		try {
-			Group g;
+			Group g = db.transactionWithResult(true, txn ->
-			Transaction txn = db.startTransaction(true);
+					db.getGroup(txn, m.getGroupId()));
-			try {
-				g = db.getGroup(txn, m.getGroupId());
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
 			validateMessageAsync(m, g);
 		} catch (NoSuchGroupException e) {
 			LOG.info("Group removed before validation");

bramble-core/src/main/java/org/briarproject/bramble/sync/validation/ValidationModule.java

@@ -0,0 +1,53 @@
+package org.briarproject.bramble.sync.validation;
+
+import org.briarproject.bramble.PoliteExecutor;
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ValidationModule {
+
+	public static class EagerSingletons {
+		@Inject
+		ValidationManager validationManager;
+	}
+
+	/**
+	 * The maximum number of validation tasks to delegate to the crypto
+	 * executor concurrently.
+	 * <p>
+	 * The number of available processors can change during the lifetime of the
+	 * JVM, so this is just a reasonable guess.
+	 */
+	private static final int MAX_CONCURRENT_VALIDATION_TASKS =
+			Math.max(1, Runtime.getRuntime().availableProcessors() - 1);
+
+	@Provides
+	@Singleton
+	ValidationManager provideValidationManager(
+			LifecycleManager lifecycleManager, EventBus eventBus,
+			ValidationManagerImpl validationManager) {
+		lifecycleManager.registerService(validationManager);
+		eventBus.addListener(validationManager);
+		return validationManager;
+	}
+
+	@Provides
+	@Singleton
+	@ValidationExecutor
+	Executor provideValidationExecutor(
+			@CryptoExecutor Executor cryptoExecutor) {
+		return new PoliteExecutor("ValidationExecutor", cryptoExecutor,
+				MAX_CONCURRENT_VALIDATION_TASKS);
+	}
+}

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

@@ -13,32 +13,33 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.Immutable;
 
 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 LinuxSecureRandomProvider extends AbstractSecureRandomProvider {
+class UnixSecureRandomProvider extends AbstractSecureRandomProvider {
 
 	private static final Logger LOG =
-			Logger.getLogger(LinuxSecureRandomProvider.class.getName());
+			getLogger(UnixSecureRandomProvider.class.getName());
 
 	private static final File RANDOM_DEVICE = new File("/dev/urandom");
 
 	private final AtomicBoolean seeded = new AtomicBoolean(false);
 	private final File outputDevice;
 
-	LinuxSecureRandomProvider() {
+	UnixSecureRandomProvider() {
 		this(RANDOM_DEVICE);
 	}
 
-	LinuxSecureRandomProvider(File outputDevice) {
+	UnixSecureRandomProvider(File outputDevice) {
 		this.outputDevice = outputDevice;
 	}
 
 	@Override
 	public Provider getProvider() {
 		if (!seeded.getAndSet(true)) writeSeed();
-		return new LinuxProvider();
+		return new UnixProvider();
 	}
 
 	protected void writeSeed() {
@@ -55,15 +56,15 @@ class LinuxSecureRandomProvider extends AbstractSecureRandomProvider {
 	}
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
-	private static class LinuxProvider extends Provider {
+	private static class UnixProvider extends Provider {
 
-		private LinuxProvider() {
+		private UnixProvider() {
-			super("LinuxPRNG", 1.1, "A Linux-specific PRNG using /dev/urandom");
+			super("UnixPRNG", 1.0, "A Unix-specific PRNG using /dev/urandom");
 			// Although /dev/urandom is not a SHA-1 PRNG, some callers
 			// explicitly request a SHA1PRNG SecureRandom and we need to
 			// prevent them from getting the default implementation whose
 			// output may have low entropy.
-			put("SecureRandom.SHA1PRNG", LinuxSecureRandomSpi.class.getName());
+			put("SecureRandom.SHA1PRNG", UnixSecureRandomSpi.class.getName());
 			put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
 		}
 	}

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

@@ -10,22 +10,24 @@ import java.security.SecureRandomSpi;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
-public class LinuxSecureRandomSpi extends SecureRandomSpi {
+public class UnixSecureRandomSpi extends SecureRandomSpi {
 
 	private static final Logger LOG =
-			Logger.getLogger(LinuxSecureRandomSpi.class.getName());
+			getLogger(UnixSecureRandomSpi.class.getName());
 
 	private static final File RANDOM_DEVICE = new File("/dev/urandom");
 
 	private final File inputDevice, outputDevice;
 
-	public LinuxSecureRandomSpi() {
+	@SuppressWarnings("WeakerAccess")
+	public UnixSecureRandomSpi() {
 		this(RANDOM_DEVICE, RANDOM_DEVICE);
 	}
 
-	LinuxSecureRandomSpi(File inputDevice, File outputDevice) {
+	UnixSecureRandomSpi(File inputDevice, File outputDevice) {
 		this.inputDevice = inputDevice;
 		this.outputDevice = outputDevice;
 	}

bramble-core/src/main/java/org/briarproject/bramble/transport/KeyManagerImpl.java

@@ -72,8 +72,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 		for (DuplexPluginFactory f : pluginConfig.getDuplexFactories())
 			transports.put(f.getId(), f.getMaxLatency());
 		try {
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				for (Contact c : db.getContacts(txn))
 					if (c.isActive()) activeContacts.put(c.getId(), true);
 				for (Entry<TransportId, Integer> e : transports.entrySet())
@@ -85,10 +84,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 					managers.put(e.getKey(), m);
 					m.start(txn);
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 		} catch (DbException e) {
 			throw new ServiceException(e);
 		}
@@ -141,15 +137,8 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx;
+		return db.transactionWithNullableResult(false, txn ->
-		Transaction txn = db.startTransaction(false);
+				m.getStreamContext(txn, c));
-		try {
-			ctx = m.getStreamContext(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return ctx;
 	}
 
 	@Override
@@ -160,15 +149,8 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx;
+		return db.transactionWithNullableResult(false, txn ->
-		Transaction txn = db.startTransaction(false);
+				m.getStreamContext(txn, tag));
-		try {
-			ctx = m.getStreamContext(txn, tag);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return ctx;
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManagerImpl.java

@@ -162,13 +162,7 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 	private void rotateKeys() {
 		dbExecutor.execute(() -> {
 			try {
-				Transaction txn = db.startTransaction(false);
+				db.transaction(false, this::rotateKeys);
-				try {
-					rotateKeys(txn);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 			}

bramble-core/src/main/java/org/briarproject/bramble/versioning/ClientVersioningManagerImpl.java

@@ -23,7 +23,7 @@ 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.ValidationManager.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientMajorVersion;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
@@ -89,14 +89,9 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 	public Visibility getClientVisibility(Transaction txn, ContactId contactId,
 			ClientId clientId, int majorVersion) throws DbException {
 		try {
-			Contact contact = db.getContact(txn, contactId);
+			LatestUpdates latest = findLatestUpdates(txn, contactId);
-			Group g = getContactGroup(contact);
+			if (latest == null || latest.remote == null) return INVISIBLE;
-			// Contact may be in the process of being added or removed, so
-			// contact group may not exist
-			if (!db.containsGroup(txn, g.getId())) return INVISIBLE;
-			LatestUpdates latest = findLatestUpdates(txn, g.getId());
 			if (latest.local == null) throw new DbException();
-			if (latest.remote == null) return INVISIBLE;
 			Update localUpdate = loadUpdate(txn, latest.local.messageId);
 			Update remoteUpdate = loadUpdate(txn, latest.remote.messageId);
 			Map<ClientMajorVersion, Visibility> visibilities =
@@ -110,6 +105,24 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 		}
 	}
 
+	@Override
+	public int getClientMinorVersion(Transaction txn, ContactId contactId,
+			ClientId clientId, int majorVersion) throws DbException {
+		try {
+			LatestUpdates latest = findLatestUpdates(txn, contactId);
+			if (latest == null || latest.remote == null) return -1;
+			Update remoteUpdate = loadUpdate(txn, latest.remote.messageId);
+			ClientMajorVersion cv =
+					new ClientMajorVersion(clientId, majorVersion);
+			for (ClientState remote : remoteUpdate.states) {
+				if (remote.majorVersion.equals(cv)) return remote.minorVersion;
+			}
+			return -1;
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void createLocalState(Transaction txn) throws DbException {
 		if (db.containsGroup(txn, localGroup.getId())) return;
@@ -123,16 +136,12 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 		List<ClientVersion> versions = new ArrayList<>(clients);
 		Collections.sort(versions);
 		try {
-			Transaction txn = db.startTransaction(false);
+			db.transaction(false, txn -> {
-			try {
 				if (updateClientVersions(txn, versions)) {
 					for (Contact c : db.getContacts(txn))
 						clientVersionsUpdated(txn, c, versions);
 				}
-				db.commitTransaction(txn);
+			});
-			} finally {
-				db.endTransaction(txn);
-			}
 		} catch (DbException e) {
 			throw new ServiceException(e);
 		}
@@ -340,6 +349,17 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 				MAJOR_VERSION, c);
 	}
 
+	@Nullable
+	private LatestUpdates findLatestUpdates(Transaction txn, ContactId c)
+			throws DbException, FormatException {
+		Contact contact = db.getContact(txn, c);
+		Group g = getContactGroup(contact);
+		// Contact may be in the process of being added or removed, so
+		// contact group may not exist
+		if (!db.containsGroup(txn, g.getId())) return null;
+		return findLatestUpdates(txn, g.getId());
+	}
+
 	private LatestUpdates findLatestUpdates(Transaction txn, GroupId g)
 			throws DbException, FormatException {
 		Map<MessageId, BdfDictionary> metadata =

bramble-core/src/main/java/org/briarproject/bramble/versioning/VersioningModule.java

@@ -4,7 +4,7 @@ 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.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.sync.ValidationManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 

bramble-core/src/main/resources/bridges

@@ -1,8 +1,4 @@
-Bridge 131.252.210.150:8081 0E858AC201BF0F3FA3C462F64844CBFFC7297A42
+Bridge obfs4 78.46.188.239:37356 5A2D2F4158D0453E00C7C176978D3F41D69C45DB cert=3c0SwxpOisbohNxEc4tb875RVW8eOu1opRTVXJhafaKA/PNNtI7ElQIVOVZg1AdL5bxGCw iat-mode=0
-Bridge 67.205.189.122:8443 12D64D5D44E20169585E7378580C0D33A872AD98
+Bridge obfs4 52.15.78.72:9443 02069A3C5362476936B62BA6F5ACC41ABD573A9B cert=ijYG/OKc7kqu2YzKNFfeXN7/BG2BOgfEP2KyYEiGDQthnHbsOiTWHeIG0WJVW+BckzDgKw iat-mode=0
-Bridge 45.32.148.146:8443 0CE016FB2462D8BF179AE71F7D702D09DEAC3F1D
+Bridge obfs4 13.58.29.242:9443 0C58939A77DA6B6B29D4B5236A75865659607AE0 cert=OylWIEHb/ezpq1zWxW0sgKRn+9ARH2eOcQOZ8/Gew+4l+oKOhQ2jUX/Y+FSl61JorXZUWA iat-mode=0
-Bridge 148.251.90.59:7510 019F727CA6DCA6CA5C90B55E477B7D87981E75BC
+Bridge obfs4 45.33.37.112:9443 60A609BB4ABE8D46E634AE81ED29ADAB7776B399 cert=t5v19WmNv5Sc2YPNr8RQids365W7MY8zJwQVkOxBjUMFomMWARDzsbYpcWLLcw0J9Gm+BQ iat-mode=0
-Bridge 45.55.1.74:8443 6F18FEFBB0CAECD5ABA755312FCCB34FC11A7AB8
-Bridge 85.229.131.78:444 50E433CCC5FEC11CC34CB4D92033561E065EA106
-Bridge 178.62.62.193:8443 391B1F9B6A28A1C5FAE1872283985F975E5DB029
-Bridge 45.76.29.92:8443 ECF1DD51A46FDEF2C50CED992EEEAE8DED18DA0C

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

@@ -0,0 +1,86 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.Vector;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+
+import static java.util.Arrays.asList;
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class PriorityExecutorTest extends BrambleTestCase {
+
+	@Test
+	public void testHighPriorityTasksAreDelegatedInOrderOfSubmission()
+			throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor high = priority.getHighPriorityExecutor();
+		testTasksAreDelegatedInOrderOfSubmission(high);
+	}
+
+	@Test
+	public void testLowPriorityTasksAreDelegatedInOrderOfSubmission()
+			throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor low = priority.getLowPriorityExecutor();
+		testTasksAreDelegatedInOrderOfSubmission(low);
+	}
+
+	@Test
+	public void testHighPriorityTasksAreRunFirst() throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor high = priority.getHighPriorityExecutor();
+		Executor low = priority.getLowPriorityExecutor();
+		// Submit a task that will block, causing other tasks to be queued
+		CountDownLatch cork = new CountDownLatch(1);
+		low.execute(() -> {
+			try {
+				cork.await();
+			} catch (InterruptedException e) {
+				fail();
+			}
+		});
+		// Submit alternating tasks to the high and low priority executors
+		List<Integer> results = new Vector<>();
+		CountDownLatch tasksFinished = new CountDownLatch(10);
+		for (int i = 0; i < 10; i++) {
+			int result = i;
+			Runnable task = () -> {
+				results.add(result);
+				tasksFinished.countDown();
+			};
+			if (i % 2 == 0) high.execute(task);
+			else low.execute(task);
+		}
+		// Release the cork and wait for all tasks to finish
+		cork.countDown();
+		tasksFinished.await();
+		// The high-priority tasks should have run before the low-priority tasks
+		assertEquals(asList(0, 2, 4, 6, 8, 1, 3, 5, 7, 9), results);
+	}
+
+	private void testTasksAreDelegatedInOrderOfSubmission(Executor e)
+			throws Exception {
+		List<Integer> results = new Vector<>();
+		CountDownLatch tasksFinished = new CountDownLatch(10);
+		for (int i = 0; i < 10; i++) {
+			int result = i;
+			e.execute(() -> {
+				results.add(result);
+				tasksFinished.countDown();
+			});
+		}
+		// Wait for all the tasks to finish
+		tasksFinished.await();
+		// The tasks should have run in the order they were submitted
+		assertEquals(asList(0, 1, 2, 3, 4, 5, 6, 7, 8, 9), results);
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/client/ClientHelperImplTest.java

@@ -22,6 +22,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.test.BrambleTestCase;
+import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.util.StringUtils;
 import org.jmock.Expectations;
 import org.jmock.Mockery;
@@ -85,14 +86,11 @@ public class ClientHelperImplTest extends BrambleTestCase {
 		boolean shared = new Random().nextBoolean();
 		Transaction txn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			oneOf(metadataEncoder).encode(dictionary);
 			will(returnValue(metadata));
 			oneOf(db).addLocalMessage(txn, message, metadata, shared);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		clientHelper.addLocalMessage(message, dictionary, shared);
@@ -116,13 +114,10 @@ public class ClientHelperImplTest extends BrambleTestCase {
 		Transaction txn = new Transaction(null, true);
 
 		expectToList(true);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessage(txn, messageId);
 			will(returnValue(message));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		clientHelper.getMessageAsList(messageId);
@@ -133,15 +128,12 @@ public class ClientHelperImplTest extends BrambleTestCase {
 	public void testGetGroupMetadataAsDictionary() throws Exception {
 		Transaction txn = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroupMetadata(txn, groupId);
 			will(returnValue(metadata));
 			oneOf(metadataParser).parse(metadata);
 			will(returnValue(dictionary));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(dictionary,
@@ -153,15 +145,12 @@ public class ClientHelperImplTest extends BrambleTestCase {
 	public void testGetMessageMetadataAsDictionary() throws Exception {
 		Transaction txn = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessageMetadata(txn, messageId);
 			will(returnValue(metadata));
 			oneOf(metadataParser).parse(metadata);
 			will(returnValue(dictionary));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(dictionary,
@@ -175,15 +164,12 @@ public class ClientHelperImplTest extends BrambleTestCase {
 		map.put(messageId, dictionary);
 		Transaction txn = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessageMetadata(txn, groupId);
 			will(returnValue(Collections.singletonMap(messageId, metadata)));
 			oneOf(metadataParser).parse(metadata);
 			will(returnValue(dictionary));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(map, clientHelper.getMessageMetadataAsDictionary(groupId));
@@ -200,17 +186,14 @@ public class ClientHelperImplTest extends BrambleTestCase {
 		queryMetadata.put("query", getRandomBytes(42));
 		Transaction txn = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(metadataEncoder).encode(query);
 			will(returnValue(queryMetadata));
 			oneOf(db).getMessageMetadata(txn, groupId, queryMetadata);
 			will(returnValue(Collections.singletonMap(messageId, metadata)));
 			oneOf(metadataParser).parse(metadata);
 			will(returnValue(dictionary));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(map,
@@ -222,14 +205,11 @@ public class ClientHelperImplTest extends BrambleTestCase {
 	public void testMergeGroupMetadata() throws Exception {
 		Transaction txn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			oneOf(metadataEncoder).encode(dictionary);
 			will(returnValue(metadata));
 			oneOf(db).mergeGroupMetadata(txn, groupId, metadata);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		clientHelper.mergeGroupMetadata(groupId, dictionary);
@@ -240,14 +220,11 @@ public class ClientHelperImplTest extends BrambleTestCase {
 	public void testMergeMessageMetadata() throws Exception {
 		Transaction txn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			oneOf(metadataEncoder).encode(dictionary);
 			will(returnValue(metadata));
 			oneOf(db).mergeMessageMetadata(txn, messageId, metadata);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		clientHelper.mergeMessageMetadata(messageId, dictionary);

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

@@ -69,17 +69,14 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 		boolean alice = new Random().nextBoolean();
 		Transaction txn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithResult(with(false), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).addContact(txn, remote, local, verified, active);
 			will(returnValue(contactId));
 			oneOf(keyManager).addContact(txn, contactId, master, timestamp,
 					alice, active);
 			oneOf(db).getContact(txn, contactId);
 			will(returnValue(contact));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(contactId, contactManager.addContact(remote, local,
@@ -89,13 +86,10 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	@Test
 	public void testGetContact() throws Exception {
 		Transaction txn = new Transaction(null, true);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContact(txn, contactId);
 			will(returnValue(contact));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(contact, contactManager.getContact(contactId));
@@ -105,13 +99,10 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	public void testGetContactByAuthor() throws Exception {
 		Transaction txn = new Transaction(null, true);
 		Collection<Contact> contacts = Collections.singleton(contact);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContactsByAuthorId(txn, remote.getId());
 			will(returnValue(contacts));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(contact, contactManager.getContact(remote.getId(), local));
@@ -120,12 +111,10 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	@Test(expected = NoSuchContactException.class)
 	public void testGetContactByUnknownAuthor() throws Exception {
 		Transaction txn = new Transaction(null, true);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContactsByAuthorId(txn, remote.getId());
 			will(returnValue(emptyList()));
-			oneOf(db).endTransaction(txn);
 		}});
 
 		contactManager.getContact(remote.getId(), local);
@@ -135,31 +124,26 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	public void testGetContactByUnknownLocalAuthor() throws Exception {
 		Transaction txn = new Transaction(null, true);
 		Collection<Contact> contacts = Collections.singleton(contact);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContactsByAuthorId(txn, remote.getId());
 			will(returnValue(contacts));
-			oneOf(db).endTransaction(txn);
 		}});
 
 		contactManager.getContact(remote.getId(), new AuthorId(getRandomId()));
 	}
 
 	@Test
-	public void testActiveContacts() throws Exception {
+	public void testGetActiveContacts() throws Exception {
 		Collection<Contact> activeContacts = Collections.singletonList(contact);
 		Collection<Contact> contacts = new ArrayList<>(activeContacts);
 		contacts.add(new Contact(new ContactId(3), remote, local, alias, true,
 				false));
 		Transaction txn = new Transaction(null, true);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContacts(txn);
 			will(returnValue(contacts));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertEquals(activeContacts, contactManager.getActiveContacts());
@@ -168,14 +152,11 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	@Test
 	public void testRemoveContact() throws Exception {
 		Transaction txn = new Transaction(null, false);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContact(txn, contactId);
 			will(returnValue(contact));
 			oneOf(db).removeContact(txn, contactId);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		contactManager.removeContact(contactId);
@@ -195,7 +176,7 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	public void testSetContactAlias() throws Exception {
 		Transaction txn = new Transaction(null, false);
 		context.checking(new DbExpectations() {{
-			oneOf(db).transaction(with(equal(false)), withDbRunnable(txn));
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
 			oneOf(db).setContactAlias(txn, contactId, alias);
 		}});
 
@@ -204,35 +185,32 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 
 	@Test(expected = IllegalArgumentException.class)
 	public void testSetContactAliasTooLong() throws Exception {
-		contactManager.setContactAlias(contactId,
+		Transaction txn = new Transaction(null, false);
+		contactManager.setContactAlias(txn, contactId,
 				getRandomString(MAX_AUTHOR_NAME_LENGTH + 1));
 	}
 
 	@Test
 	public void testContactExists() throws Exception {
 		Transaction txn = new Transaction(null, true);
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).containsContact(txn, remote.getId(), local);
 			will(returnValue(true));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		assertTrue(contactManager.contactExists(remote.getId(), local));
 	}
 
 	@Test
-	public void testGetAuthorStatus() throws Exception {
+	public void testGetAuthorInfo() throws Exception {
 		Transaction txn = new Transaction(null, true);
 		Collection<Contact> contacts = singletonList(
 				new Contact(new ContactId(1), remote, localAuthor.getId(),
 						alias, false, true));
 
 		context.checking(new DbExpectations() {{
-			oneOf(db).transactionWithResult(with(equal(true)),
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-					withDbCallable(txn));
 			oneOf(identityManager).getLocalAuthor(txn);
 			will(returnValue(localAuthor));
 			oneOf(db).getContactsByAuthorId(txn, remote.getId());
@@ -245,7 +223,7 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testGetAuthorStatusTransaction() throws DbException {
+	public void testGetAuthorInfoTransaction() throws DbException {
 		Transaction txn = new Transaction(null, true);
 
 		// check unknown author
@@ -264,7 +242,7 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 		Collection<Contact> contacts = singletonList(
 				new Contact(new ContactId(1), remote, localAuthor.getId(),
 						alias, false, true));
-		checkAuthorStatusContext(txn, remote.getId(), contacts);
+		checkAuthorInfoContext(txn, remote.getId(), contacts);
 		authorInfo = contactManager.getAuthorInfo(txn, remote.getId());
 		assertEquals(UNVERIFIED, authorInfo.getStatus());
 		assertEquals(alias, contact.getAlias());
@@ -272,7 +250,7 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 		// check verified contact
 		contacts = singletonList(new Contact(new ContactId(1), remote,
 				localAuthor.getId(), alias, true, true));
-		checkAuthorStatusContext(txn, remote.getId(), contacts);
+		checkAuthorInfoContext(txn, remote.getId(), contacts);
 		authorInfo = contactManager.getAuthorInfo(txn, remote.getId());
 		assertEquals(VERIFIED, authorInfo.getStatus());
 		assertEquals(alias, contact.getAlias());
@@ -288,7 +266,7 @@ public class ContactManagerImplTest extends BrambleMockTestCase {
 		assertNull(authorInfo.getAlias());
 	}
 
-	private void checkAuthorStatusContext(Transaction txn, AuthorId authorId,
+	private void checkAuthorInfoContext(Transaction txn, AuthorId authorId,
 			Collection<Contact> contacts) throws DbException {
 		context.checking(new Expectations() {{
 			oneOf(identityManager).getLocalAuthor(txn);

bramble-core/src/test/java/org/briarproject/bramble/data/BdfReaderImplFuzzingTest.java

@@ -0,0 +1,41 @@
+package org.briarproject.bramble.data;
+
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.ByteArrayInputStream;
+import java.util.Random;
+
+import static org.briarproject.bramble.api.data.BdfReader.DEFAULT_MAX_BUFFER_SIZE;
+import static org.briarproject.bramble.api.data.BdfReader.DEFAULT_NESTED_LIMIT;
+import static org.briarproject.bramble.test.TestUtils.isOptionalTestEnabled;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
+
+public class BdfReaderImplFuzzingTest extends BrambleTestCase {
+
+	@Before
+	public void setUp() {
+		assumeTrue(isOptionalTestEnabled(BdfReaderImplFuzzingTest.class));
+	}
+
+	@Test
+	public void testStringFuzzing() throws Exception {
+		Random random = new Random();
+		byte[] buf = new byte[22];
+		ByteArrayInputStream in = new ByteArrayInputStream(buf);
+		for (int i = 0; i < 100_000_000; i++) {
+			random.nextBytes(buf);
+			buf[0] = 0x41; // String with 1-byte length
+			buf[1] = 0x14; // Length 20 bytes
+			in.reset();
+			BdfReaderImpl r = new BdfReaderImpl(in, DEFAULT_NESTED_LIMIT,
+					DEFAULT_MAX_BUFFER_SIZE);
+			int length = r.readString().length();
+			assertTrue(length >= 0);
+			assertTrue(length <= 20);
+			assertTrue(r.eof());
+		}
+	}
+}

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

@@ -11,7 +11,7 @@ import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.UTest;
 import org.junit.After;
@@ -33,7 +33,7 @@ import java.util.logging.Logger;
 
 import static java.util.logging.Level.OFF;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
 import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
 import static org.briarproject.bramble.test.TestUtils.getAuthor;
 import static org.briarproject.bramble.test.TestUtils.getGroup;
@@ -565,7 +565,8 @@ public abstract class DatabasePerformanceTest extends BrambleTestCase {
 				for (int k = 0; k < MESSAGES_PER_GROUP; k++) {
 					Message m = getMessage(g.getId());
 					messages.add(m);
-					State state = State.fromValue(random.nextInt(4));
+					MessageState state =
+							MessageState.fromValue(random.nextInt(4));
 					boolean shared = random.nextBoolean();
 					ContactId sender = random.nextBoolean() ? c : null;
 					db.addMessage(txn, m, state, shared, sender);

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

@@ -18,7 +18,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.KeySet;
@@ -58,10 +58,10 @@ import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
+import static org.briarproject.bramble.api.sync.validation.MessageState.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
+import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+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.LAST_COMPACTED_KEY;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_COMPACTION_INTERVAL_MS;
@@ -1309,7 +1309,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessageDependency(txn, message1, messageId3, PENDING);
 		db.addMessageDependency(txn, message2, messageId4, INVALID);
 
-		Map<MessageId, State> dependencies;
+		Map<MessageId, MessageState> dependencies;
 
 		// Retrieve dependencies for root
 		dependencies = db.getMessageDependencies(txn, messageId);
@@ -1333,7 +1333,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		dependencies = db.getMessageDependencies(txn, messageId4);
 		assertEquals(0, dependencies.size());
 
-		Map<MessageId, State> dependents;
+		Map<MessageId, MessageState> dependents;
 
 		// Root message does not have dependents
 		dependents = db.getMessageDependents(txn, messageId);
@@ -1408,7 +1408,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessageDependency(txn, message, messageId3, PENDING);
 
 		// Retrieve the dependencies for the root
-		Map<MessageId, State> dependencies;
+		Map<MessageId, MessageState> dependencies;
 		dependencies = db.getMessageDependencies(txn, messageId);
 
 		// The cross-group dependency should have state UNKNOWN
@@ -1421,7 +1421,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertEquals(DELIVERED, dependencies.get(messageId3));
 
 		// Retrieve the dependents for the message in the second group
-		Map<MessageId, State> dependents;
+		Map<MessageId, MessageState> dependents;
 		dependents = db.getMessageDependents(txn, messageId1);
 
 		// The cross-group dependent should be excluded

bramble-core/src/test/java/org/briarproject/bramble/identity/IdentityManagerImplTest.java

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.identity.AuthorFactory;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.DbExpectations;
 import org.jmock.Expectations;
 import org.junit.Before;
 import org.junit.Test;
@@ -64,13 +65,10 @@ public class IdentityManagerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testRegisterAndStoreLocalAuthor() throws DbException {
+	public void testRegisterAndStoreLocalAuthor() throws Exception {
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			oneOf(db).addLocalAuthor(txn, localAuthor);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		identityManager.registerLocalAuthor(localAuthor);
@@ -79,14 +77,11 @@ public class IdentityManagerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testGetLocalAuthor() throws DbException {
+	public void testGetLocalAuthor() throws Exception {
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getLocalAuthors(txn);
 			will(returnValue(localAuthors));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 		assertEquals(localAuthor, identityManager.getLocalAuthor());
 	}

bramble-core/src/test/java/org/briarproject/bramble/properties/TransportPropertyManagerImplTest.java

@@ -21,16 +21,18 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.DbExpectations;
 import org.jmock.Expectations;
 import org.junit.Test;
 
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Arrays.asList;
 import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.properties.TransportPropertyManager.CLIENT_ID;
 import static org.briarproject.bramble.api.properties.TransportPropertyManager.MAJOR_VERSION;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
@@ -351,14 +353,11 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 				new BdfEntry("local", true)
 		));
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
 					localGroup.getId());
 			will(returnValue(messageMetadata));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
@@ -386,9 +385,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		));
 		BdfList fooUpdate = BdfList.of("foo", 1, fooPropertiesDict);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
 					localGroup.getId());
 			will(returnValue(messageMetadata));
@@ -397,8 +395,6 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 			oneOf(clientHelper).parseAndValidateTransportProperties(
 					fooPropertiesDict);
 			will(returnValue(fooProperties));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
@@ -413,8 +409,7 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		Contact contact1 = getContact(false);
 		Contact contact2 = getContact(true);
 		Contact contact3 = getContact(true);
-		List<Contact> contacts =
+		List<Contact> contacts = asList(contact1, contact2, contact3);
-				Arrays.asList(contact1, contact2, contact3);
 		Group contactGroup2 = getGroup(CLIENT_ID, MAJOR_VERSION);
 		Group contactGroup3 = getGroup(CLIENT_ID, MAJOR_VERSION);
 		Map<MessageId, BdfDictionary> messageMetadata3 =
@@ -442,9 +437,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		));
 		BdfList fooUpdate = BdfList.of("foo", 1, fooPropertiesDict);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getContacts(txn);
 			will(returnValue(contacts));
 			// First contact: skipped because not active
@@ -467,8 +461,6 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 			oneOf(clientHelper).parseAndValidateTransportProperties(
 					fooPropertiesDict);
 			will(returnValue(fooProperties));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
@@ -485,17 +477,16 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 			throws Exception {
 		Transaction txn = new Transaction(null, false);
 		MessageId updateId = new MessageId(getRandomId());
-		Map<MessageId, BdfDictionary> messageMetadata =
+		Map<MessageId, BdfDictionary> messageMetadata = singletonMap(updateId,
-				Collections.singletonMap(updateId, BdfDictionary.of(
+				BdfDictionary.of(
 						new BdfEntry("transportId", "foo"),
 						new BdfEntry("version", 1),
 						new BdfEntry("local", true)
 				));
 		BdfList update = BdfList.of("foo", 1, fooPropertiesDict);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			// Merge the new properties with the existing properties
 			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
 					localGroup.getId());
@@ -506,8 +497,6 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 					fooPropertiesDict);
 			will(returnValue(fooProperties));
 			// Properties are unchanged so we're done
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
@@ -520,9 +509,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		Contact contact = getContact(true);
 		Group contactGroup = getGroup(CLIENT_ID, MAJOR_VERSION);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			// There are no existing properties to merge with
 			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
 					localGroup.getId());
@@ -541,8 +529,6 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(Collections.emptyMap()));
 			expectStoreMessage(txn, contactGroup.getId(), "foo",
 					fooPropertiesDict, 1, true, true);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
@@ -561,10 +547,10 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		);
 		MessageId localGroupUpdateId = new MessageId(getRandomId());
 		Map<MessageId, BdfDictionary> localGroupMessageMetadata =
-				Collections.singletonMap(localGroupUpdateId, oldMetadata);
+				singletonMap(localGroupUpdateId, oldMetadata);
 		MessageId contactGroupUpdateId = new MessageId(getRandomId());
 		Map<MessageId, BdfDictionary> contactGroupMessageMetadata =
-				Collections.singletonMap(contactGroupUpdateId, oldMetadata);
+				singletonMap(contactGroupUpdateId, oldMetadata);
 		TransportProperties oldProperties = new TransportProperties();
 		oldProperties.put("fooKey1", "oldFooValue1");
 		BdfDictionary oldPropertiesDict = BdfDictionary.of(
@@ -572,9 +558,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		);
 		BdfList oldUpdate = BdfList.of("foo", 1, oldPropertiesDict);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn));
-			will(returnValue(txn));
 			// Merge the new properties with the existing properties
 			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
 					localGroup.getId());
@@ -602,8 +587,6 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 					fooPropertiesDict, 2, true, true);
 			// Delete the previous update
 			oneOf(db).removeMessage(txn, contactGroupUpdateId);
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();

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

@@ -11,8 +11,8 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.transport.StreamWriter;
 import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.test.ImmediateExecutor;
-import org.jmock.Expectations;
 import org.junit.Test;
 
 import java.util.concurrent.Executor;
@@ -45,24 +45,20 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Add listener
 			oneOf(eventBus).addListener(session);
 			// No acks to send
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(noAckTxn));
+					withNullableDbCallable(noAckTxn));
 			oneOf(db).generateAck(noAckTxn, contactId, MAX_MESSAGE_IDS);
 			will(returnValue(null));
-			oneOf(db).commitTransaction(noAckTxn);
-			oneOf(db).endTransaction(noAckTxn);
 			// No messages to send
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(noMsgTxn));
+					withNullableDbCallable(noMsgTxn));
 			oneOf(db).generateBatch(with(noMsgTxn), with(contactId),
 					with(any(int.class)), with(MAX_LATENCY));
 			will(returnValue(null));
-			oneOf(db).commitTransaction(noMsgTxn);
-			oneOf(db).endTransaction(noMsgTxn);
 			// Send the end of stream marker
 			oneOf(streamWriter).sendEndOfStream();
 			// Remove listener
@@ -83,41 +79,33 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 		Transaction msgTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Add listener
 			oneOf(eventBus).addListener(session);
 			// One ack to send
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(ackTxn));
+					withNullableDbCallable(ackTxn));
 			oneOf(db).generateAck(ackTxn, contactId, MAX_MESSAGE_IDS);
 			will(returnValue(ack));
-			oneOf(db).commitTransaction(ackTxn);
-			oneOf(db).endTransaction(ackTxn);
 			oneOf(recordWriter).writeAck(ack);
 			// One message to send
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(msgTxn));
+					withNullableDbCallable(msgTxn));
 			oneOf(db).generateBatch(with(msgTxn), with(contactId),
 					with(any(int.class)), with(MAX_LATENCY));
 			will(returnValue(singletonList(message)));
-			oneOf(db).commitTransaction(msgTxn);
-			oneOf(db).endTransaction(msgTxn);
 			oneOf(recordWriter).writeMessage(message);
 			// No more acks
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(noAckTxn));
+					withNullableDbCallable(noAckTxn));
 			oneOf(db).generateAck(noAckTxn, contactId, MAX_MESSAGE_IDS);
 			will(returnValue(null));
-			oneOf(db).commitTransaction(noAckTxn);
-			oneOf(db).endTransaction(noAckTxn);
 			// No more messages
-			oneOf(db).startTransaction(false);
+			oneOf(db).transactionWithNullableResult(with(false),
-			will(returnValue(noMsgTxn));
+					withNullableDbCallable(noMsgTxn));
 			oneOf(db).generateBatch(with(noMsgTxn), with(contactId),
 					with(any(int.class)), with(MAX_LATENCY));
 			will(returnValue(null));
-			oneOf(db).commitTransaction(noMsgTxn);
-			oneOf(db).endTransaction(noMsgTxn);
 			// Send the end of stream marker
 			oneOf(streamWriter).sendEndOfStream();
 			// Remove listener

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

@@ -2,6 +2,7 @@ package org.briarproject.bramble.sync;
 
 import org.briarproject.bramble.crypto.CryptoModule;
 import org.briarproject.bramble.record.RecordModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.test.TestSecureRandomModule;
 import org.briarproject.bramble.transport.TransportModule;
@@ -17,6 +18,7 @@ import dagger.Component;
 		RecordModule.class,
 		SyncModule.class,
 		SystemModule.class,
+		ValidationModule.class,
 		TransportModule.class
 })
 interface SyncIntegrationTestComponent {

bramble-core/src/test/java/org/briarproject/bramble/sync/validation/ValidationManagerImplTest.java

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseComponent;
@@ -13,29 +13,29 @@ import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
-import org.briarproject.bramble.api.sync.ValidationManager.MessageValidator;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
 import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.MessageState;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
 import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.test.ImmediateExecutor;
-import org.jmock.Expectations;
 import org.junit.Before;
 import org.junit.Test;
 
-import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.concurrent.Executor;
 
+import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
+import static org.briarproject.bramble.api.sync.validation.MessageState.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
+import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.test.TestUtils.getClientId;
 import static org.briarproject.bramble.test.TestUtils.getGroup;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
@@ -83,28 +83,19 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn1 = new Transaction(null, true);
 		Transaction txn2 = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// validateOutstandingMessages()
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// deliverOutstandingMessages()
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getPendingMessages(txn1);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// shareOutstandingMessages()
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessagesToShare(txn2);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 		}});
 
 		vm.startService();
@@ -121,29 +112,22 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn5 = new Transaction(null, true);
 		Transaction txn6 = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Get messages to validate
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
-			will(returnValue(Arrays.asList(messageId, messageId1)));
+			will(returnValue(asList(messageId, messageId1)));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Load the first raw message and group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getMessage(txn1, messageId);
 			will(returnValue(message));
 			oneOf(db).getGroup(txn1, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Validate the first message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResult));
 			// Store the validation result for the first message
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).mergeMessageMetadata(txn2, messageId, metadata);
 			// Deliver the first message
 			oneOf(hook).incomingMessage(txn2, message, metadata);
@@ -152,23 +136,17 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn2, messageId);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Load the second raw message and group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessage(txn3, messageId1);
 			will(returnValue(message1));
 			oneOf(db).getGroup(txn3, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Validate the second message: invalid
 			oneOf(validator).validateMessage(message1, group);
 			will(throwException(new InvalidMessageException()));
 			// Store the validation result for the second message
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getMessageState(txn4, messageId1);
 			will(returnValue(UNKNOWN));
 			oneOf(db).setMessageState(txn4, messageId1, INVALID);
@@ -177,22 +155,14 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Recursively invalidate any dependents
 			oneOf(db).getMessageDependents(txn4, messageId1);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 			// Get pending messages to deliver
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn5));
-			will(returnValue(txn5));
 			oneOf(db).getPendingMessages(txn5);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn5);
-			oneOf(db).endTransaction(txn5);
 			// Get messages to share
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn6));
-			will(returnValue(txn6));
 			oneOf(db).getMessagesToShare(txn6);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn6);
-			oneOf(db).endTransaction(txn6);
 		}});
 
 		vm.startService();
@@ -206,24 +176,17 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn3 = new Transaction(null, false);
 		Transaction txn4 = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Get messages to validate
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Get pending messages to deliver
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getPendingMessages(txn1);
 			will(returnValue(singletonList(messageId)));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Check whether the message is ready to deliver
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessageState(txn2, messageId);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn2, messageId);
@@ -242,11 +205,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn2, messageId);
 			will(returnValue(singletonMap(messageId2, PENDING)));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Check whether the dependent is ready to deliver
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessageState(txn3, messageId2);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn3, messageId2);
@@ -265,16 +225,11 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn3, messageId2);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 
 			// Get messages to share
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getMessagesToShare(txn4);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 		}});
 
 		vm.startService();
@@ -288,45 +243,30 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn3 = new Transaction(null, false);
 		Transaction txn4 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// No messages to validate
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// No pending messages to deliver
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getPendingMessages(txn1);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 
 			// Get messages to share
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessagesToShare(txn2);
 			will(returnValue(singletonList(messageId)));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Share message and get dependencies
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).setMessageShared(txn3, messageId);
 			oneOf(db).getMessageDependencies(txn3, messageId);
 			will(returnValue(singletonMap(messageId2, DELIVERED)));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Share dependency
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).setMessageShared(txn4, messageId2);
 			oneOf(db).getMessageDependencies(txn4, messageId2);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 		}});
 
 		vm.startService();
@@ -338,20 +278,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn1 = new Transaction(null, false);
 		Transaction txn2 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResultWithDependencies));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).addMessageDependencies(txn1, message,
 					validResultWithDependencies.getDependencies());
 			oneOf(db).getMessageDependencies(txn1, messageId);
@@ -366,16 +302,11 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(emptyMap()));
 			// Share message
 			oneOf(db).setMessageShared(txn1, messageId);
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Share dependencies
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).setMessageShared(txn2, messageId1);
 			oneOf(db).getMessageDependencies(txn2, messageId1);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -391,36 +322,26 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn4 = new Transaction(null, true);
 		Transaction txn5 = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Get messages to validate
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
-			will(returnValue(Arrays.asList(messageId, messageId1)));
+			will(returnValue(asList(messageId, messageId1)));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Load the first raw message - *gasp* it's gone!
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getMessage(txn1, messageId);
 			will(throwException(new NoSuchMessageException()));
-			never(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Load the second raw message and group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessage(txn2, messageId1);
 			will(returnValue(message1));
 			oneOf(db).getGroup(txn2, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Validate the second message: invalid
 			oneOf(validator).validateMessage(message1, group);
 			will(throwException(new InvalidMessageException()));
 			// Invalidate the second message
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessageState(txn3, messageId1);
 			will(returnValue(UNKNOWN));
 			oneOf(db).setMessageState(txn3, messageId1, INVALID);
@@ -429,22 +350,14 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Recursively invalidate dependents
 			oneOf(db).getMessageDependents(txn3, messageId1);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Get pending messages to deliver
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getPendingMessages(txn4);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 			// Get messages to share
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn5));
-			will(returnValue(txn5));
 			oneOf(db).getMessagesToShare(txn5);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn5);
-			oneOf(db).endTransaction(txn5);
 		}});
 
 		vm.startService();
@@ -460,39 +373,29 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn4 = new Transaction(null, true);
 		Transaction txn5 = new Transaction(null, true);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Get messages to validate
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getMessagesToValidate(txn);
-			will(returnValue(Arrays.asList(messageId, messageId1)));
+			will(returnValue(asList(messageId, messageId1)));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Load the first raw message
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getMessage(txn1, messageId);
 			will(returnValue(message));
 			// Load the group - *gasp* it's gone!
 			oneOf(db).getGroup(txn1, groupId);
 			will(throwException(new NoSuchGroupException()));
-			never(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Load the second raw message and group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessage(txn2, messageId1);
 			will(returnValue(message1));
 			oneOf(db).getGroup(txn2, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Validate the second message: invalid
 			oneOf(validator).validateMessage(message1, group);
 			will(throwException(new InvalidMessageException()));
 			// Store the validation result for the second message
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessageState(txn3, messageId1);
 			will(returnValue(UNKNOWN));
 			oneOf(db).setMessageState(txn3, messageId1, INVALID);
@@ -501,22 +404,14 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Recursively invalidate dependents
 			oneOf(db).getMessageDependents(txn3, messageId1);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Get pending messages to deliver
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getPendingMessages(txn4);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 			// Get messages to share
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn5));
-			will(returnValue(txn5));
 			oneOf(db).getMessagesToShare(txn5);
 			will(returnValue(emptyList()));
-			oneOf(db).commitTransaction(txn5);
-			oneOf(db).endTransaction(txn5);
 		}});
 
 		vm.startService();
@@ -527,20 +422,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn = new Transaction(null, true);
 		Transaction txn1 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResult));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
@@ -549,8 +440,6 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -567,28 +456,22 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn = new Transaction(null, true);
 		Transaction txn1 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResultWithDependencies));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).addMessageDependencies(txn1, message,
 					validResultWithDependencies.getDependencies());
 			oneOf(db).getMessageDependencies(txn1, messageId);
 			will(returnValue(singletonMap(messageId1, UNKNOWN)));
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			oneOf(db).setMessageState(txn1, messageId, PENDING);
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -600,20 +483,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn = new Transaction(null, true);
 		Transaction txn1 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResultWithDependencies));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).addMessageDependencies(txn1, message,
 					validResultWithDependencies.getDependencies());
 			oneOf(db).getMessageDependencies(txn1, messageId);
@@ -626,8 +505,6 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -640,20 +517,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn1 = new Transaction(null, false);
 		Transaction txn2 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResultWithDependencies));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).addMessageDependencies(txn1, message,
 					validResultWithDependencies.getDependencies());
 			// Check for invalid dependencies
@@ -668,11 +541,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Recursively invalidate dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(singletonMap(messageId2, UNKNOWN)));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Invalidate dependent in a new transaction
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessageState(txn2, messageId2);
 			will(returnValue(UNKNOWN));
 			oneOf(db).setMessageState(txn2, messageId2, INVALID);
@@ -680,8 +550,6 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).deleteMessageMetadata(txn2, messageId2);
 			oneOf(db).getMessageDependents(txn2, messageId2);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -691,7 +559,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 	public void testRecursiveInvalidation() throws Exception {
 		MessageId messageId3 = new MessageId(getRandomId());
 		MessageId messageId4 = new MessageId(getRandomId());
-		Map<MessageId, State> twoDependents = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependents = new LinkedHashMap<>();
 		twoDependents.put(messageId1, PENDING);
 		twoDependents.put(messageId2, PENDING);
 		Transaction txn = new Transaction(null, true);
@@ -702,20 +570,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn5 = new Transaction(null, false);
 		Transaction txn6 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: invalid
 			oneOf(validator).validateMessage(message, group);
 			will(throwException(new InvalidMessageException()));
 			// Invalidate the message
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).getMessageState(txn1, messageId);
 			will(returnValue(UNKNOWN));
 			oneOf(db).setMessageState(txn1, messageId, INVALID);
@@ -724,11 +588,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// The message has two dependents: 1 and 2
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(twoDependents));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Invalidate message 1
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessageState(txn2, messageId1);
 			will(returnValue(PENDING));
 			oneOf(db).setMessageState(txn2, messageId1, INVALID);
@@ -737,11 +598,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 1 has one dependent: 3
 			oneOf(db).getMessageDependents(txn2, messageId1);
 			will(returnValue(singletonMap(messageId3, PENDING)));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Invalidate message 2
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessageState(txn3, messageId2);
 			will(returnValue(PENDING));
 			oneOf(db).setMessageState(txn3, messageId2, INVALID);
@@ -750,11 +608,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 2 has one dependent: 3 (same dependent as 1)
 			oneOf(db).getMessageDependents(txn3, messageId2);
 			will(returnValue(singletonMap(messageId3, PENDING)));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Invalidate message 3 (via 1)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getMessageState(txn4, messageId3);
 			will(returnValue(PENDING));
 			oneOf(db).setMessageState(txn4, messageId3, INVALID);
@@ -763,18 +618,12 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 3 has one dependent: 4
 			oneOf(db).getMessageDependents(txn4, messageId3);
 			will(returnValue(singletonMap(messageId4, PENDING)));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 			// Invalidate message 3 (again, via 2)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn5));
-			will(returnValue(txn5));
 			oneOf(db).getMessageState(txn5, messageId3);
 			will(returnValue(INVALID)); // Already invalidated
-			oneOf(db).commitTransaction(txn5);
-			oneOf(db).endTransaction(txn5);
 			// Invalidate message 4 (via 1 and 3)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn6));
-			will(returnValue(txn6));
 			oneOf(db).getMessageState(txn6, messageId4);
 			will(returnValue(PENDING));
 			oneOf(db).setMessageState(txn6, messageId4, INVALID);
@@ -783,8 +632,6 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 4 has no dependents
 			oneOf(db).getMessageDependents(txn6, messageId4);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn6);
-			oneOf(db).endTransaction(txn6);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -796,10 +643,10 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Message message4 = getMessage(groupId);
 		MessageId messageId3 = message3.getId();
 		MessageId messageId4 = message4.getId();
-		Map<MessageId, State> twoDependents = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependents = new LinkedHashMap<>();
 		twoDependents.put(messageId1, PENDING);
 		twoDependents.put(messageId2, PENDING);
-		Map<MessageId, State> twoDependencies = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependencies = new LinkedHashMap<>();
 		twoDependencies.put(messageId1, DELIVERED);
 		twoDependencies.put(messageId2, DELIVERED);
 		Transaction txn = new Transaction(null, true);
@@ -810,20 +657,16 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Transaction txn5 = new Transaction(null, false);
 		Transaction txn6 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResult));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
@@ -832,11 +675,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// The message has two pending dependents: 1 and 2
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(twoDependents));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Check whether message 1 is ready to be delivered
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessageState(txn2, messageId1);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn2, messageId1);
@@ -855,11 +695,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 1 has one pending dependent: 3
 			oneOf(db).getMessageDependents(txn2, messageId1);
 			will(returnValue(singletonMap(messageId3, PENDING)));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 			// Check whether message 2 is ready to be delivered
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn3));
-			will(returnValue(txn3));
 			oneOf(db).getMessageState(txn3, messageId2);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn3, messageId2);
@@ -878,11 +715,8 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 2 has one pending dependent: 3 (same dependent as 1)
 			oneOf(db).getMessageDependents(txn3, messageId2);
 			will(returnValue(singletonMap(messageId3, PENDING)));
-			oneOf(db).commitTransaction(txn3);
-			oneOf(db).endTransaction(txn3);
 			// Check whether message 3 is ready to be delivered (via 1)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn4));
-			will(returnValue(txn4));
 			oneOf(db).getMessageState(txn4, messageId3);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn4, messageId3);
@@ -900,18 +734,12 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 3 has one pending dependent: 4
 			oneOf(db).getMessageDependents(txn4, messageId3);
 			will(returnValue(singletonMap(messageId4, PENDING)));
-			oneOf(db).commitTransaction(txn4);
-			oneOf(db).endTransaction(txn4);
 			// Check whether message 3 is ready to be delivered (again, via 2)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn5));
-			will(returnValue(txn5));
 			oneOf(db).getMessageState(txn5, messageId3);
 			will(returnValue(DELIVERED)); // Already delivered
-			oneOf(db).commitTransaction(txn5);
-			oneOf(db).endTransaction(txn5);
 			// Check whether message 4 is ready to be delivered (via 1 and 3)
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn6));
-			will(returnValue(txn6));
 			oneOf(db).getMessageState(txn6, messageId4);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn6, messageId4);
@@ -930,8 +758,6 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Message 4 has no pending dependents
 			oneOf(db).getMessageDependents(txn6, messageId4);
 			will(returnValue(emptyMap()));
-			oneOf(db).commitTransaction(txn6);
-			oneOf(db).endTransaction(txn6);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));
@@ -939,27 +765,23 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 
 	@Test
 	public void testOnlyReadyPendingDependentsGetDelivered() throws Exception {
-		Map<MessageId, State> twoDependencies = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependencies = new LinkedHashMap<>();
 		twoDependencies.put(messageId, DELIVERED);
 		twoDependencies.put(messageId2, UNKNOWN);
 		Transaction txn = new Transaction(null, true);
 		Transaction txn1 = new Transaction(null, false);
 		Transaction txn2 = new Transaction(null, false);
 
-		context.checking(new Expectations() {{
+		context.checking(new DbExpectations() {{
 			// Load the group
-			oneOf(db).startTransaction(true);
+			oneOf(db).transactionWithResult(with(true), withDbCallable(txn));
-			will(returnValue(txn));
 			oneOf(db).getGroup(txn, groupId);
 			will(returnValue(group));
-			oneOf(db).commitTransaction(txn);
-			oneOf(db).endTransaction(txn);
 			// Validate the message: valid
 			oneOf(validator).validateMessage(message, group);
 			will(returnValue(validResult));
 			// Store the validation result
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn1));
-			will(returnValue(txn1));
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
@@ -968,17 +790,12 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
 			will(returnValue(singletonMap(messageId1, PENDING)));
-			oneOf(db).commitTransaction(txn1);
-			oneOf(db).endTransaction(txn1);
 			// Check whether the pending dependent is ready to be delivered
-			oneOf(db).startTransaction(false);
+			oneOf(db).transaction(with(false), withDbRunnable(txn2));
-			will(returnValue(txn2));
 			oneOf(db).getMessageState(txn2, messageId1);
 			will(returnValue(PENDING));
 			oneOf(db).getMessageDependencies(txn2, messageId1);
 			will(returnValue(twoDependencies));
-			oneOf(db).commitTransaction(txn2);
-			oneOf(db).endTransaction(txn2);
 		}});
 
 		vm.eventOccurred(new MessageAddedEvent(message, contactId));

bramble-core/src/test/java/org/briarproject/bramble/system/UnixSecureRandomProviderTest.java

@@ -1,8 +1,6 @@
 package org.briarproject.bramble.system;
 
 import org.briarproject.bramble.test.BrambleTestCase;
-import org.briarproject.bramble.test.TestUtils;
-import org.briarproject.bramble.util.OsUtils;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -10,48 +8,50 @@ import org.junit.Test;
 import java.io.File;
 import java.security.Provider;
 
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.briarproject.bramble.util.OsUtils.isLinux;
+import static org.briarproject.bramble.util.OsUtils.isMac;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
 
-public class LinuxSecureRandomProviderTest extends BrambleTestCase {
+public class UnixSecureRandomProviderTest extends BrambleTestCase {
 
-	private final File testDir = TestUtils.getTestDirectory();
+	private final File testDir = getTestDirectory();
 
 	@Before
 	public void setUp() {
-		testDir.mkdirs();
+		assumeTrue(isLinux() || isMac());
+		assertTrue(testDir.mkdirs());
 	}
 
 	@Test
 	public void testGetProviderWritesToRandomDeviceOnFirstCall()
 			throws Exception {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		// Redirect the provider's output to a file
 		File urandom = new File(testDir, "urandom");
-		urandom.delete();
+		if (urandom.exists()) assertTrue(urandom.delete());
 		assertTrue(urandom.createNewFile());
 		assertEquals(0, urandom.length());
-		LinuxSecureRandomProvider p = new LinuxSecureRandomProvider(urandom);
+		UnixSecureRandomProvider p = new UnixSecureRandomProvider(urandom);
 		// Getting a provider should write entropy to the file
 		Provider provider = p.getProvider();
 		assertNotNull(provider);
-		assertEquals("LinuxPRNG", provider.getName());
+		assertEquals("UnixPRNG", provider.getName());
 		// There should be at least 16 bytes from the clock, 8 from the runtime
 		long length = urandom.length();
 		assertTrue(length >= 24);
 		// Getting another provider should not write to the file again
 		provider = p.getProvider();
 		assertNotNull(provider);
-		assertEquals("LinuxPRNG", provider.getName());
+		assertEquals("UnixPRNG", provider.getName());
 		assertEquals(length, urandom.length());
 	}
 
 	@After
 	public void tearDown() {
-		TestUtils.deleteTestDirectory(testDir);
+		deleteTestDirectory(testDir);
 	}
 }