@GuardedBy annotations.

Add a setting to disable Tor when running on battery

Closes #978

See merge request briar/briar!1032

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

@@ -15,4 +15,8 @@ import dagger.Module;
 })
 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/account/AndroidAccountManager.java

@@ -9,19 +9,22 @@ import org.briarproject.bramble.api.account.AccountManager;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
-import org.briarproject.bramble.util.IoUtils;
 
 import java.io.File;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
+
 class AndroidAccountManager extends AccountManagerImpl
 		implements AccountManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidAccountManager.class.getName());
+			getLogger(AndroidAccountManager.class.getName());
 
 	private static final String PREF_DB_KEY = "key";
 
@@ -37,7 +40,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		appContext = app.getApplicationContext();
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Override
 	@Nullable
 	protected String loadEncryptedDatabaseKey() {
@@ -47,7 +50,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	private String getDatabaseKeyFromPreferences() {
 		String key = prefs.getString(PREF_DB_KEY, null);
@@ -56,7 +59,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void migrateDatabaseKeyToFile(String key) {
 		if (storeEncryptedDatabaseKey(key)) {
 			if (prefs.edit().remove(PREF_DB_KEY).commit())
@@ -81,7 +84,7 @@ class AndroidAccountManager extends AccountManagerImpl
 		return PreferenceManager.getDefaultSharedPreferences(appContext);
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void deleteAppData(SharedPreferences... clear) {
 		// Clear and commit shared preferences
 		for (SharedPreferences prefs : clear) {
@@ -97,7 +100,7 @@ class AndroidAccountManager extends AccountManagerImpl
 			for (File child : children) {
 				String name = child.getName();
 				if (!name.equals("lib") && !name.equals("shared_prefs")) {
-					IoUtils.deleteFileOrDir(child);
+					deleteFileOrDir(child);
 				}
 			}
 		}

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

@@ -19,9 +19,7 @@ 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.BATTERY_STATUS_CHARGING;
-import static android.os.BatteryManager.BATTERY_STATUS_FULL;
-import static android.os.BatteryManager.EXTRA_STATUS;
+import static android.os.BatteryManager.EXTRA_PLUGGED;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Logger.getLogger;
 
@@ -48,9 +46,8 @@ class AndroidBatteryManager implements BatteryManager, Service {
 		IntentFilter filter = new IntentFilter(ACTION_BATTERY_CHANGED);
 		Intent i = appContext.registerReceiver(null, filter);
 		if (i == null) return false;
-		int status = i.getIntExtra(EXTRA_STATUS, -1);
-		return status == BATTERY_STATUS_CHARGING ||
-				status == BATTERY_STATUS_FULL;
+		int status = i.getIntExtra(EXTRA_PLUGGED, 0);
+		return status != 0;
 	}
 
 	@Override

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

@@ -3,6 +3,7 @@ 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;
@@ -11,6 +12,11 @@ import dagger.Provides;
 @Module
 public class AndroidBatteryModule {
 
+	public static class EagerSingletons {
+		@Inject
+		BatteryManager batteryManager;
+	}
+
 	@Provides
 	@Singleton
 	BatteryManager provideBatteryManager(LifecycleManager lifecycleManager,

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

@@ -13,8 +13,7 @@ import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.network.NetworkStatus;
 import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
-import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Scheduler;
 
 import java.util.concurrent.Future;
@@ -34,16 +33,17 @@ import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.TYPE_WIFI;
 import static android.os.Build.VERSION.SDK_INT;
 import static android.os.PowerManager.ACTION_DEVICE_IDLE_MODE_CHANGED;
+import static java.util.Objects.requireNonNull;
 import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AndroidNetworkManager implements NetworkManager, Service {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidNetworkManager.class.getName());
+			getLogger(AndroidNetworkManager.class.getName());
 
 	// See android.net.wifi.WifiManager
 	private static final String WIFI_AP_STATE_CHANGED_ACTION =
@@ -56,6 +56,7 @@ class AndroidNetworkManager implements NetworkManager, Service {
 			new AtomicReference<>();
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
+	@Nullable
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	@Inject
@@ -89,9 +90,8 @@ class AndroidNetworkManager implements NetworkManager, Service {
 
 	@Override
 	public NetworkStatus getNetworkStatus() {
-		ConnectivityManager cm = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (cm == null) throw new AssertionError();
+		ConnectivityManager cm = (ConnectivityManager) requireNonNull(
+				appContext.getSystemService(CONNECTIVITY_SERVICE));
 		NetworkInfo net = cm.getActiveNetworkInfo();
 		boolean connected = net != null && net.isConnected();
 		boolean wifi = connected && net.getType() == TYPE_WIFI;

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

@@ -18,13 +18,12 @@ 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;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.BlockingQueue;
@@ -48,10 +47,11 @@ import static android.bluetooth.BluetoothAdapter.STATE_OFF;
 import static android.bluetooth.BluetoothAdapter.STATE_ON;
 import static android.bluetooth.BluetoothDevice.ACTION_FOUND;
 import static android.bluetooth.BluetoothDevice.EXTRA_DEVICE;
+import static java.util.Collections.shuffle;
 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 java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
@@ -59,7 +59,7 @@ import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidBluetoothPlugin.class.getName());
+			getLogger(AndroidBluetoothPlugin.class.getName());
 
 	private static final int MAX_DISCOVERY_MS = 10_000;
 
@@ -161,11 +161,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	@Override
 	void tryToClose(@Nullable BluetoothServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
 	}
 
 	@Override
@@ -195,7 +191,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 			s.connect();
 			return wrapSocket(s);
 		} catch (IOException e) {
-			tryToClose(s);
+			IoUtils.tryToClose(s, LOG, WARNING);
 			throw e;
 		}
 	}
@@ -264,18 +260,10 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 			appContext.unregisterReceiver(receiver);
 		}
 		// Shuffle the addresses so we don't always try the same one first
-		Collections.shuffle(addresses);
+		shuffle(addresses);
 		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/tcp/AndroidLanTcpPlugin.java

@@ -32,17 +32,19 @@ import static android.net.ConnectivityManager.TYPE_WIFI;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Logger.getLogger;
 
 @NotNullByDefault
 class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 
+	private static final Logger LOG =
+			getLogger(AndroidLanTcpPlugin.class.getName());
+
 	private static final byte[] WIFI_AP_ADDRESS_BYTES =
 			{(byte) 192, (byte) 168, 43, 1};
 	private static final InetAddress WIFI_AP_ADDRESS;
 
-	private static final Logger LOG =
-			Logger.getLogger(AndroidLanTcpPlugin.class.getName());
-
 	static {
 		try {
 			WIFI_AP_ADDRESS = InetAddress.getByAddress(WIFI_AP_ADDRESS_BYTES);
@@ -66,10 +68,8 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 		// Don't execute more than one connection status check at a time
 		connectionStatusExecutor =
 				new PoliteExecutor("AndroidLanTcpPlugin", ioExecutor, 1);
-		ConnectivityManager connectivityManager = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (connectivityManager == null) throw new AssertionError();
-		this.connectivityManager = connectivityManager;
+		connectivityManager = (ConnectivityManager) requireNonNull(
+				appContext.getSystemService(CONNECTIVITY_SERVICE));
 		wifiManager = (WifiManager) appContext.getApplicationContext()
 				.getSystemService(WIFI_SERVICE);
 		socketFactory = SocketFactory.getDefault();

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

@@ -8,8 +8,7 @@ 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;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.system.Clock;
@@ -26,10 +25,10 @@ import javax.net.SocketFactory;
 import static android.content.Context.MODE_PRIVATE;
 import static android.content.Context.POWER_SERVICE;
 import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
+import static java.util.Objects.requireNonNull;
 import static java.util.concurrent.TimeUnit.MINUTES;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AndroidTorPlugin extends TorPlugin {
 
 	// This tag may prevent Huawei's power manager from killing us
@@ -52,8 +51,7 @@ class AndroidTorPlugin extends TorPlugin {
 				appContext.getDir("tor", MODE_PRIVATE));
 		this.appContext = appContext;
 		PowerManager pm = (PowerManager)
-				appContext.getSystemService(POWER_SERVICE);
-		if (pm == null) throw new AssertionError();
+				requireNonNull(appContext.getSystemService(POWER_SERVICE));
 		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

@@ -1,7 +1,6 @@
 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;
@@ -26,12 +25,15 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.Immutable;
 import javax.net.SocketFactory;
 
+import static android.os.Build.VERSION.SDK_INT;
+import static java.util.logging.Logger.getLogger;
+
 @Immutable
 @NotNullByDefault
 public class AndroidTorPluginFactory implements DuplexPluginFactory {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidTorPluginFactory.class.getName());
+			getLogger(AndroidTorPluginFactory.class.getName());
 
 	private static final int MAX_LATENCY = 30 * 1000; // 30 seconds
 	private static final int MAX_IDLE_TIME = 30 * 1000; // 30 seconds
@@ -102,7 +104,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 			return null;
 		}
 		// Use position-independent executable for SDK >= 16
-		if (Build.VERSION.SDK_INT >= 16) architecture += "_pie";
+		if (SDK_INT >= 16) architecture += "_pie";
 
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);

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

@@ -15,12 +15,13 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static android.content.Context.TELEPHONY_SERVICE;
+import static java.util.logging.Logger.getLogger;
 
 @NotNullByDefault
 class AndroidLocationUtils implements LocationUtils {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidLocationUtils.class.getName());
+			getLogger(AndroidLocationUtils.class.getName());
 
 	private final Context appContext;
 
@@ -59,14 +60,14 @@ class AndroidLocationUtils implements LocationUtils {
 	}
 
 	private String getCountryFromPhoneNetwork() {
-		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
-		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getNetworkCountryIso();
+		TelephonyManager tm = (TelephonyManager)
+				appContext.getSystemService(TELEPHONY_SERVICE);
+		return tm == null ? "" : tm.getNetworkCountryIso();
 	}
 
 	private String getCountryFromSimCard() {
-		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
-		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getSimCountryIso();
+		TelephonyManager tm = (TelephonyManager)
+				appContext.getSystemService(TELEPHONY_SERVICE);
+		return tm == null ? "" : tm.getSimCountryIso();
 	}
 }

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;
@@ -7,7 +8,6 @@ import android.content.ContentResolver;
 import android.content.Context;
 import android.net.wifi.WifiConfiguration;
 import android.net.wifi.WifiManager;
-import android.os.Build;
 import android.os.Parcel;
 import android.os.StrictMode;
 import android.provider.Settings;
@@ -22,11 +22,14 @@ import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static android.content.Context.WIFI_SERVICE;
+import static android.os.Build.FINGERPRINT;
+import static android.os.Build.SERIAL;
+import static android.os.Build.VERSION.SDK_INT;
 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;
 
@@ -37,24 +40,27 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		appContext = app.getApplicationContext();
 	}
 
+	@SuppressLint("HardwareIds")
 	@Override
 	protected void writeToEntropyPool(DataOutputStream out) throws IOException {
 		super.writeToEntropyPool(out);
 		out.writeInt(android.os.Process.myPid());
 		out.writeInt(android.os.Process.myTid());
 		out.writeInt(android.os.Process.myUid());
-		if (Build.FINGERPRINT != null) out.writeUTF(Build.FINGERPRINT);
-		if (Build.SERIAL != null) out.writeUTF(Build.SERIAL);
+		if (FINGERPRINT != null) out.writeUTF(FINGERPRINT);
+		if (SERIAL != null) out.writeUTF(SERIAL);
 		ContentResolver contentResolver = appContext.getContentResolver();
 		String id = Settings.Secure.getString(contentResolver, ANDROID_ID);
 		if (id != null) out.writeUTF(id);
 		Parcel parcel = Parcel.obtain();
-		WifiManager wm =
-				(WifiManager) appContext.getSystemService(WIFI_SERVICE);
-		List<WifiConfiguration> configs = wm.getConfiguredNetworks();
-		if (configs != null) {
-			for (WifiConfiguration config : configs)
-				parcel.writeParcelable(config, 0);
+		WifiManager wm = (WifiManager) appContext.getApplicationContext()
+				.getSystemService(WIFI_SERVICE);
+		if (wm != null) {
+			List<WifiConfiguration> configs = wm.getConfiguredNetworks();
+			if (configs != null) {
+				for (WifiConfiguration config : configs)
+					parcel.writeParcelable(config, 0);
+			}
 		}
 		BluetoothAdapter bt = BluetoothAdapter.getDefaultAdapter();
 		if (bt != null) {
@@ -70,20 +76,18 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		// Silence strict mode
 		StrictMode.ThreadPolicy tp = StrictMode.allowThreadDiskWrites();
 		super.writeSeed();
-		if (Build.VERSION.SDK_INT >= 16 && Build.VERSION.SDK_INT <= 18)
-			applyOpenSslFix();
+		if (SDK_INT >= 16 && SDK_INT <= 18) applyOpenSslFix();
 		StrictMode.setThreadPolicy(tp);
 	}
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
 	private void applyOpenSslFix() {
-		byte[] seed = new LinuxSecureRandomSpi().engineGenerateSeed(
-				SEED_LENGTH);
+		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

@@ -3,17 +3,20 @@ package org.briarproject.bramble.util;
 import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothAdapter;
 import android.content.Context;
-import android.os.Build;
 import android.provider.Settings;
 
 import java.io.File;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 
 import static android.content.Context.MODE_PRIVATE;
+import static android.os.Build.CPU_ABI;
+import static android.os.Build.CPU_ABI2;
+import static android.os.Build.SUPPORTED_ABIS;
 import static android.os.Build.VERSION.SDK_INT;
+import static java.util.Arrays.asList;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 public class AndroidUtils {
 
@@ -22,14 +25,13 @@ public class AndroidUtils {
 
 	private static final String STORED_REPORTS = "dev-reports";
 
-	@SuppressWarnings("deprecation")
 	public static Collection<String> getSupportedArchitectures() {
 		List<String> abis = new ArrayList<>();
 		if (SDK_INT >= 21) {
-			abis.addAll(Arrays.asList(Build.SUPPORTED_ABIS));
+			abis.addAll(asList(SUPPORTED_ABIS));
 		} else {
-			abis.add(Build.CPU_ABI);
-			if (Build.CPU_ABI2 != null) abis.add(Build.CPU_ABI2);
+			abis.add(CPU_ABI);
+			if (CPU_ABI2 != null) abis.add(CPU_ABI2);
 		}
 		return abis;
 	}
@@ -49,7 +51,7 @@ public class AndroidUtils {
 	}
 
 	private static boolean isValidBluetoothAddress(String address) {
-		return !StringUtils.isNullOrEmpty(address)
+		return !isNullOrEmpty(address)
 				&& BluetoothAdapter.checkBluetoothAddress(address)
 				&& !address.equals(FAKE_BLUETOOTH_ADDRESS);
 	}

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

@@ -10,17 +10,19 @@ import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
 @ThreadSafe
 @NotNullByDefault
 public class RenewableWakeLock {
 
 	private static final Logger LOG =
-			Logger.getLogger(RenewableWakeLock.class.getName());
+			getLogger(RenewableWakeLock.class.getName());
 
 	/**
 	 * Automatically release the lock this many milliseconds after it's due
@@ -36,10 +38,12 @@ public class RenewableWakeLock {
 	private final Runnable renewTask;
 
 	private final Object lock = new Object();
+	@GuardedBy("lock")
 	@Nullable
-	private PowerManager.WakeLock wakeLock; // Locking: lock
+	private PowerManager.WakeLock wakeLock;
+	@GuardedBy("lock")
 	@Nullable
-	private ScheduledFuture future; // Locking: lock
+	private ScheduledFuture future;
 
 	public RenewableWakeLock(PowerManager powerManager,
 			ScheduledExecutorService scheduler, int levelAndFlags, String tag,

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

@@ -1,13 +1,14 @@
 package org.briarproject.bramble.api;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.util.Arrays;
 import java.util.Comparator;
 
 import javax.annotation.concurrent.ThreadSafe;
 
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 /**
  * A wrapper around a byte array, to allow it to be stored in maps etc.
  */
@@ -56,8 +57,7 @@ public class Bytes implements Comparable<Bytes> {
 
 	@Override
 	public String toString() {
-		return getClass().getSimpleName() +
-				"(" + StringUtils.toHexString(getBytes()) + ")";
+		return getClass().getSimpleName() + "(" + toHexString(getBytes()) + ")";
 	}
 
 	public static class BytesComparator implements Comparator<Bytes> {

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

@@ -2,7 +2,6 @@ package org.briarproject.bramble.api;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -10,6 +9,8 @@ import java.util.Set;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Collections.unmodifiableSet;
+
 @NotThreadSafe
 @NotNullByDefault
 public class Multiset<T> {
@@ -96,6 +97,6 @@ public class Multiset<T> {
 	 * is unmodifiable.
 	 */
 	public Set<T> keySet() {
-		return Collections.unmodifiableSet(map.keySet());
+		return unmodifiableSet(map.keySet());
 	}
 }

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/BdfMessageContext.java

@@ -5,10 +5,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
 
 import java.util.Collection;
-import java.util.Collections;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public class BdfMessageContext {
@@ -23,7 +24,7 @@ public class BdfMessageContext {
 	}
 
 	public BdfMessageContext(BdfDictionary dictionary) {
-		this(dictionary, Collections.emptyList());
+		this(dictionary, emptyList());
 	}
 
 	public BdfDictionary getDictionary() {

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

@@ -9,13 +9,14 @@ 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;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOCK_DIFFERENCE;
 
 @Immutable
@@ -23,7 +24,7 @@ import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOC
 public abstract class BdfMessageValidator implements MessageValidator {
 
 	protected static final Logger LOG =
-			Logger.getLogger(BdfMessageValidator.class.getName());
+			getLogger(BdfMessageValidator.class.getName());
 
 	protected final ClientHelper clientHelper;
 	protected final MetadataEncoder metadataEncoder;

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.
 	 */

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/BdfDictionary.java

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
 
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.TreeMap;
 
 import javax.annotation.Nullable;
@@ -24,9 +23,9 @@ public class BdfDictionary extends TreeMap<String, Object> {
 	 * );
 	 * </pre>
 	 */
-	public static BdfDictionary of(Entry<String, ?>... entries) {
+	public static BdfDictionary of(BdfEntry... entries) {
 		BdfDictionary d = new BdfDictionary();
-		for (Entry<String, ?> e : entries) d.put(e.getKey(), e.getValue());
+		for (BdfEntry e : entries) d.put(e.getKey(), e.getValue());
 		return d;
 	}
 

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

@@ -4,12 +4,12 @@ import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.api.FormatException;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Arrays.asList;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
 
 @NotThreadSafe
@@ -22,7 +22,7 @@ public class BdfList extends ArrayList<Object> {
 	 * </pre>
 	 */
 	public static BdfList of(Object... items) {
-		return new BdfList(Arrays.asList(items));
+		return new BdfList(asList(items));
 	}
 
 	public BdfList() {
@@ -33,6 +33,7 @@ public class BdfList extends ArrayList<Object> {
 		super(items);
 	}
 
+	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 	private boolean isInRange(int index) {
 		return index >= 0 && index < size();
 	}

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.
@@ -374,12 +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)
-			throws DbException;
+	Map<MessageId, MessageState> getMessageDependencies(Transaction txn,
+			MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs and states of all dependents of the given message.
@@ -388,15 +387,16 @@ public interface DatabaseComponent {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependents(Transaction txn, MessageId m)
-			throws DbException;
+	Map<MessageId, MessageState> getMessageDependents(Transaction txn,
+			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
@@ -543,7 +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/Transaction.java

@@ -3,11 +3,12 @@ package org.briarproject.bramble.api.db;
 import org.briarproject.bramble.api.event.Event;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Collections.emptyList;
+
 /**
  * A wrapper around a database transaction. Transactions are not thread-safe.
  */
@@ -53,7 +54,7 @@ public class Transaction {
 	 * Returns any events attached to the transaction.
 	 */
 	public List<Event> getEvents() {
-		if (events == null) return Collections.emptyList();
+		if (events == null) return emptyList();
 		return events;
 	}
 

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

@@ -2,12 +2,12 @@ package org.briarproject.bramble.api.identity;
 
 import org.briarproject.bramble.api.Nameable;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 /**
  * A pseudonym for a user.
@@ -28,7 +28,7 @@ public class Author implements Nameable {
 
 	public Author(AuthorId id, int formatVersion, String name,
 			byte[] publicKey) {
-		int nameLength = StringUtils.toUtf8(name).length;
+		int nameLength = toUtf8(name).length;
 		if (nameLength == 0 || nameLength > MAX_AUTHOR_NAME_LENGTH)
 			throw new IllegalArgumentException();
 		if (publicKey.length == 0 || publicKey.length > MAX_PUBLIC_KEY_LENGTH)

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/plugin/TransportId.java

@@ -1,6 +1,6 @@
 package org.briarproject.bramble.api.plugin;
 
-import org.briarproject.bramble.util.StringUtils;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 /**
  * Type-safe wrapper for a namespaced string that uniquely identifies a
@@ -11,12 +11,12 @@ public class TransportId {
 	/**
 	 * The maximum length of a transport identifier in UTF-8 bytes.
 	 */
-	public static int MAX_TRANSPORT_ID_LENGTH = 100;
+	public static final int MAX_TRANSPORT_ID_LENGTH = 100;
 
 	private final String id;
 
 	public TransportId(String id) {
-		int length = StringUtils.toUtf8(id).length;
+		int length = toUtf8(id).length;
 		if (length == 0 || length > MAX_TRANSPORT_ID_LENGTH)
 			throw new IllegalArgumentException();
 		this.id = id;

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

@@ -1,10 +1,11 @@
 package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
+
 /**
  * Type-safe wrapper for a namespaced string that uniquely identifies a sync
  * client.
@@ -16,12 +17,12 @@ public class ClientId implements Comparable<ClientId> {
 	/**
 	 * The maximum length of a client identifier in UTF-8 bytes.
 	 */
-	public static int MAX_CLIENT_ID_LENGTH = 100;
+	public static final int MAX_CLIENT_ID_LENGTH = 100;
 
 	private final String id;
 
 	public ClientId(String id) {
-		int length = StringUtils.toUtf8(id).length;
+		int length = toUtf8(id).length;
 		if (length == 0 || length > MAX_CLIENT_ID_LENGTH)
 			throw new IllegalArgumentException();
 		this.id = id;

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

@@ -4,10 +4,11 @@ import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.util.Collection;
-import java.util.Collections;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public class MessageContext {
@@ -22,7 +23,7 @@ public class MessageContext {
 	}
 
 	public MessageContext(Metadata metadata) {
-		this(metadata, Collections.emptyList());
+		this(metadata, emptyList());
 	}
 
 	public Metadata getMetadata() {

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

@@ -8,17 +8,21 @@ 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 java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
 public class IoUtils {
 
-	private static final Logger LOG = Logger.getLogger(IoUtils.class.getName());
+	private static final Logger LOG = getLogger(IoUtils.class.getName());
 
 	public static void deleteFileOrDir(File f) {
 		if (f.isFile()) {
@@ -54,16 +58,35 @@ public class IoUtils {
 			out.flush();
 			out.close();
 		} catch (IOException e) {
-			tryToClose(in);
-			tryToClose(out);
+			tryToClose(in, LOG, WARNING);
+			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/ValidationUtils.java

@@ -7,13 +7,15 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import javax.annotation.Nullable;
 
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
+
 @NotNullByDefault
 public class ValidationUtils {
 
 	public static void checkLength(@Nullable String s, int minLength,
 			int maxLength) throws FormatException {
 		if (s != null) {
-			int length = StringUtils.toUtf8(s).length;
+			int length = toUtf8(s).length;
 			if (length < minLength) throw new FormatException();
 			if (length > maxLength) throw new FormatException();
 		}
@@ -21,7 +23,7 @@ public class ValidationUtils {
 
 	public static void checkLength(@Nullable String s, int length)
 			throws FormatException {
-		if (s != null && StringUtils.toUtf8(s).length != length)
+		if (s != null && toUtf8(s).length != length)
 			throw new FormatException();
 	}
 

bramble-api/src/test/java/org/briarproject/bramble/api/data/BdfDictionaryTest.java

@@ -8,6 +8,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.Map.Entry;
 
+import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
@@ -19,15 +20,15 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	public void testConstructors() {
 		assertEquals(Collections.<String, Object>emptyMap(),
 				new BdfDictionary());
-		assertEquals(Collections.singletonMap("foo", NULL_VALUE),
-				new BdfDictionary(Collections.singletonMap("foo", NULL_VALUE)));
+		assertEquals(singletonMap("foo", NULL_VALUE),
+				new BdfDictionary(singletonMap("foo", NULL_VALUE)));
 	}
 
 	@Test
 	public void testFactoryMethod() {
 		assertEquals(Collections.<String, Object>emptyMap(),
 				BdfDictionary.of());
-		assertEquals(Collections.singletonMap("foo", NULL_VALUE),
+		assertEquals(singletonMap("foo", NULL_VALUE),
 				BdfDictionary.of(new BdfEntry("foo", NULL_VALUE)));
 	}
 
@@ -67,7 +68,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testKeySetIteratorIsOrderedByKeys() throws Exception {
+	public void testKeySetIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);
@@ -86,7 +87,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testValuesIteratorIsOrderedByKeys() throws Exception {
+	public void testValuesIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);
@@ -105,7 +106,7 @@ public class BdfDictionaryTest extends BrambleTestCase {
 	}
 
 	@Test
-	public void testEntrySetIteratorIsOrderedByKeys() throws Exception {
+	public void testEntrySetIteratorIsOrderedByKeys() {
 		BdfDictionary d = new BdfDictionary();
 		d.put("a", 1);
 		d.put("d", 4);

bramble-api/src/test/java/org/briarproject/bramble/api/data/BdfListTest.java

@@ -5,26 +5,31 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.junit.Test;
 
-import java.util.Arrays;
-import java.util.Collections;
+import java.util.Random;
 
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
 import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
+import static org.briarproject.bramble.util.StringUtils.getRandomString;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 
 public class BdfListTest extends BrambleTestCase {
 
+	private final Random random = new Random();
+
 	@Test
 	public void testConstructors() {
-		assertEquals(Collections.emptyList(), new BdfList());
-		assertEquals(Arrays.asList(1, 2, NULL_VALUE),
-				new BdfList(Arrays.asList(1, 2, NULL_VALUE)));
+		assertEquals(emptyList(), new BdfList());
+		assertEquals(asList(1, 2, NULL_VALUE),
+				new BdfList(asList(1, 2, NULL_VALUE)));
 	}
 
 	@Test
 	public void testFactoryMethod() {
-		assertEquals(Collections.emptyList(), BdfList.of());
-		assertEquals(Arrays.asList(1, 2, NULL_VALUE),
+		assertEquals(emptyList(), BdfList.of());
+		assertEquals(asList(1, 2, NULL_VALUE),
 				BdfList.of(1, 2, NULL_VALUE));
 	}
 
@@ -64,22 +69,21 @@ public class BdfListTest extends BrambleTestCase {
 	}
 
 	@Test
-	@SuppressWarnings("ConstantConditions")
-	public void testIndexOutOfBoundsReturnsDefaultValue() throws Exception {
+	public void testIndexOutOfBoundsReturnsDefaultValue() {
 		BdfList list = BdfList.of(1, 2, 3);
-		boolean defaultBoolean = true;
+		boolean defaultBoolean = random.nextBoolean();
 		assertEquals(defaultBoolean, list.getBoolean(-1, defaultBoolean));
 		assertEquals(defaultBoolean, list.getBoolean(3, defaultBoolean));
-		Long defaultLong = 123L;
+		Long defaultLong = random.nextLong();
 		assertEquals(defaultLong, list.getLong(-1, defaultLong));
 		assertEquals(defaultLong, list.getLong(3, defaultLong));
-		Double defaultDouble = 1.23;
+		Double defaultDouble = random.nextDouble();
 		assertEquals(defaultDouble, list.getDouble(-1, defaultDouble));
 		assertEquals(defaultDouble, list.getDouble(3, defaultDouble));
-		String defaultString = "123";
+		String defaultString = getRandomString(123);
 		assertEquals(defaultString, list.getString(-1, defaultString));
 		assertEquals(defaultString, list.getString(3, defaultString));
-		byte[] defaultBytes = new byte[] {1, 2, 3};
+		byte[] defaultBytes = getRandomBytes(123);
 		assertArrayEquals(defaultBytes, list.getRaw(-1, defaultBytes));
 		assertArrayEquals(defaultBytes, list.getRaw(3, defaultBytes));
 		BdfList defaultList = BdfList.of(1, 2, 3);
@@ -95,18 +99,17 @@ public class BdfListTest extends BrambleTestCase {
 	}
 
 	@Test
-	@SuppressWarnings("ConstantConditions")
-	public void testWrongTypeReturnsDefaultValue() throws Exception {
+	public void testWrongTypeReturnsDefaultValue() {
 		BdfList list = BdfList.of(1, 2, 3, true);
-		boolean defaultBoolean = true;
+		boolean defaultBoolean = random.nextBoolean();
 		assertEquals(defaultBoolean, list.getBoolean(0, defaultBoolean));
-		Long defaultLong = 123L;
+		Long defaultLong = random.nextLong();
 		assertEquals(defaultLong, list.getLong(3, defaultLong));
-		Double defaultDouble = 1.23;
+		Double defaultDouble = random.nextDouble();
 		assertEquals(defaultDouble, list.getDouble(0, defaultDouble));
-		String defaultString = "123";
+		String defaultString = getRandomString(123);
 		assertEquals(defaultString, list.getString(0, defaultString));
-		byte[] defaultBytes = new byte[] {1, 2, 3};
+		byte[] defaultBytes = getRandomBytes(123);
 		assertArrayEquals(defaultBytes, list.getRaw(0, defaultBytes));
 		BdfList defaultList = BdfList.of(1, 2, 3);
 		assertEquals(defaultList, list.getList(0, defaultList));

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

@@ -12,12 +12,10 @@ 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.util.IoUtils;
 
 import java.io.File;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -25,6 +23,7 @@ import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.util.Arrays.asList;
+import static java.util.Collections.sort;
 import static org.briarproject.bramble.api.identity.Author.FORMAT_VERSION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
@@ -33,6 +32,7 @@ import static org.briarproject.bramble.api.properties.TransportPropertyConstants
 import static org.briarproject.bramble.api.sync.ClientId.MAX_CLIENT_ID_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_GROUP_DESCRIPTOR_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
 import static org.briarproject.bramble.util.StringUtils.getRandomString;
 
 public class TestUtils {
@@ -48,8 +48,10 @@ public class TestUtils {
 	}
 
 	public static void deleteTestDirectory(File testDir) {
-		IoUtils.deleteFileOrDir(testDir);
-		testDir.getParentFile().delete(); // Delete if empty
+		deleteFileOrDir(testDir);
+		// Delete parent directory only if it's empty
+		//noinspection ResultOfMethodCallIgnored
+		testDir.getParentFile().delete();
 	}
 
 	public static byte[] getRandomBytes(int length) {
@@ -145,7 +147,7 @@ public class TestUtils {
 		if (size == 0) throw new IllegalArgumentException();
 		List<Double> sorted = new ArrayList<>(size);
 		for (Number n : samples) sorted.add(n.doubleValue());
-		Collections.sort(sorted);
+		sort(sorted);
 		if (size % 2 == 1) return sorted.get(size / 2);
 		double low = sorted.get(size / 2 - 1), high = sorted.get(size / 2);
 		return (low + high) / 2;

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/PoliteExecutor.java

@@ -10,6 +10,7 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.GuardedBy;
 
 import static java.util.logging.Level.FINE;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.now;
 
 /**
@@ -42,7 +43,7 @@ public class PoliteExecutor implements Executor {
 			int maxConcurrentTasks) {
 		this.delegate = delegate;
 		this.maxConcurrentTasks = maxConcurrentTasks;
-		log = Logger.getLogger(tag);
+		log = getLogger(tag);
 	}
 
 	@Override

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

@@ -9,6 +9,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.FINE;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.now;
 
 @NotNullByDefault
@@ -22,7 +23,7 @@ public class TimeLoggingExecutor extends ThreadPoolExecutor {
 			RejectedExecutionHandler handler) {
 		super(corePoolSize, maxPoolSize, keepAliveTime, unit, workQueue,
 				handler);
-		log = Logger.getLogger(tag);
+		log = getLogger(tag);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/account/AccountManagerImpl.java

@@ -6,9 +6,7 @@ import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.identity.LocalAuthor;
-import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.util.IoUtils;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.BufferedReader;
 import java.io.File;
@@ -19,19 +17,21 @@ import java.io.InputStreamReader;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.fromHexString;
 import static org.briarproject.bramble.util.StringUtils.toHexString;
 
-@MethodsNotNullByDefault
-@ParametersNotNullByDefault
+@NotNullByDefault
 class AccountManagerImpl implements AccountManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(AccountManagerImpl.class.getName());
+			getLogger(AccountManagerImpl.class.getName());
 
 	private static final String DB_KEY_FILENAME = "db.key";
 	private static final String DB_KEY_BACKUP_FILENAME = "db.key.bak";
@@ -68,7 +68,7 @@ class AccountManagerImpl implements AccountManager {
 		return databaseKey;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	protected String loadEncryptedDatabaseKey() {
 		String key = readDbKeyFromFile(dbKeyFile);
@@ -83,7 +83,7 @@ class AccountManagerImpl implements AccountManager {
 		return key;
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	private String readDbKeyFromFile(File f) {
 		if (!f.exists()) {
@@ -102,8 +102,8 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
-	protected boolean storeEncryptedDatabaseKey(String hex) {
+	@GuardedBy("stateChangeLock")
+	boolean storeEncryptedDatabaseKey(String hex) {
 		LOG.info("Storing database key in file");
 		// Create the directory if necessary
 		if (databaseConfig.getDatabaseKeyDirectory().mkdirs())
@@ -140,7 +140,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private void writeDbKeyToFile(String key, File f) throws IOException {
 		FileOutputStream out = new FileOutputStream(f);
 		out.write(key.getBytes("UTF-8"));
@@ -170,7 +170,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	private boolean encryptAndStoreDatabaseKey(SecretKey key, String password) {
 		byte[] plaintext = key.getBytes();
 		byte[] ciphertext = crypto.encryptWithPassword(plaintext, password);
@@ -181,8 +181,8 @@ class AccountManagerImpl implements AccountManager {
 	public void deleteAccount() {
 		synchronized (stateChangeLock) {
 			LOG.info("Deleting account");
-			IoUtils.deleteFileOrDir(databaseConfig.getDatabaseKeyDirectory());
-			IoUtils.deleteFileOrDir(databaseConfig.getDatabaseDirectory());
+			deleteFileOrDir(databaseConfig.getDatabaseKeyDirectory());
+			deleteFileOrDir(databaseConfig.getDatabaseDirectory());
 			databaseKey = null;
 		}
 	}
@@ -197,7 +197,7 @@ class AccountManagerImpl implements AccountManager {
 		}
 	}
 
-	// Locking: stateChangeLock
+	@GuardedBy("stateChangeLock")
 	@Nullable
 	private SecretKey loadAndDecryptDatabaseKey(String password) {
 		String hex = loadEncryptedDatabaseKey();

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

@@ -43,6 +43,7 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.contact.RecordTypes.CONTACT_INFO;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_SIGNATURE_LENGTH;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -54,7 +55,7 @@ import static org.briarproject.bramble.util.ValidationUtils.checkSize;
 class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 
 	private static final Logger LOG =
-			Logger.getLogger(ContactExchangeTaskImpl.class.getName());
+			getLogger(ContactExchangeTaskImpl.class.getName());
 
 	private static final String SIGNING_LABEL_EXCHANGE =
 			"org.briarproject.briar.contact/EXCHANGE";
@@ -190,6 +191,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			streamWriter.sendEndOfStream();
 			// Skip any remaining records from the incoming stream
 			try {
+				//noinspection InfiniteLoopStatement
 				while (true) recordReader.readRecord();
 			} catch (EOFException expected) {
 				LOG.info("End of stream");

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;
@@ -84,6 +96,48 @@ class ContactManagerImpl implements ContactManager {
 						verified, active));
 	}
 
+	@Override
+	public String getRemoteContactLink() {
+		// 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 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 {
 		return db.transactionWithResult(true, txn -> db.getContact(txn, c));

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

@@ -2,18 +2,20 @@ package org.briarproject.bramble.crypto;
 
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
+
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
 
 @NotNullByDefault
 class AsciiArmour {
 
 	static String wrap(byte[] b, int lineLength) {
-		String wrapped = StringUtils.toHexString(b);
+		String wrapped = toHexString(b);
 		StringBuilder s = new StringBuilder();
 		int length = wrapped.length();
 		for (int i = 0; i < length; i += lineLength) {
 			int end = Math.min(i + lineLength, length);
-			s.append(wrapped.substring(i, end));
+			s.append(wrapped, i, end);
 			s.append("\r\n");
 		}
 		return s.toString();
@@ -21,7 +23,7 @@ class AsciiArmour {
 
 	static byte[] unwrap(String s) throws FormatException {
 		try {
-			return StringUtils.fromHexString(s.replaceAll("[^0-9a-fA-F]", ""));
+			return fromHexString(s.replaceAll("[^0-9a-fA-F]", ""));
 		} catch (IllegalArgumentException e) {
 			throw new FormatException();
 		}

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

@@ -12,8 +12,6 @@ import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.SecureRandomProvider;
-import org.briarproject.bramble.util.ByteUtils;
-import org.briarproject.bramble.util.StringUtils;
 import org.spongycastle.crypto.CryptoException;
 import org.spongycastle.crypto.Digest;
 import org.spongycastle.crypto.digests.Blake2bDigest;
@@ -30,16 +28,21 @@ import java.util.logging.Logger;
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.lang.System.arraycopy;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.ByteUtils.INT_32_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.readUint32;
+import static org.briarproject.bramble.util.ByteUtils.writeUint32;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 @NotNullByDefault
 class CryptoComponentImpl implements CryptoComponent {
 
 	private static final Logger LOG =
-			Logger.getLogger(CryptoComponentImpl.class.getName());
+			getLogger(CryptoComponentImpl.class.getName());
 
 	private static final int SIGNATURE_KEY_PAIR_BITS = 256;
 	private static final int STORAGE_IV_BYTES = 24; // 196 bits
@@ -188,7 +191,7 @@ class CryptoComponentImpl implements CryptoComponent {
 		PrivateKey ourPriv = ourKeyPair.getPrivate();
 		byte[][] hashInputs = new byte[inputs.length + 1][];
 		hashInputs[0] = performRawKeyAgreement(ourPriv, theirPublicKey);
-		System.arraycopy(inputs, 0, hashInputs, 1, inputs.length);
+		arraycopy(inputs, 0, hashInputs, 1, inputs.length);
 		byte[] hash = hash(label, hashInputs);
 		if (hash.length != SecretKey.LENGTH) throw new IllegalStateException();
 		return new SecretKey(hash);
@@ -216,26 +219,26 @@ class CryptoComponentImpl implements CryptoComponent {
 
 	private void updateSignature(Signature signature, String label,
 			byte[] toSign) throws GeneralSecurityException {
-		byte[] labelBytes = StringUtils.toUtf8(label);
+		byte[] labelBytes = toUtf8(label);
 		byte[] length = new byte[INT_32_BYTES];
-		ByteUtils.writeUint32(labelBytes.length, length, 0);
+		writeUint32(labelBytes.length, length, 0);
 		signature.update(length);
 		signature.update(labelBytes);
-		ByteUtils.writeUint32(toSign.length, length, 0);
+		writeUint32(toSign.length, length, 0);
 		signature.update(length);
 		signature.update(toSign);
 	}
 
 	@Override
 	public byte[] hash(String label, byte[]... inputs) {
-		byte[] labelBytes = StringUtils.toUtf8(label);
+		byte[] labelBytes = toUtf8(label);
 		Digest digest = new Blake2bDigest(256);
 		byte[] length = new byte[INT_32_BYTES];
-		ByteUtils.writeUint32(labelBytes.length, length, 0);
+		writeUint32(labelBytes.length, length, 0);
 		digest.update(length, 0, length.length);
 		digest.update(labelBytes, 0, labelBytes.length);
 		for (byte[] input : inputs) {
-			ByteUtils.writeUint32(input.length, length, 0);
+			writeUint32(input.length, length, 0);
 			digest.update(length, 0, length.length);
 			digest.update(input, 0, input.length);
 		}
@@ -246,14 +249,14 @@ class CryptoComponentImpl implements CryptoComponent {
 
 	@Override
 	public byte[] mac(String label, SecretKey macKey, byte[]... inputs) {
-		byte[] labelBytes = StringUtils.toUtf8(label);
+		byte[] labelBytes = toUtf8(label);
 		Digest mac = new Blake2bDigest(macKey.getBytes(), 32, null, null);
 		byte[] length = new byte[INT_32_BYTES];
-		ByteUtils.writeUint32(labelBytes.length, length, 0);
+		writeUint32(labelBytes.length, length, 0);
 		mac.update(length, 0, length.length);
 		mac.update(labelBytes, 0, labelBytes.length);
 		for (byte[] input : inputs) {
-			ByteUtils.writeUint32(input.length, length, 0);
+			writeUint32(input.length, length, 0);
 			mac.update(length, 0, length.length);
 			mac.update(input, 0, input.length);
 		}
@@ -297,13 +300,13 @@ class CryptoComponentImpl implements CryptoComponent {
 		output[outputOff] = PBKDF_FORMAT_SCRYPT;
 		outputOff++;
 		// Salt
-		System.arraycopy(salt, 0, output, outputOff, salt.length);
+		arraycopy(salt, 0, output, outputOff, salt.length);
 		outputOff += salt.length;
 		// Cost parameter
-		ByteUtils.writeUint32(cost, output, outputOff);
+		writeUint32(cost, output, outputOff);
 		outputOff += INT_32_BYTES;
 		// IV
-		System.arraycopy(iv, 0, output, outputOff, iv.length);
+		arraycopy(iv, 0, output, outputOff, iv.length);
 		outputOff += iv.length;
 		// Initialise the cipher and encrypt the plaintext
 		try {
@@ -333,16 +336,16 @@ class CryptoComponentImpl implements CryptoComponent {
 			return null; // Unknown format
 		// Salt
 		byte[] salt = new byte[PBKDF_SALT_BYTES];
-		System.arraycopy(input, inputOff, salt, 0, salt.length);
+		arraycopy(input, inputOff, salt, 0, salt.length);
 		inputOff += salt.length;
 		// Cost parameter
-		long cost = ByteUtils.readUint32(input, inputOff);
+		long cost = readUint32(input, inputOff);
 		inputOff += INT_32_BYTES;
 		if (cost < 2 || cost > Integer.MAX_VALUE)
 			return null; // Invalid cost parameter
 		// IV
 		byte[] iv = new byte[STORAGE_IV_BYTES];
-		System.arraycopy(input, inputOff, iv, 0, iv.length);
+		arraycopy(input, inputOff, iv, 0, iv.length);
 		inputOff += iv.length;
 		// Derive the key from the password
 		SecretKey key = passwordBasedKdf.deriveKey(password, salt, (int) cost);

bramble-core/src/main/java/org/briarproject/bramble/crypto/Curve25519KeyParser.java

@@ -7,6 +7,8 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.security.GeneralSecurityException;
 
+import static java.lang.System.arraycopy;
+
 @NotNullByDefault
 class Curve25519KeyParser implements KeyParser {
 
@@ -26,7 +28,7 @@ class Curve25519KeyParser implements KeyParser {
 
 	static byte[] clamp(byte[] b) {
 		byte[] clamped = new byte[32];
-		System.arraycopy(b, 0, clamped, 0, 32);
+		arraycopy(b, 0, clamped, 0, 32);
 		clamped[0] &= 248;
 		clamped[31] &= 127;
 		clamped[31] |= 64;

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

@@ -1,13 +1,15 @@
 package org.briarproject.bramble.crypto;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.ByteUtils;
 
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_HEADER_PLAINTEXT_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_NONCE_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_PAYLOAD_LENGTH;
 import static org.briarproject.bramble.util.ByteUtils.INT_16_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.readUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint64;
 
 @NotNullByDefault
 class FrameEncoder {
@@ -16,7 +18,7 @@ class FrameEncoder {
 		if (dest.length < FRAME_NONCE_LENGTH)
 			throw new IllegalArgumentException();
 		if (frameNumber < 0) throw new IllegalArgumentException();
-		ByteUtils.writeUint64(frameNumber, dest, 0);
+		writeUint64(frameNumber, dest, 0);
 		if (header) dest[0] |= 0x80;
 		for (int i = INT_64_BYTES; i < FRAME_NONCE_LENGTH; i++) dest[i] = 0;
 	}
@@ -29,8 +31,8 @@ class FrameEncoder {
 		if (paddingLength < 0) throw new IllegalArgumentException();
 		if (payloadLength + paddingLength > MAX_PAYLOAD_LENGTH)
 			throw new IllegalArgumentException();
-		ByteUtils.writeUint16(payloadLength, dest, 0);
-		ByteUtils.writeUint16(paddingLength, dest, INT_16_BYTES);
+		writeUint16(payloadLength, dest, 0);
+		writeUint16(paddingLength, dest, INT_16_BYTES);
 		if (finalFrame) dest[0] |= 0x80;
 	}
 
@@ -43,12 +45,12 @@ class FrameEncoder {
 	static int getPayloadLength(byte[] header) {
 		if (header.length < FRAME_HEADER_PLAINTEXT_LENGTH)
 			throw new IllegalArgumentException();
-		return ByteUtils.readUint16(header, 0) & 0x7FFF;
+		return readUint16(header, 0) & 0x7FFF;
 	}
 
 	static int getPaddingLength(byte[] header) {
 		if (header.length < FRAME_HEADER_PLAINTEXT_LENGTH)
 			throw new IllegalArgumentException();
-		return ByteUtils.readUint16(header, INT_16_BYTES);
+		return readUint16(header, INT_16_BYTES);
 	}
 }

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

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.crypto.SecretKey;
 
 import javax.inject.Inject;
 
+import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
 
 class KeyAgreementCryptoImpl implements KeyAgreementCrypto {
@@ -24,7 +25,7 @@ class KeyAgreementCryptoImpl implements KeyAgreementCrypto {
 		byte[] hash = crypto.hash(COMMIT_LABEL, publicKey.getEncoded());
 		// The output is the first COMMIT_LENGTH bytes of the hash
 		byte[] commitment = new byte[COMMIT_LENGTH];
-		System.arraycopy(hash, 0, commitment, 0, COMMIT_LENGTH);
+		arraycopy(hash, 0, commitment, 0, COMMIT_LENGTH);
 		return commitment;
 	}
 

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

@@ -5,7 +5,6 @@ import org.briarproject.bramble.api.crypto.KeyParser;
 import org.briarproject.bramble.api.crypto.PrivateKey;
 import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.StringUtils;
 import org.spongycastle.asn1.teletrust.TeleTrusTNamedCurves;
 import org.spongycastle.asn1.x9.X9ECParameters;
 import org.spongycastle.crypto.AsymmetricCipherKeyPair;
@@ -45,6 +44,9 @@ import java.util.Scanner;
 
 import javax.annotation.concurrent.Immutable;
 
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 @Immutable
 @NotNullByDefault
 public class MessageEncrypter {
@@ -157,6 +159,7 @@ public class MessageEncrypter {
 			printUsage();
 			System.exit(1);
 		}
+		//noinspection IfCanBeSwitch
 		if (args[0].equals("generate")) {
 			if (args.length != 3) {
 				printUsage();
@@ -210,11 +213,11 @@ public class MessageEncrypter {
 		MessageEncrypter encrypter = new MessageEncrypter(random);
 		KeyPair keyPair = encrypter.generateKeyPair();
 		PrintStream out = new PrintStream(new FileOutputStream(publicKeyFile));
-		out.print(StringUtils.toHexString(keyPair.getPublic().getEncoded()));
+		out.print(toHexString(keyPair.getPublic().getEncoded()));
 		out.flush();
 		out.close();
 		out = new PrintStream(new FileOutputStream(privateKeyFile));
-		out.print(StringUtils.toHexString(keyPair.getPrivate().getEncoded()));
+		out.print(toHexString(keyPair.getPrivate().getEncoded()));
 		out.flush();
 		out.close();
 	}
@@ -223,7 +226,7 @@ public class MessageEncrypter {
 		SecureRandom random = new SecureRandom();
 		MessageEncrypter encrypter = new MessageEncrypter(random);
 		InputStream in = new FileInputStream(publicKeyFile);
-		byte[] keyBytes = StringUtils.fromHexString(readFully(in).trim());
+		byte[] keyBytes = fromHexString(readFully(in).trim());
 		PublicKey publicKey =
 				encrypter.getKeyParser().parsePublicKey(keyBytes);
 		String message = readFully(System.in);
@@ -236,7 +239,7 @@ public class MessageEncrypter {
 		SecureRandom random = new SecureRandom();
 		MessageEncrypter encrypter = new MessageEncrypter(random);
 		InputStream in = new FileInputStream(privateKeyFile);
-		byte[] keyBytes = StringUtils.fromHexString(readFully(in).trim());
+		byte[] keyBytes = fromHexString(readFully(in).trim());
 		PrivateKey privateKey =
 				encrypter.getKeyParser().parsePrivateKey(keyBytes);
 		byte[] ciphertext = AsciiArmour.unwrap(readFully(System.in));

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

@@ -2,7 +2,6 @@ package org.briarproject.bramble.crypto;
 
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.util.StringUtils;
 import org.spongycastle.crypto.generators.SCrypt;
 
 import java.util.logging.Logger;
@@ -10,13 +9,14 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 class ScryptKdf implements PasswordBasedKdf {
 
-	private static final Logger LOG =
-			Logger.getLogger(ScryptKdf.class.getName());
+	private static final Logger LOG = getLogger(ScryptKdf.class.getName());
 
 	private static final int MIN_COST = 256; // Min parameter N
 	private static final int MAX_COST = 1024 * 1024; // Max parameter N
@@ -53,7 +53,7 @@ class ScryptKdf implements PasswordBasedKdf {
 	@Override
 	public SecretKey deriveKey(String password, byte[] salt, int cost) {
 		long start = now();
-		byte[] passwordBytes = StringUtils.toUtf8(password);
+		byte[] passwordBytes = toUtf8(password);
 		SecretKey k = new SecretKey(SCrypt.generate(passwordBytes, salt, cost,
 				BLOCK_SIZE, PARALLELIZATION, SecretKey.LENGTH));
 		logDuration(LOG, "Deriving key from password", start);

bramble-core/src/main/java/org/briarproject/bramble/crypto/Sec1KeyParser.java

@@ -16,6 +16,8 @@ import java.util.logging.Logger;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.lang.System.arraycopy;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
 
@@ -28,8 +30,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 @NotNullByDefault
 class Sec1KeyParser implements KeyParser {
 
-	private static final Logger LOG =
-			Logger.getLogger(Sec1KeyParser.class.getName());
+	private static final Logger LOG = getLogger(Sec1KeyParser.class.getName());
 
 	private final ECDomainParameters params;
 	private final BigInteger modulus;
@@ -56,12 +57,12 @@ class Sec1KeyParser implements KeyParser {
 		if (encodedKey[0] != 4) throw new GeneralSecurityException();
 		// The x co-ordinate must be >= 0 and < p
 		byte[] xBytes = new byte[bytesPerInt];
-		System.arraycopy(encodedKey, 1, xBytes, 0, bytesPerInt);
+		arraycopy(encodedKey, 1, xBytes, 0, bytesPerInt);
 		BigInteger x = new BigInteger(1, xBytes); // Positive signum
 		if (x.compareTo(modulus) >= 0) throw new GeneralSecurityException();
 		// The y co-ordinate must be >= 0 and < p
 		byte[] yBytes = new byte[bytesPerInt];
-		System.arraycopy(encodedKey, 1 + bytesPerInt, yBytes, 0, bytesPerInt);
+		arraycopy(encodedKey, 1 + bytesPerInt, yBytes, 0, bytesPerInt);
 		BigInteger y = new BigInteger(1, yBytes); // Positive signum
 		if (y.compareTo(modulus) >= 0) throw new GeneralSecurityException();
 		// Verify that y^2 == x^3 + ax + b (mod p)

bramble-core/src/main/java/org/briarproject/bramble/crypto/Sec1Utils.java

@@ -2,6 +2,8 @@ package org.briarproject.bramble.crypto;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
+import static java.lang.System.arraycopy;
+
 @NotNullByDefault
 class Sec1Utils {
 
@@ -10,10 +12,10 @@ class Sec1Utils {
 		if (src.length < destLen) {
 			int padding = destLen - src.length;
 			for (int i = destOff; i < destOff + padding; i++) dest[i] = 0;
-			System.arraycopy(src, 0, dest, destOff + padding, src.length);
+			arraycopy(src, 0, dest, destOff + padding, src.length);
 		} else {
 			int srcOff = src.length - destLen;
-			System.arraycopy(src, srcOff, dest, destOff, destLen);
+			arraycopy(src, srcOff, dest, destOff, destLen);
 		}
 	}
 }

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

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamDecrypter;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.ByteUtils;
 
 import java.io.EOFException;
 import java.io.IOException;
@@ -14,6 +13,7 @@ import java.security.GeneralSecurityException;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_HEADER_PLAINTEXT_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_NONCE_LENGTH;
@@ -26,6 +26,8 @@ import static org.briarproject.bramble.api.transport.TransportConstants.STREAM_H
 import static org.briarproject.bramble.api.transport.TransportConstants.STREAM_HEADER_PLAINTEXT_LENGTH;
 import static org.briarproject.bramble.util.ByteUtils.INT_16_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.readUint16;
+import static org.briarproject.bramble.util.ByteUtils.readUint64;
 
 @NotThreadSafe
 @NotNullByDefault
@@ -130,7 +132,7 @@ class StreamDecrypterImpl implements StreamDecrypter {
 		}
 		// Extract the nonce
 		byte[] streamHeaderNonce = new byte[STREAM_HEADER_NONCE_LENGTH];
-		System.arraycopy(streamHeaderCiphertext, 0, streamHeaderNonce, 0,
+		arraycopy(streamHeaderCiphertext, 0, streamHeaderNonce, 0,
 				STREAM_HEADER_NONCE_LENGTH);
 		// Decrypt and authenticate the stream header
 		try {
@@ -145,17 +147,16 @@ class StreamDecrypterImpl implements StreamDecrypter {
 			throw new FormatException();
 		}
 		// Check the protocol version
-		int receivedProtocolVersion =
-				ByteUtils.readUint16(streamHeaderPlaintext, 0);
+		int receivedProtocolVersion = readUint16(streamHeaderPlaintext, 0);
 		if (receivedProtocolVersion != PROTOCOL_VERSION)
 			throw new FormatException();
 		// Check the stream number
-		long receivedStreamNumber = ByteUtils.readUint64(streamHeaderPlaintext,
+		long receivedStreamNumber = readUint64(streamHeaderPlaintext,
 				INT_16_BYTES);
 		if (receivedStreamNumber != streamNumber) throw new FormatException();
 		// Extract the frame key
 		byte[] frameKeyBytes = new byte[SecretKey.LENGTH];
-		System.arraycopy(streamHeaderPlaintext, INT_16_BYTES + INT_64_BYTES,
+		arraycopy(streamHeaderPlaintext, INT_16_BYTES + INT_64_BYTES,
 				frameKeyBytes, 0, SecretKey.LENGTH);
 		frameKey = new SecretKey(frameKeyBytes);
 	}

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

@@ -3,7 +3,6 @@ package org.briarproject.bramble.crypto;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.StreamEncrypter;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.ByteUtils;
 
 import java.io.IOException;
 import java.io.OutputStream;
@@ -12,6 +11,7 @@ import java.security.GeneralSecurityException;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_HEADER_PLAINTEXT_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.FRAME_NONCE_LENGTH;
@@ -24,6 +24,8 @@ import static org.briarproject.bramble.api.transport.TransportConstants.STREAM_H
 import static org.briarproject.bramble.api.transport.TransportConstants.STREAM_HEADER_PLAINTEXT_LENGTH;
 import static org.briarproject.bramble.util.ByteUtils.INT_16_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint64;
 
 @NotThreadSafe
 @NotNullByDefault
@@ -88,7 +90,7 @@ class StreamEncrypterImpl implements StreamEncrypter {
 			throw new RuntimeException(badCipher);
 		}
 		// Combine the payload and padding
-		System.arraycopy(payload, 0, framePlaintext, 0, payloadLength);
+		arraycopy(payload, 0, framePlaintext, 0, payloadLength);
 		for (int i = 0; i < paddingLength; i++)
 			framePlaintext[payloadLength + i] = 0;
 		// Encrypt and authenticate the payload and padding
@@ -118,13 +120,12 @@ class StreamEncrypterImpl implements StreamEncrypter {
 	private void writeStreamHeader() throws IOException {
 		// The header contains the protocol version, stream number and frame key
 		byte[] streamHeaderPlaintext = new byte[STREAM_HEADER_PLAINTEXT_LENGTH];
-		ByteUtils.writeUint16(PROTOCOL_VERSION, streamHeaderPlaintext, 0);
-		ByteUtils.writeUint64(streamNumber, streamHeaderPlaintext,
-				INT_16_BYTES);
-		System.arraycopy(frameKey.getBytes(), 0, streamHeaderPlaintext,
+		writeUint16(PROTOCOL_VERSION, streamHeaderPlaintext, 0);
+		writeUint64(streamNumber, streamHeaderPlaintext, INT_16_BYTES);
+		arraycopy(frameKey.getBytes(), 0, streamHeaderPlaintext,
 				INT_16_BYTES + INT_64_BYTES, SecretKey.LENGTH);
 		byte[] streamHeaderCiphertext = new byte[STREAM_HEADER_LENGTH];
-		System.arraycopy(streamHeaderNonce, 0, streamHeaderCiphertext, 0,
+		arraycopy(streamHeaderNonce, 0, streamHeaderCiphertext, 0,
 				STREAM_HEADER_NONCE_LENGTH);
 		// Encrypt and authenticate the stream header key
 		try {

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

@@ -7,13 +7,12 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.OutgoingKeys;
 import org.briarproject.bramble.api.transport.TransportKeys;
-import org.briarproject.bramble.util.ByteUtils;
-import org.briarproject.bramble.util.StringUtils;
 import org.spongycastle.crypto.Digest;
 import org.spongycastle.crypto.digests.Blake2bDigest;
 
 import javax.inject.Inject;
 
+import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_HEADER_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_TAG_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.BOB_HEADER_LABEL;
@@ -24,6 +23,9 @@ import static org.briarproject.bramble.util.ByteUtils.INT_16_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.MAX_16_BIT_UNSIGNED;
 import static org.briarproject.bramble.util.ByteUtils.MAX_32_BIT_UNSIGNED;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint64;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 class TransportCryptoImpl implements TransportCrypto {
 
@@ -91,21 +93,21 @@ class TransportCryptoImpl implements TransportCrypto {
 
 	private SecretKey rotateKey(SecretKey k, long rotationPeriod) {
 		byte[] period = new byte[INT_64_BYTES];
-		ByteUtils.writeUint64(rotationPeriod, period, 0);
+		writeUint64(rotationPeriod, period, 0);
 		return crypto.deriveKey(ROTATE_LABEL, k, period);
 	}
 
 	private SecretKey deriveTagKey(SecretKey master, TransportId t,
 			boolean alice) {
 		String label = alice ? ALICE_TAG_LABEL : BOB_TAG_LABEL;
-		byte[] id = StringUtils.toUtf8(t.getString());
+		byte[] id = toUtf8(t.getString());
 		return crypto.deriveKey(label, master, id);
 	}
 
 	private SecretKey deriveHeaderKey(SecretKey master, TransportId t,
 			boolean alice) {
 		String label = alice ? ALICE_HEADER_LABEL : BOB_HEADER_LABEL;
-		byte[] id = StringUtils.toUtf8(t.getString());
+		byte[] id = toUtf8(t.getString());
 		return crypto.deriveKey(label, master, id);
 	}
 
@@ -125,14 +127,14 @@ class TransportCryptoImpl implements TransportCrypto {
 		// The input is the protocol version as a 16-bit integer, followed by
 		// the stream number as a 64-bit integer
 		byte[] protocolVersionBytes = new byte[INT_16_BYTES];
-		ByteUtils.writeUint16(protocolVersion, protocolVersionBytes, 0);
+		writeUint16(protocolVersion, protocolVersionBytes, 0);
 		prf.update(protocolVersionBytes, 0, protocolVersionBytes.length);
 		byte[] streamNumberBytes = new byte[INT_64_BYTES];
-		ByteUtils.writeUint64(streamNumber, streamNumberBytes, 0);
+		writeUint64(streamNumber, streamNumberBytes, 0);
 		prf.update(streamNumberBytes, 0, streamNumberBytes.length);
 		byte[] mac = new byte[macLength];
 		prf.doFinal(mac, 0);
 		// The output is the first TAG_LENGTH bytes of the MAC
-		System.arraycopy(mac, 0, tag, 0, TAG_LENGTH);
+		arraycopy(mac, 0, tag, 0, TAG_LENGTH);
 	}
 }

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.
@@ -242,7 +242,7 @@ interface Database<T> {
 	 * bytes. This is based on the minimum of the space available on the device
 	 * where the database is stored and the database's configured size.
 	 */
-	long getFreeSpace() throws DbException;
+	long getFreeSpace();
 
 	/**
 	 * Returns the group with the given ID.
@@ -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

@@ -43,7 +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;
@@ -55,13 +54,13 @@ 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;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -72,11 +71,13 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.Collections.singletonList;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 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.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_OFFERED_MESSAGES;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -87,7 +88,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	private static final Logger LOG =
-			Logger.getLogger(DatabaseComponentImpl.class.getName());
+			getLogger(DatabaseComponentImpl.class.getName());
 
 	private final Database<T> db;
 	private final Class<T> txnClass;
@@ -579,7 +580,7 @@ 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))
@@ -619,8 +620,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependencies(Transaction transaction,
-			MessageId m) throws DbException {
+	public Map<MessageId, MessageState> getMessageDependencies(
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -628,8 +629,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependents(Transaction transaction,
-			MessageId m) throws DbException {
+	public Map<MessageId, MessageState> getMessageDependents(
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -898,7 +899,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		if (old == INVISIBLE) db.addGroupVisibility(txn, c, g, v == SHARED);
 		else if (v == INVISIBLE) db.removeGroupVisibility(txn, c, g);
 		else db.setGroupVisibility(txn, c, g, v == SHARED);
-		List<ContactId> affected = Collections.singletonList(c);
+		List<ContactId> affected = singletonList(c);
 		transaction.attach(new GroupVisibilityUpdatedEvent(affected));
 	}
 
@@ -918,7 +919,7 @@ 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))
@@ -935,10 +936,10 @@ 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,
-					dependentState);
+			db.addMessageDependency(txn, dependent, dependency, dependentState);
 		}
 	}
 

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

@@ -7,7 +7,6 @@ import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.io.File;
 import java.sql.Connection;
@@ -15,16 +14,24 @@ 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;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 /**
  * 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";
@@ -100,7 +107,7 @@ class H2Database extends JdbcDatabase {
 		Properties props = new Properties();
 		props.setProperty("user", "user");
 		// Separate the file password from the user password with a space
-		String hex = StringUtils.toHexString(key.getBytes());
+		String hex = toHexString(key.getBytes());
 		props.put("password", hex + " password");
 		return DriverManager.getConnection(getUrl(), props);
 	}
@@ -121,8 +128,8 @@ class H2Database extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
-			tryToClose(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -7,23 +7,31 @@ import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.io.File;
 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;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 /**
  * 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(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -106,7 +114,7 @@ class HyperSqlDatabase extends JdbcDatabase {
 	protected Connection createConnection() throws SQLException {
 		SecretKey key = this.key;
 		if (key == null) throw new IllegalStateException();
-		String hex = StringUtils.toHexString(key.getBytes());
+		String hex = toHexString(key.getBytes());
 		return DriverManager.getConnection(url + ";crypt_key=" + hex);
 	}
 
@@ -122,8 +130,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
-			tryToClose(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, 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

@@ -7,15 +7,13 @@ 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 java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration38_39 implements Migration<Connection> {
 
-	private static final Logger LOG =
-			Logger.getLogger(Migration38_39.class.getName());
+	private static final Logger LOG = getLogger(Migration38_39.class.getName());
 
 	@Override
 	public int getStartVersion() {
@@ -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

@@ -7,15 +7,13 @@ 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 java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration39_40 implements Migration<Connection> {
 
-	private static final Logger LOG =
-			Logger.getLogger(Migration39_40.class.getName());
+	private static final Logger LOG = getLogger(Migration39_40.class.getName());
 
 	@Override
 	public int getStartVersion() {
@@ -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> {
 
@@ -19,7 +17,7 @@ class Migration40_41 implements Migration<Connection> {
 
 	private final DatabaseTypes dbTypes;
 
-	public Migration40_41(DatabaseTypes databaseTypes) {
+	Migration40_41(DatabaseTypes databaseTypes) {
 		this.dbTypes = databaseTypes;
 	}
 
@@ -41,16 +39,8 @@ class Migration40_41 implements Migration<Connection> {
 			s.execute("ALTER TABLE contacts"
 					+ 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/AuthorFactoryImpl.java

@@ -7,8 +7,6 @@ import org.briarproject.bramble.api.identity.AuthorId;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.util.ByteUtils;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
@@ -16,6 +14,8 @@ import javax.inject.Inject;
 import static org.briarproject.bramble.api.identity.Author.FORMAT_VERSION;
 import static org.briarproject.bramble.api.identity.AuthorId.LABEL;
 import static org.briarproject.bramble.util.ByteUtils.INT_32_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.writeUint32;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 @Immutable
 @NotNullByDefault
@@ -58,8 +58,8 @@ class AuthorFactoryImpl implements AuthorFactory {
 
 	private AuthorId getId(int formatVersion, String name, byte[] publicKey) {
 		byte[] formatVersionBytes = new byte[INT_32_BYTES];
-		ByteUtils.writeUint32(formatVersion, formatVersionBytes, 0);
+		writeUint32(formatVersion, formatVersionBytes, 0);
 		return new AuthorId(crypto.hash(LABEL, formatVersionBytes,
-				StringUtils.toUtf8(name), publicKey));
+				toUtf8(name), publicKey));
 	}
 }

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

@@ -16,6 +16,7 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
 
@@ -24,7 +25,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class IdentityManagerImpl implements IdentityManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(IdentityManagerImpl.class.getName());
+			getLogger(IdentityManagerImpl.class.getName());
 
 	private final DatabaseComponent db;
 	private final CryptoComponent crypto;

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

@@ -2,7 +2,7 @@ package org.briarproject.bramble.keyagreement;
 
 class AbortException extends Exception {
 
-	boolean receivedAbort;
+	final boolean receivedAbort;
 
 	AbortException() {
 		this(false);

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

@@ -20,13 +20,14 @@ import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
 @NotNullByDefault
 @ThreadSafe
 class ConnectionChooserImpl implements ConnectionChooser {
 
 	private static final Logger LOG =
-			Logger.getLogger(ConnectionChooserImpl.class.getName());
+			getLogger(ConnectionChooserImpl.class.getName());
 
 	private final Clock clock;
 	private final Executor ioExecutor;

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

@@ -30,6 +30,7 @@ import javax.annotation.Nullable;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.CONNECTION_TIMEOUT;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
@@ -41,7 +42,7 @@ class KeyAgreementConnector {
 	}
 
 	private static final Logger LOG =
-			Logger.getLogger(KeyAgreementConnector.class.getName());
+			getLogger(KeyAgreementConnector.class.getName());
 
 	private final Callbacks callbacks;
 	private final KeyAgreementCrypto keyAgreementCrypto;

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

@@ -28,6 +28,7 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @MethodsNotNullByDefault
@@ -36,7 +37,7 @@ class KeyAgreementTaskImpl extends Thread implements KeyAgreementTask,
 		KeyAgreementProtocol.Callbacks, KeyAgreementConnector.Callbacks {
 
 	private static final Logger LOG =
-			Logger.getLogger(KeyAgreementTaskImpl.class.getName());
+			getLogger(KeyAgreementTaskImpl.class.getName());
 
 	private final CryptoComponent crypto;
 	private final KeyAgreementCrypto keyAgreementCrypto;

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

@@ -16,6 +16,7 @@ import java.io.OutputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
 import static org.briarproject.bramble.api.keyagreement.RecordTypes.ABORT;
 import static org.briarproject.bramble.api.keyagreement.RecordTypes.CONFIRM;
@@ -29,7 +30,7 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 class KeyAgreementTransport {
 
 	private static final Logger LOG =
-			Logger.getLogger(KeyAgreementTransport.class.getName());
+			getLogger(KeyAgreementTransport.class.getName());
 
 	private final KeyAgreementConnection kac;
 	private final RecordReader reader;

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

@@ -28,6 +28,7 @@ import javax.inject.Inject;
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.COMPACTING_DATABASE;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.MIGRATING_DATABASE;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
@@ -49,7 +50,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(LifecycleManagerImpl.class.getName());
+			getLogger(LifecycleManagerImpl.class.getName());
 
 	private final DatabaseComponent db;
 	private final EventBus eventBus;

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

@@ -26,13 +26,14 @@ import java.util.logging.Logger;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENGTH;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 class ConnectionManagerImpl implements ConnectionManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(ConnectionManagerImpl.class.getName());
+			getLogger(ConnectionManagerImpl.class.getName());
 
 	private final Executor ioExecutor;
 	private final KeyManager keyManager;

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

@@ -13,7 +13,6 @@ import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -24,14 +23,16 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.Collections.emptyList;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
 @ThreadSafe
 @NotNullByDefault
 class ConnectionRegistryImpl implements ConnectionRegistry {
 
 	private static final Logger LOG =
-			Logger.getLogger(ConnectionRegistryImpl.class.getName());
+			getLogger(ConnectionRegistryImpl.class.getName());
 
 	private final EventBus eventBus;
 	private final Lock lock = new ReentrantLock();
@@ -103,7 +104,7 @@ class ConnectionRegistryImpl implements ConnectionRegistry {
 		lock.lock();
 		try {
 			Multiset<ContactId> m = connections.get(t);
-			if (m == null) return Collections.emptyList();
+			if (m == null) return emptyList();
 			List<ContactId> ids = new ArrayList<>(m.keySet());
 			if (LOG.isLoggable(INFO))
 				LOG.info(ids.size() + " contacts connected: " + t);

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

@@ -52,6 +52,7 @@ import javax.inject.Inject;
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
@@ -61,7 +62,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class PluginManagerImpl implements PluginManager, Service {
 
 	private static final Logger LOG =
-			Logger.getLogger(PluginManagerImpl.class.getName());
+			getLogger(PluginManagerImpl.class.getName());
 
 	private final Executor ioExecutor;
 	private final ScheduledExecutorService scheduler;

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

@@ -36,18 +36,20 @@ import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @ThreadSafe
 @NotNullByDefault
 class Poller implements EventListener {
 
-	private static final Logger LOG = Logger.getLogger(Poller.class.getName());
+	private static final Logger LOG = getLogger(Poller.class.getName());
 
 	private final Executor ioExecutor;
 	private final ScheduledExecutorService scheduler;
@@ -58,7 +60,8 @@ class Poller implements EventListener {
 	private final SecureRandom random;
 	private final Clock clock;
 	private final Lock lock;
-	private final Map<TransportId, ScheduledPollTask> tasks; // Locking: lock
+	@GuardedBy("lock")
+	private final Map<TransportId, ScheduledPollTask> tasks;
 
 	Poller(@IoExecutor Executor ioExecutor,
 			@Scheduler ScheduledExecutorService scheduler,

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

@@ -20,6 +20,7 @@ interface BluetoothConnectionLimiter {
 	 * Returns true if a contact connection can be opened. This method does not
 	 * need to be called for key agreement connections.
 	 */
+	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 	boolean canOpenContactConnection();
 
 	/**

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

@@ -13,6 +13,7 @@ import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
@@ -20,7 +21,7 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 
 	private static final Logger LOG =
-			Logger.getLogger(BluetoothConnectionLimiterImpl.class.getName());
+			getLogger(BluetoothConnectionLimiterImpl.class.getName());
 
 	private final Object lock = new Object();
 	// The following are locking: lock

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

@@ -37,6 +37,7 @@ import javax.annotation.Nullable;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_BLUETOOTH;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.PREF_BT_ENABLE;
@@ -54,7 +55,7 @@ import static org.briarproject.bramble.util.StringUtils.macToString;
 abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(BluetoothPlugin.class.getName());
+			getLogger(BluetoothPlugin.class.getName());
 
 	final BluetoothConnectionLimiter connectionLimiter;
 

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

@@ -14,6 +14,7 @@ import java.io.IOException;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.plugin.FileConstants.PROP_PATH;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
@@ -21,8 +22,7 @@ import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 @NotNullByDefault
 abstract class FilePlugin implements SimplexPlugin {
 
-	private static final Logger LOG =
-			Logger.getLogger(FilePlugin.class.getName());
+	private static final Logger LOG = getLogger(FilePlugin.class.getName());
 
 	protected final SimplexPluginCallback callback;
 	protected final int maxLatency;

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

@@ -4,18 +4,18 @@ 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 java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportReader implements TransportConnectionReader {
 
 	private static final Logger LOG =
-			Logger.getLogger(FileTransportReader.class.getName());
+			getLogger(FileTransportReader.class.getName());
 
 	private final File file;
 	private final InputStream in;
@@ -34,11 +34,7 @@ class FileTransportReader implements TransportConnectionReader {
 
 	@Override
 	public void dispose(boolean exception, boolean recognised) {
-		try {
-			in.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		tryToClose(in, LOG, WARNING);
 		plugin.readerFinished(file, exception, recognised);
 	}
 }

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

@@ -4,18 +4,18 @@ 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 java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportWriter implements TransportConnectionWriter {
 
 	private static final Logger LOG =
-			Logger.getLogger(FileTransportWriter.class.getName());
+			getLogger(FileTransportWriter.class.getName());
 
 	private final File file;
 	private final OutputStream out;
@@ -44,11 +44,7 @@ class FileTransportWriter implements TransportConnectionWriter {
 
 	@Override
 	public void dispose(boolean exception) {
-		try {
-			out.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		tryToClose(out, LOG, WARNING);
 		plugin.writerFinished(file, exception);
 	}
 }

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

@@ -11,7 +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.StringUtils;
+import org.briarproject.bramble.util.IoUtils;
 
 import java.io.IOException;
 import java.net.Inet4Address;
@@ -22,27 +22,30 @@ import java.net.Socket;
 import java.net.SocketAddress;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
+import static java.util.Collections.addAll;
+import static java.util.Collections.emptyList;
+import static java.util.Collections.sort;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.ID;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PREF_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;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
+import static org.briarproject.bramble.util.StringUtils.join;
 
 @NotNullByDefault
 class LanTcpPlugin extends TcpPlugin {
 
-	private static final Logger LOG =
-			Logger.getLogger(LanTcpPlugin.class.getName());
+	private static final Logger LOG = getLogger(LanTcpPlugin.class.getName());
 
 	private static final LanAddressComparator ADDRESS_COMPARATOR =
 			new LanAddressComparator();
@@ -77,12 +80,13 @@ class LanTcpPlugin extends TcpPlugin {
 				locals.add(new InetSocketAddress(local, 0));
 			}
 		}
-		Collections.sort(locals, ADDRESS_COMPARATOR);
+		//noinspection Java8ListSort
+		sort(locals, ADDRESS_COMPARATOR);
 		return locals;
 	}
 
 	private List<InetSocketAddress> parseSocketAddresses(String ipPorts) {
-		if (StringUtils.isNullOrEmpty(ipPorts)) return Collections.emptyList();
+		if (isNullOrEmpty(ipPorts)) return emptyList();
 		String[] split = ipPorts.split(SEPARATOR);
 		List<InetSocketAddress> addresses = new ArrayList<>();
 		for (String ipPort : split) {
@@ -98,24 +102,23 @@ class LanTcpPlugin extends TcpPlugin {
 		// Get the list of recently used addresses
 		String setting = callback.getSettings().get(PREF_LAN_IP_PORTS);
 		List<String> recent = new ArrayList<>();
-		if (!StringUtils.isNullOrEmpty(setting))
-			Collections.addAll(recent, setting.split(SEPARATOR));
+		if (!isNullOrEmpty(setting)) addAll(recent, setting.split(SEPARATOR));
 		// Is the address already in the list?
 		if (recent.remove(ipPort)) {
 			// Move the address to the start of the list
 			recent.add(0, ipPort);
-			setting = StringUtils.join(recent, SEPARATOR);
+			setting = join(recent, SEPARATOR);
 		} else {
 			// Add the address to the start of the list
 			recent.add(0, ipPort);
 			// Drop the least recently used address if the list is full
 			if (recent.size() > MAX_ADDRESSES)
 				recent = recent.subList(0, MAX_ADDRESSES);
-			setting = StringUtils.join(recent, SEPARATOR);
+			setting = join(recent, SEPARATOR);
 			// Update the list of addresses shared with contacts
 			List<String> shared = new ArrayList<>(recent);
-			Collections.sort(shared);
-			String property = StringUtils.join(shared, SEPARATOR);
+			sort(shared);
+			String property = join(shared, SEPARATOR);
 			TransportProperties properties = new TransportProperties();
 			properties.put(PROP_IP_PORTS, property);
 			callback.mergeLocalProperties(properties);
@@ -293,11 +296,7 @@ class LanTcpPlugin extends TcpPlugin {
 
 		@Override
 		public void close() {
-			try {
-				ss.close();
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-			}
+			IoUtils.tryToClose(ss, LOG, WARNING);
 		}
 	}
 

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

@@ -17,6 +17,7 @@ import javax.xml.parsers.ParserConfigurationException;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubInetAddress;
 
@@ -25,8 +26,7 @@ import static org.briarproject.bramble.util.PrivacyUtils.scrubInetAddress;
 @ParametersNotNullByDefault
 class PortMapperImpl implements PortMapper {
 
-	private static final Logger LOG =
-			Logger.getLogger(PortMapperImpl.class.getName());
+	private static final Logger LOG = getLogger(PortMapperImpl.class.getName());
 
 	private final ShutdownManager shutdownManager;
 	private final AtomicBoolean started = new AtomicBoolean(false);

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

@@ -11,7 +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.StringUtils;
+import org.briarproject.bramble.util.IoUtils;
 
 import java.io.IOException;
 import java.net.InetAddress;
@@ -40,17 +40,19 @@ import static java.util.Collections.emptyList;
 import static java.util.Collections.list;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubSocketAddress;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
 abstract class TcpPlugin implements DuplexPlugin {
 
+	private static final Logger LOG = getLogger(TcpPlugin.class.getName());
+
 	private static final Pattern DOTTED_QUAD =
 			Pattern.compile("^\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}$");
-	private static final Logger LOG =
-			Logger.getLogger(TcpPlugin.class.getName());
 
 	protected final Executor ioExecutor, bindExecutor;
 	protected final Backoff backoff;
@@ -83,6 +85,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 	/**
 	 * Returns true if connections to the given address can be attempted.
 	 */
+	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 	protected abstract boolean isConnectable(InetSocketAddress remote);
 
 	TcpPlugin(Executor ioExecutor, Backoff backoff,
@@ -153,13 +156,8 @@ abstract class TcpPlugin implements DuplexPlugin {
 	}
 
 	protected void tryToClose(@Nullable ServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
+		callback.transportDisabled();
 	}
 
 	String getIpPortString(InetSocketAddress a) {
@@ -267,7 +265,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 
 	@Nullable
 	InetSocketAddress parseSocketAddress(String ipPort) {
-		if (StringUtils.isNullOrEmpty(ipPort)) return null;
+		if (isNullOrEmpty(ipPort)) return null;
 		String[] split = ipPort.split(":");
 		if (split.length != 2) return null;
 		String addr = split[0], port = split[1];

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

@@ -10,11 +10,12 @@ import org.briarproject.bramble.api.properties.TransportProperties;
 import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
-import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.Executor;
 
+import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
 import static org.briarproject.bramble.api.plugin.WanTcpConstants.ID;
 
 @MethodsNotNullByDefault
@@ -80,8 +81,7 @@ class WanTcpPlugin extends TcpPlugin {
 	protected List<InetSocketAddress> getRemoteSocketAddresses(
 			TransportProperties p) {
 		InetSocketAddress parsed = parseSocketAddress(p.get(PROP_IP_PORT));
-		if (parsed == null) return Collections.emptyList();
-		return Collections.singletonList(parsed);
+		return parsed == null ? emptyList() : singletonList(parsed);
 	}
 
 	@Override

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

@@ -31,7 +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;
@@ -43,9 +42,7 @@ import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -59,8 +56,12 @@ import java.util.zip.ZipInputStream;
 import javax.annotation.Nullable;
 import javax.net.SocketFactory;
 
+import static java.util.Arrays.asList;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static net.freehaven.tor.control.TorControlCommands.HS_ADDRESS;
 import static net.freehaven.tor.control.TorControlCommands.HS_PRIVKEY;
 import static org.briarproject.bramble.api.plugin.TorConstants.CONTROL_PORT;
@@ -70,9 +71,11 @@ 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;
+import static org.briarproject.bramble.util.IoUtils.copyAndClose;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubOnion;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
@@ -81,8 +84,7 @@ import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 @ParametersNotNullByDefault
 abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
-	private static final Logger LOG =
-			Logger.getLogger(TorPlugin.class.getName());
+	private static final Logger LOG = getLogger(TorPlugin.class.getName());
 
 	private static final String[] EVENTS = {
 			"CIRC", "ORCONN", "HS_DESC", "NOTICE", "WARN", "ERR"
@@ -251,11 +253,11 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			controlConnection.authenticate(read(cookieFile));
 			// Tell Tor to exit when the control connection is closed
 			controlConnection.takeOwnership();
-			controlConnection.resetConf(Collections.singletonList(OWNER));
+			controlConnection.resetConf(singletonList(OWNER));
 			running = true;
 			// Register to receive events from the Tor process
 			controlConnection.setEventHandler(this);
-			controlConnection.setEvents(Arrays.asList(EVENTS));
+			controlConnection.setEvents(asList(EVENTS));
 			// Check whether Tor has already bootstrapped
 			String phase = controlConnection.getInfo("status/bootstrap-phase");
 			if (phase != null && phase.contains("PROGRESS=100")) {
@@ -280,31 +282,34 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		InputStream in = null;
 		OutputStream out = null;
 		try {
+			// The done file may already exist from a previous installation
+			//noinspection ResultOfMethodCallIgnored
 			doneFile.delete();
 			// Unzip the Tor binary to the filesystem
 			in = getTorInputStream();
 			out = new FileOutputStream(torFile);
-			IoUtils.copyAndClose(in, out);
+			copyAndClose(in, out);
 			// Make the Tor binary executable
 			if (!torFile.setExecutable(true, true)) throw new IOException();
 			// Unzip the GeoIP database to the filesystem
 			in = getGeoIpInputStream();
 			out = new FileOutputStream(geoIpFile);
-			IoUtils.copyAndClose(in, out);
+			copyAndClose(in, out);
 			// Unzip the Obfs4 proxy to the filesystem
 			in = getObfs4InputStream();
 			out = new FileOutputStream(obfs4File);
-			IoUtils.copyAndClose(in, out);
+			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();
+			copyAndClose(in, out);
+			if (!doneFile.createNewFile())
+				LOG.warning("Failed to create done file");
 		} catch (IOException e) {
-			tryToClose(in);
-			tryToClose(out);
+			IoUtils.tryToClose(in, LOG, WARNING);
+			IoUtils.tryToClose(out, LOG, WARNING);
 			throw new PluginException(e);
 		}
 	}
@@ -341,22 +346,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		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();
@@ -378,7 +367,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			}
 			return b;
 		} finally {
-			tryToClose(in);
+			IoUtils.tryToClose(in, LOG, WARNING);
 		}
 	}
 
@@ -418,21 +407,15 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void tryToClose(@Nullable ServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
+		callback.transportDisabled();
 	}
 
 	private void publishHiddenService(String port) {
 		if (!running) return;
 		LOG.info("Creating hidden service");
 		String privKey = settings.get(HS_PRIVKEY);
-		Map<Integer, String> portLines =
-				Collections.singletonMap(80, "127.0.0.1:" + port);
+		Map<Integer, String> portLines = singletonMap(80, "127.0.0.1:" + port);
 		Map<String, String> response;
 		try {
 			// Use the control connection to set up the hidden service
@@ -593,7 +576,7 @@ 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;
 		}
 	}
@@ -670,8 +653,10 @@ 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
-				// replaced with callback.transportDisabled() when fixed.
+				// Works around a bug introduced in Tor 0.3.4.8.
+				// https://trac.torproject.org/projects/tor/ticket/28027
+				// Could be replaced with callback.transportDisabled()
+				// when fixed.
 				disableNetwork();
 				updateConnectionStatus(networkManager.getNetworkStatus(),
 						batteryManager.isCharging());
@@ -707,6 +692,8 @@ 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;
 
@@ -721,9 +708,12 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				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");

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;