@GuardedBy annotations.

.idea/codeStyles/Project.xml

@@ -39,6 +39,31 @@
     <JetCodeStyleSettings>
       <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
     </JetCodeStyleSettings>
+    <Objective-C-extensions>
+      <file>
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Import" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Macro" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Typedef" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Enum" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Constant" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Global" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Struct" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="FunctionPredecl" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Function" />
+      </file>
+      <class>
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Property" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Synthesize" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InitMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="StaticMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InstanceMethod" />
+        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="DeallocMethod" />
+      </class>
+      <extensions>
+        <pair source="cpp" header="h" fileNamingConvention="NONE" />
+        <pair source="c" header="h" fileNamingConvention="NONE" />
+      </extensions>
+    </Objective-C-extensions>
     <XML>
       <option name="XML_LEGACY_SETTINGS_IMPORTED" value="true" />
     </XML>

bramble-android/build.gradle

@@ -30,8 +30,8 @@ configurations {
 
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
-	tor 'org.briarproject:tor-android:0.3.5.8@zip'
-	tor 'org.briarproject:obfs4proxy-android:0.0.9@zip'
+	tor 'org.briarproject:tor-android:0.3.4.8@zip'
+	tor 'org.briarproject:obfs4proxy-android:0.0.7@zip'
 
 	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
 

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/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/plugin/bluetooth/AndroidBluetoothPlugin.java

@@ -24,7 +24,6 @@ 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;
@@ -48,9 +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 java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
@@ -58,7 +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;
 
@@ -259,7 +260,7 @@ 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;
 	}
 

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

@@ -8,7 +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;
@@ -23,6 +22,9 @@ 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
@@ -45,8 +47,8 @@ class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 		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);
@@ -74,15 +76,13 @@ class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 		// 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 UnixSecureRandomSpi().engineGenerateSeed(
-				SEED_LENGTH);
+		byte[] seed = new UnixSecureRandomSpi().engineGenerateSeed(SEED_LENGTH);
 		try {
 			// Seed the OpenSSL PRNG
 			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-android/witness.gradle

@@ -68,8 +68,8 @@ dependencyVerification {
         'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.bouncycastle:bcpkix-jdk15on:1.56:bcpkix-jdk15on-1.56.jar:7043dee4e9e7175e93e0b36f45b1ec1ecb893c5f755667e8b916eb8dd201c6ca',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
-        'org.briarproject:obfs4proxy-android:0.0.9:obfs4proxy-android-0.0.9.zip:9b7e9181535ea8d8bbe8ae6338e08cf4c5fc1e357a779393e0ce49586d459ae0',
-        'org.briarproject:tor-android:0.3.5.8:tor-android-0.3.5.8.zip:42a13a6f185be1a62f42e3f30ce66a3c099ac5ec890a65e7593111b65b44a54a',
+        'org.briarproject:obfs4proxy-android:0.0.7:obfs4proxy-android-0.0.7.zip:abdfb5d889d848de9bf214f9276abbf454808a505b870819eccc9a9e985bf617',
+        'org.briarproject:tor-android:0.3.4.8:tor-android-0.3.4.8.zip:989a0352d9d8d8172cd6c2137654e165e5d2beb10ed1211bab3814e224ad1926',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.codehaus.groovy:groovy-all:2.4.12:groovy-all-2.4.12.jar:6a56af4bd48903d56bec62821876cadefafd007360cc6bd0d8f7aa8d72b38be4',
         'org.codehaus.mojo:animal-sniffer-annotations:1.14:animal-sniffer-annotations-1.14.jar:2068320bd6bad744c3673ab048f67e30bef8f518996fa380033556600669905d',

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/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

@@ -16,6 +16,7 @@ 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/ContactExchangeListener.java

@@ -0,0 +1,20 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface ContactExchangeListener {
+
+	void contactExchangeSucceeded(Author remoteAuthor);
+
+	/**
+	 * The exchange failed because the contact already exists.
+	 */
+	void duplicateContact(Author remoteAuthor);
+
+	/**
+	 * A general failure.
+	 */
+	void contactExchangeFailed();
+}

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

@@ -41,7 +41,8 @@ public interface ContactExchangeTask {
 	/**
 	 * Exchanges contact information with a remote peer.
 	 */
-	void startExchange(LocalAuthor localAuthor, SecretKey masterSecret,
+	void startExchange(ContactExchangeListener listener,
+			LocalAuthor localAuthor, SecretKey masterSecret,
 			DuplexTransportConnection conn, TransportId transportId,
 			boolean alice);
 }

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

@@ -1,32 +0,0 @@
-package org.briarproject.bramble.api.contact.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.identity.Author;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.Nullable;
-
-@NotNullByDefault
-public class ContactExchangeFailedEvent extends Event {
-
-	@Nullable
-	private final Author duplicateRemoteAuthor;
-
-	public ContactExchangeFailedEvent(@Nullable Author duplicateRemoteAuthor) {
-		this.duplicateRemoteAuthor = duplicateRemoteAuthor;
-	}
-
-	public ContactExchangeFailedEvent() {
-		this(null);
-	}
-
-	@Nullable
-	public Author getDuplicateRemoteAuthor() {
-		return duplicateRemoteAuthor;
-	}
-
-	public boolean wasDuplicateContact() {
-		return duplicateRemoteAuthor != null;
-	}
-
-}

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

@@ -1,20 +0,0 @@
-package org.briarproject.bramble.api.contact.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.identity.Author;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-@NotNullByDefault
-public class ContactExchangeSucceededEvent extends Event {
-
-	private final Author remoteAuthor;
-
-	public ContactExchangeSucceededEvent(Author remoteAuthor) {
-		this.remoteAuthor = remoteAuthor;
-	}
-
-	public Author getRemoteAuthor() {
-		return remoteAuthor;
-	}
-
-}

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/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/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/util/IoUtils.java

@@ -16,12 +16,13 @@ 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()) {

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/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

@@ -2,11 +2,10 @@ package org.briarproject.bramble.contact;
 
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.contact.ContactExchangeListener;
 import org.briarproject.bramble.api.contact.ContactExchangeTask;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
-import org.briarproject.bramble.api.contact.event.ContactExchangeFailedEvent;
-import org.briarproject.bramble.api.contact.event.ContactExchangeSucceededEvent;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.data.BdfDictionary;
@@ -14,7 +13,6 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
@@ -45,6 +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;
@@ -56,7 +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";
@@ -65,7 +64,6 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private final ClientHelper clientHelper;
 	private final RecordReaderFactory recordReaderFactory;
 	private final RecordWriterFactory recordWriterFactory;
-	private final EventBus eventBus;
 	private final Clock clock;
 	private final ConnectionManager connectionManager;
 	private final ContactManager contactManager;
@@ -74,6 +72,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private final StreamReaderFactory streamReaderFactory;
 	private final StreamWriterFactory streamWriterFactory;
 
+	private volatile ContactExchangeListener listener;
 	private volatile LocalAuthor localAuthor;
 	private volatile DuplexTransportConnection conn;
 	private volatile TransportId transportId;
@@ -83,9 +82,8 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	@Inject
 	ContactExchangeTaskImpl(DatabaseComponent db, ClientHelper clientHelper,
 			RecordReaderFactory recordReaderFactory,
-			RecordWriterFactory recordWriterFactory, EventBus eventBus,
-			Clock clock, ConnectionManager connectionManager,
-			ContactManager contactManager,
+			RecordWriterFactory recordWriterFactory, Clock clock,
+			ConnectionManager connectionManager, ContactManager contactManager,
 			TransportPropertyManager transportPropertyManager,
 			CryptoComponent crypto, StreamReaderFactory streamReaderFactory,
 			StreamWriterFactory streamWriterFactory) {
@@ -93,7 +91,6 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 		this.clientHelper = clientHelper;
 		this.recordReaderFactory = recordReaderFactory;
 		this.recordWriterFactory = recordWriterFactory;
-		this.eventBus = eventBus;
 		this.clock = clock;
 		this.connectionManager = connectionManager;
 		this.contactManager = contactManager;
@@ -104,9 +101,11 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	}
 
 	@Override
-	public void startExchange(LocalAuthor localAuthor, SecretKey masterSecret,
+	public void startExchange(ContactExchangeListener listener,
+			LocalAuthor localAuthor, SecretKey masterSecret,
 			DuplexTransportConnection conn, TransportId transportId,
 			boolean alice) {
+		this.listener = listener;
 		this.localAuthor = localAuthor;
 		this.conn = conn;
 		this.transportId = transportId;
@@ -125,8 +124,8 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			out = conn.getWriter().getOutputStream();
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
+			listener.contactExchangeFailed();
 			tryToClose(conn);
-			eventBus.broadcast(new ContactExchangeFailedEvent());
 			return;
 		}
 
@@ -136,7 +135,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			localProperties = transportPropertyManager.getLocalProperties();
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
-			eventBus.broadcast(new ContactExchangeFailedEvent());
+			listener.contactExchangeFailed();
 			tryToClose(conn);
 			return;
 		}
@@ -192,13 +191,14 @@ 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");
 			}
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
-			eventBus.broadcast(new ContactExchangeFailedEvent());
+			listener.contactExchangeFailed();
 			tryToClose(conn);
 			return;
 		}
@@ -206,7 +206,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 		// Verify the contact's signature
 		if (!verify(remoteInfo.author, remoteNonce, remoteInfo.signature)) {
 			LOG.warning("Invalid signature");
-			eventBus.broadcast(new ContactExchangeFailedEvent());
+			listener.contactExchangeFailed();
 			tryToClose(conn);
 			return;
 		}
@@ -223,17 +223,15 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 					conn);
 			// Pseudonym exchange succeeded
 			LOG.info("Pseudonym exchange succeeded");
-			eventBus.broadcast(
-					new ContactExchangeSucceededEvent(remoteInfo.author));
+			listener.contactExchangeSucceeded(remoteInfo.author);
 		} catch (ContactExistsException e) {
 			logException(LOG, WARNING, e);
 			tryToClose(conn);
-			eventBus.broadcast(
-					new ContactExchangeFailedEvent(remoteInfo.author));
+			listener.duplicateContact(remoteInfo.author);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
 			tryToClose(conn);
-			eventBus.broadcast(new ContactExchangeFailedEvent());
+			listener.contactExchangeFailed();
 		}
 	}
 

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

@@ -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.

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

@@ -61,7 +61,6 @@ import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -72,7 +71,9 @@ 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.validation.MessageState.DELIVERED;
@@ -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;
@@ -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));
 	}
 

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;
@@ -23,6 +22,7 @@ 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.
@@ -107,7 +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);
 	}

bramble-core/src/main/java/org/briarproject/bramble/db/HyperSqlDatabase.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;
@@ -22,6 +21,7 @@ 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.
@@ -114,7 +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);
 	}
 

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

@@ -38,9 +38,7 @@ import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedList;
@@ -54,11 +52,17 @@ import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 
+import static java.lang.System.arraycopy;
 import static java.sql.Types.INTEGER;
 import static java.sql.Types.VARCHAR;
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.emptySet;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.db.Metadata.REMOVE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
@@ -309,19 +313,20 @@ abstract class JdbcDatabase implements Database<Connection> {
 			"CREATE INDEX IF NOT EXISTS statusesByContactIdTimestamp"
 					+ " ON statuses (contactId, timestamp)";
 
-	private static final Logger LOG =
-			Logger.getLogger(JdbcDatabase.class.getName());
+	private static final Logger LOG = getLogger(JdbcDatabase.class.getName());
 
 	// Different database libraries use different names for certain types
 	private final MessageFactory messageFactory;
 	private final Clock clock;
 	private final DatabaseTypes dbTypes;
 
-	// Locking: connectionsLock
+	@GuardedBy("connectionsLock")
 	private final LinkedList<Connection> connections = new LinkedList<>();
 
-	private int openConnections = 0; // Locking: connectionsLock
-	private boolean closed = false; // Locking: connectionsLock
+	@GuardedBy("connectionsLock")
+	private int openConnections = 0;
+	@GuardedBy("connectionsLock")
+	private boolean closed = false;
 
 	protected abstract Connection createConnection() throws SQLException;
 
@@ -337,6 +342,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		this.clock = clock;
 	}
 
+	@SuppressWarnings("unused")
 	protected void open(String driverClass, boolean reopen, SecretKey key,
 			@Nullable MigrationListener listener) throws DbException {
 		// Load the JDBC driver
@@ -424,7 +430,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	// Package access for testing
 	List<Migration<Connection>> getMigrations() {
-		return Arrays.asList(
+		return asList(
 				new Migration38_39(),
 				new Migration39_40(),
 				new Migration40_41(dbTypes)
@@ -766,7 +772,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			for (Entry<ContactId, Boolean> e : visibility.entrySet()) {
 				ContactId c = e.getKey();
 				boolean offered = removeOfferedMessage(txn, c, m.getId());
-				boolean seen = offered || (sender != null && c.equals(sender));
+				boolean seen = offered || c.equals(sender);
 				addStatus(txn, m.getId(), c, m.getGroupId(), m.getTimestamp(),
 						raw.length, state, e.getValue(), messageShared,
 						false, seen);
@@ -1536,7 +1542,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (raw == null) throw new MessageDeletedException();
 			if (raw.length <= MESSAGE_HEADER_LENGTH) throw new AssertionError();
 			byte[] body = new byte[raw.length - MESSAGE_HEADER_LENGTH];
-			System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
+			arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
 			return new Message(m, g, timestamp, body);
 		} catch (SQLException e) {
 			tryToClose(rs, LOG, WARNING);
@@ -1596,7 +1602,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (intersection == null) intersection = ids;
 				else intersection.retainAll(ids);
 				// Return early if there are no matches
-				if (intersection.isEmpty()) return Collections.emptySet();
+				if (intersection.isEmpty()) return emptySet();
 			}
 			if (intersection == null) throw new AssertionError();
 			return intersection;
@@ -1645,7 +1651,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			GroupId g, Metadata query) throws DbException {
 		// Retrieve the matching message IDs
 		Collection<MessageId> matches = getMessageIds(txn, g, query);
-		if (matches.isEmpty()) return Collections.emptyMap();
+		if (matches.isEmpty()) return emptyMap();
 		// Retrieve the metadata for each match
 		Map<MessageId, Metadata> all = new HashMap<>(matches.size());
 		for (MessageId m : matches) all.put(m, getMessageMetadata(txn, m));
@@ -2395,7 +2401,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				}
 				ps.close();
 			}
-			if (notRemoved.isEmpty()) return Collections.emptyMap();
+			if (notRemoved.isEmpty()) return emptyMap();
 			// Update any keys that already exist
 			String sql = "UPDATE " + tableName + " SET value = ?"
 					+ " WHERE " + columnName + " = ? AND metaKey = ?";

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

@@ -8,12 +8,12 @@ import java.sql.Statement;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class 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() {

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

@@ -8,12 +8,12 @@ import java.sql.Statement;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class 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() {

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

@@ -17,7 +17,7 @@ class Migration40_41 implements Migration<Connection> {
 
 	private final DatabaseTypes dbTypes;
 
-	public Migration40_41(DatabaseTypes databaseTypes) {
+	Migration40_41(DatabaseTypes databaseTypes) {
 		this.dbTypes = databaseTypes;
 	}
 

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

@@ -8,13 +8,14 @@ import java.io.InputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.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;

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

@@ -8,13 +8,14 @@ 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.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;

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

@@ -12,7 +12,6 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.settings.Settings;
 import org.briarproject.bramble.util.IoUtils;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
 import java.net.Inet4Address;
@@ -23,26 +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.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);

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

@@ -12,7 +12,6 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.util.IoUtils;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
 import java.net.InetAddress;
@@ -41,17 +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;
@@ -84,6 +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,
@@ -263,7 +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/CircumventionProvider.java

@@ -17,24 +17,16 @@ public interface CircumventionProvider {
 	String[] BLOCKED = {"CN", "IR", "EG", "BY", "TR", "SY", "VE"};
 
 	/**
-	 * Countries where obfs4 bridge connection are likely to work.
+	 * Countries where vanilla bridge connection are likely to work.
 	 * Should be a subset of {@link #BLOCKED}.
 	 */
-	String[] BRIDGES = { "CN", "IR", "EG", "BY", "TR", "SY", "VE" };
-
-	/**
-	 * Countries where obfs4 bridges won't work and meek is needed.
-	 * Should be a subset of {@link #BRIDGES}.
-	 */
-	String[] NEEDS_MEEK = {"CN", "IR"};
+	String[] BRIDGES = { "EG", "BY", "TR", "SY", "VE" };
 
 	boolean isTorProbablyBlocked(String countryCode);
 
 	boolean doBridgesWork(String countryCode);
 
-	boolean needsMeek(String countryCode);
-
 	@IoExecutor
-	List<String> getBridges(boolean meek);
+	List<String> getBridges();
 
 }

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

@@ -22,8 +22,6 @@ class CircumventionProviderImpl implements CircumventionProvider {
 			new HashSet<>(asList(BLOCKED));
 	private static final Set<String> BRIDGES_WORK_IN_COUNTRIES =
 			new HashSet<>(asList(BRIDGES));
-	private static final Set<String> BRIDGES_NEED_MEEK =
-			new HashSet<>(asList(NEEDS_MEEK));
 
 	@Nullable
 	private volatile List<String> bridges = null;
@@ -42,14 +40,9 @@ class CircumventionProviderImpl implements CircumventionProvider {
 		return BRIDGES_WORK_IN_COUNTRIES.contains(countryCode);
 	}
 
-	@Override
-	public boolean needsMeek(String countryCode) {
-		return BRIDGES_NEED_MEEK.contains(countryCode);
-	}
-
 	@Override
 	@IoExecutor
-	public List<String> getBridges(boolean useMeek) {
+	public List<String> getBridges() {
 		List<String> bridges = this.bridges;
 		if (bridges != null) return new ArrayList<>(bridges);
 
@@ -60,8 +53,6 @@ class CircumventionProviderImpl implements CircumventionProvider {
 		bridges = new ArrayList<>();
 		while (scanner.hasNextLine()) {
 			String line = scanner.nextLine();
-			boolean isMeekBridge = line.startsWith("Bridge meek");
-			if (useMeek && !isMeekBridge || !useMeek && isMeekBridge) continue;
 			if (!line.startsWith("#")) bridges.add(line);
 		}
 		scanner.close();

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

@@ -42,9 +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;
@@ -58,8 +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;
@@ -73,6 +75,7 @@ import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_ONLY_WHE
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_PORT;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V2;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V3;
+import static org.briarproject.bramble.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")) {
@@ -280,28 +282,31 @@ 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) {
 			IoUtils.tryToClose(in, LOG, WARNING);
 			IoUtils.tryToClose(out, LOG, WARNING);
@@ -410,8 +415,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		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
@@ -470,19 +474,13 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		if (!enable) callback.transportDisabled();
 	}
 
-	private void enableBridges(boolean enable, boolean needsMeek)
-			throws IOException {
+	private void enableBridges(boolean enable) throws IOException {
 		if (enable) {
 			Collection<String> conf = new ArrayList<>();
 			conf.add("UseBridges 1");
-			if (needsMeek) {
-				conf.add("ClientTransportPlugin meek_lite exec " +
-						obfs4File.getAbsolutePath());
-			} else {
-				conf.add("ClientTransportPlugin obfs4 exec " +
-						obfs4File.getAbsolutePath());
-			}
-			conf.addAll(circumventionProvider.getBridges(needsMeek));
+			conf.add("ClientTransportPlugin obfs4 exec " +
+					obfs4File.getAbsolutePath());
+			conf.addAll(circumventionProvider.getBridges());
 			controlConnection.setConf(conf);
 		} else {
 			controlConnection.setConf("UseBridges", "0");
@@ -722,17 +720,12 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 					enableNetwork(false);
 				} else if (network == PREF_TOR_NETWORK_WITH_BRIDGES ||
 						(automatic && bridgesWork)) {
-					if (circumventionProvider.needsMeek(country)) {
-						LOG.info("Enabling network, using meek bridges");
-						enableBridges(true, true);
-					} else {
-						LOG.info("Enabling network, using obfs4 bridges");
-						enableBridges(true, false);
-					}
+					LOG.info("Enabling network, using bridges");
+					enableBridges(true);
 					enableNetwork(true);
 				} else {
 					LOG.info("Enabling network, not using bridges");
-					enableBridges(false, false);
+					enableBridges(false);
 					enableNetwork(true);
 				}
 				if (online && wifi && charging) {

bramble-core/src/main/java/org/briarproject/bramble/record/RecordReaderImpl.java

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.record.Record;
 import org.briarproject.bramble.api.record.RecordReader;
-import org.briarproject.bramble.util.ByteUtils;
 
 import java.io.DataInputStream;
 import java.io.IOException;
@@ -14,6 +13,7 @@ import javax.annotation.concurrent.NotThreadSafe;
 
 import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
 import static org.briarproject.bramble.api.record.Record.RECORD_HEADER_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.readUint16;
 
 @NotThreadSafe
 @NotNullByDefault
@@ -31,7 +31,7 @@ class RecordReaderImpl implements RecordReader {
 		in.readFully(header);
 		byte protocolVersion = header[0];
 		byte recordType = header[1];
-		int payloadLength = ByteUtils.readUint16(header, 2);
+		int payloadLength = readUint16(header, 2);
 		if (payloadLength < 0 || payloadLength > MAX_RECORD_PAYLOAD_BYTES)
 			throw new FormatException();
 		byte[] payload = new byte[payloadLength];

bramble-core/src/main/java/org/briarproject/bramble/record/RecordWriterImpl.java

@@ -3,7 +3,6 @@ package org.briarproject.bramble.record;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.record.Record;
 import org.briarproject.bramble.api.record.RecordWriter;
-import org.briarproject.bramble.util.ByteUtils;
 
 import java.io.IOException;
 import java.io.OutputStream;
@@ -11,6 +10,7 @@ import java.io.OutputStream;
 import javax.annotation.concurrent.NotThreadSafe;
 
 import static org.briarproject.bramble.api.record.Record.RECORD_HEADER_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
 
 @NotThreadSafe
 @NotNullByDefault
@@ -28,7 +28,7 @@ class RecordWriterImpl implements RecordWriter {
 		byte[] payload = r.getPayload();
 		header[0] = r.getProtocolVersion();
 		header[1] = r.getRecordType();
-		ByteUtils.writeUint16(payload.length, header, 2);
+		writeUint16(payload.length, header, 2);
 		out.write(header);
 		out.write(payload);
 	}

bramble-core/src/main/java/org/briarproject/bramble/reliability/Ack.java

@@ -1,10 +1,12 @@
 package org.briarproject.bramble.reliability;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.ByteUtils;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static org.briarproject.bramble.util.ByteUtils.readUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+
 @NotThreadSafe
 @NotNullByDefault
 class Ack extends Frame {
@@ -23,10 +25,10 @@ class Ack extends Frame {
 	}
 
 	int getWindowSize() {
-		return ByteUtils.readUint16(buf, 5);
+		return readUint16(buf, 5);
 	}
 
 	void setWindowSize(int windowSize) {
-		ByteUtils.writeUint16(windowSize, buf, 5);
+		writeUint16(windowSize, buf, 5);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/reliability/Frame.java

@@ -1,17 +1,19 @@
 package org.briarproject.bramble.reliability;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.ByteUtils;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static org.briarproject.bramble.util.ByteUtils.readUint32;
+import static org.briarproject.bramble.util.ByteUtils.writeUint32;
+
 @NotThreadSafe
 @NotNullByDefault
 abstract class Frame {
 
 	static final byte ACK_FLAG = (byte) 128, FIN_FLAG = 64;
 
-	protected final byte[] buf;
+	final byte[] buf;
 
 	Frame(byte[] buf) {
 		this.buf = buf;
@@ -26,11 +28,11 @@ abstract class Frame {
 	}
 
 	long getChecksum() {
-		return ByteUtils.readUint32(buf, buf.length - 4);
+		return readUint32(buf, buf.length - 4);
 	}
 
 	void setChecksum(long checksum) {
-		ByteUtils.writeUint32(checksum, buf, buf.length - 4);
+		writeUint32(checksum, buf, buf.length - 4);
 	}
 
 	long calculateChecksum() {
@@ -38,11 +40,11 @@ abstract class Frame {
 	}
 
 	long getSequenceNumber() {
-		return ByteUtils.readUint32(buf, 1);
+		return readUint32(buf, 1);
 	}
 
 	void setSequenceNumber(long sequenceNumber) {
-		ByteUtils.writeUint32(sequenceNumber, buf, 1);
+		writeUint32(sequenceNumber, buf, 1);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/reliability/Receiver.java

@@ -101,6 +101,7 @@ class Receiver implements ReadHandler {
 		}
 	}
 
+	@SuppressWarnings("StatementWithEmptyBody")
 	private void handleData(byte[] b) throws IOException {
 		windowLock.lock();
 		try {
@@ -124,6 +125,7 @@ class Receiver implements ReadHandler {
 				finalSequenceNumber = sequenceNumber;
 				// Remove any data frames with higher sequence numbers
 				Iterator<Data> it = dataFrames.iterator();
+				//noinspection Java8CollectionRemoveIf
 				while (it.hasNext()) {
 					Data d1 = it.next();
 					if (d1.getSequenceNumber() >= finalSequenceNumber)
@@ -148,6 +150,7 @@ class Receiver implements ReadHandler {
 
 	private static class SequenceNumberComparator implements Comparator<Data> {
 
+		@SuppressWarnings("UseCompareMethod")
 		@Override
 		public int compare(Data d1, Data d2) {
 			long s1 = d1.getSequenceNumber(), s2 = d2.getSequenceNumber();

bramble-core/src/main/java/org/briarproject/bramble/reliability/ReceiverInputStream.java

@@ -8,6 +8,8 @@ import java.io.InputStream;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.lang.System.arraycopy;
+
 @NotThreadSafe
 @NotNullByDefault
 class ReceiverInputStream extends InputStream {
@@ -44,12 +46,13 @@ class ReceiverInputStream extends InputStream {
 		while (length == 0) if (!receive()) return -1;
 		if (data == null) throw new AssertionError();
 		len = Math.min(len, length);
-		System.arraycopy(data.getBuffer(), offset, b, off, len);
+		arraycopy(data.getBuffer(), offset, b, off, len);
 		offset += len;
 		length -= len;
 		return len;
 	}
 
+	@SuppressWarnings("BooleanMethodIsAlwaysInverted")
 	private boolean receive() throws IOException {
 		if (length != 0) throw new AssertionError();
 		if (data != null && data.isLastFrame()) {

bramble-core/src/main/java/org/briarproject/bramble/reliability/ReliabilityLayerImpl.java

@@ -16,6 +16,7 @@ import java.util.logging.Logger;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @MethodsNotNullByDefault
@@ -25,7 +26,7 @@ class ReliabilityLayerImpl implements ReliabilityLayer, WriteHandler {
 	private static final int TICK_INTERVAL = 500; // Milliseconds
 
 	private static final Logger LOG =
-			Logger.getLogger(ReliabilityLayerImpl.class.getName());
+			getLogger(ReliabilityLayerImpl.class.getName());
 
 	private final Executor executor;
 	private final Clock clock;

bramble-core/src/main/java/org/briarproject/bramble/reliability/Sender.java

@@ -16,6 +16,7 @@ import java.util.concurrent.locks.ReentrantLock;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 
 @ThreadSafe
 @NotNullByDefault
@@ -96,7 +97,7 @@ class Sender {
 			}
 			// If any older data frames are outstanding, retransmit the oldest
 			if (foundIndex > 0) {
-				fastRetransmit = outstanding.poll();
+				fastRetransmit = requireNonNull(outstanding.poll());
 				fastRetransmit.lastTransmitted = now;
 				fastRetransmit.retransmitted = true;
 				outstanding.add(fastRetransmit);
@@ -191,7 +192,7 @@ class Sender {
 		writeHandler.handleWrite(d.getBuffer());
 	}
 
-	void flush() throws IOException, InterruptedException {
+	void flush() throws InterruptedException {
 		windowLock.lock();
 		try {
 			while (dataWaiting || !outstanding.isEmpty())

bramble-core/src/main/java/org/briarproject/bramble/reliability/SenderOutputStream.java

@@ -7,6 +7,8 @@ import java.io.OutputStream;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.lang.System.arraycopy;
+
 @NotThreadSafe
 @NotNullByDefault
 class SenderOutputStream extends OutputStream {
@@ -59,20 +61,20 @@ class SenderOutputStream extends OutputStream {
 	public void write(byte[] b, int off, int len) throws IOException {
 		int available = Data.MAX_LENGTH - offset - Data.FOOTER_LENGTH;
 		while (available <= len) {
-			System.arraycopy(b, off, buf, offset, available);
+			arraycopy(b, off, buf, offset, available);
 			offset += available;
 			send(false);
 			off += available;
 			len -= available;
 			available = Data.MAX_LENGTH - offset - Data.FOOTER_LENGTH;
 		}
-		System.arraycopy(b, off, buf, offset, len);
+		arraycopy(b, off, buf, offset, len);
 		offset += len;
 	}
 
 	private void send(boolean lastFrame) throws IOException {
 		byte[] frame = new byte[offset + Data.FOOTER_LENGTH];
-		System.arraycopy(buf, 0, frame, 0, frame.length);
+		arraycopy(buf, 0, frame, 0, frame.length);
 		Data d = new Data(frame);
 		d.setLastFrame(lastFrame);
 		d.setSequenceNumber(sequenceNumber++);

bramble-core/src/main/java/org/briarproject/bramble/reliability/SlipDecoder.java

@@ -7,6 +7,8 @@ import java.io.IOException;
 
 import javax.annotation.concurrent.Immutable;
 
+import static java.lang.System.arraycopy;
+
 @Immutable
 @NotNullByDefault
 class SlipDecoder implements ReadHandler {
@@ -36,7 +38,7 @@ class SlipDecoder implements ReadHandler {
 				} else {
 					if (decodedLength > 0) {
 						byte[] decoded = new byte[decodedLength];
-						System.arraycopy(buf, 0, decoded, 0, decodedLength);
+						arraycopy(buf, 0, decoded, 0, decodedLength);
 						readHandler.handleRead(decoded);
 					}
 					reset(false);

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

@@ -1,7 +1,6 @@
 package org.briarproject.bramble.reporting;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.IoUtils;
 
 import java.io.Closeable;
 import java.io.File;
@@ -17,6 +16,9 @@ import java.util.concurrent.Semaphore;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
+import static java.io.File.createTempFile;
+import static org.briarproject.bramble.util.IoUtils.getInputStream;
+
 @Immutable
 @NotNullByDefault
 public class DevReportServer {
@@ -42,6 +44,7 @@ public class DevReportServer {
 		TokenBucket bucket = new TokenBucket();
 		bucket.start();
 		try {
+			//noinspection InfiniteLoopStatement
 			while (true) {
 				Socket s = ss.accept();
 				System.out.println("Incoming connection");
@@ -101,6 +104,7 @@ public class DevReportServer {
 		@Override
 		public void run() {
 			try {
+				//noinspection InfiniteLoopStatement
 				while (true) {
 					// If the bucket isn't full, add a token
 					if (semaphore.availablePermits() < MAX_TOKENS) {
@@ -131,9 +135,11 @@ public class DevReportServer {
 			OutputStream out = null;
 			try {
 				socket.setSoTimeout(SOCKET_TIMEOUT_MS);
-				in = IoUtils.getInputStream(socket);
+				in = getInputStream(socket);
+				// Directory may already exist
+				//noinspection ResultOfMethodCallIgnored
 				reportDir.mkdirs();
-				reportFile = File.createTempFile(FILE_PREFIX, FILE_SUFFIX,
+				reportFile = createTempFile(FILE_PREFIX, FILE_SUFFIX,
 						reportDir);
 				out = new FileOutputStream(reportFile);
 				System.out.println("Saving report to " + reportFile);
@@ -151,7 +157,8 @@ public class DevReportServer {
 				System.out.println("Saved " + length + " bytes");
 			} catch (IOException e) {
 				e.printStackTrace();
-				if (reportFile != null) reportFile.delete();
+				if (reportFile != null && !reportFile.delete())
+					System.err.println("Failed to delete report");
 			} finally {
 				tryToClose(in);
 				tryToClose(out);

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

@@ -9,8 +9,6 @@ import org.briarproject.bramble.api.plugin.TorConstants;
 import org.briarproject.bramble.api.plugin.event.TransportEnabledEvent;
 import org.briarproject.bramble.api.reporting.DevConfig;
 import org.briarproject.bramble.api.reporting.DevReporter;
-import org.briarproject.bramble.util.IoUtils;
-import org.briarproject.bramble.util.StringUtils;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -30,14 +28,18 @@ import javax.inject.Inject;
 import javax.net.SocketFactory;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.copyAndClose;
+import static org.briarproject.bramble.util.IoUtils.getOutputStream;
 import static org.briarproject.bramble.util.IoUtils.tryToClose;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 @Immutable
 @NotNullByDefault
 class DevReporterImpl implements DevReporter, EventListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(DevReporterImpl.class.getName());
+			getLogger(DevReporterImpl.class.getName());
 
 	private static final int SOCKET_TIMEOUT = 30 * 1000; // 30 seconds
 	private static final int LINE_LENGTH = 70;
@@ -73,7 +75,7 @@ class DevReporterImpl implements DevReporter, EventListener {
 	public void encryptReportToFile(File reportDir, String filename,
 			String report) throws FileNotFoundException {
 		LOG.info("Encrypting report to file");
-		byte[] plaintext = StringUtils.toUtf8(report);
+		byte[] plaintext = toUtf8(report);
 		byte[] ciphertext = crypto.encryptToKey(devConfig.getDevPublicKey(),
 				plaintext);
 		String armoured = crypto.asciiArmour(ciphertext, LINE_LENGTH);
@@ -109,17 +111,15 @@ class DevReporterImpl implements DevReporter, EventListener {
 		LOG.info("Sending reports to developers");
 		for (File f : reports) {
 			OutputStream out = null;
-			InputStream in = null;
 			try {
 				Socket s = connectToDevelopers();
-				out = IoUtils.getOutputStream(s);
-				in = new FileInputStream(f);
-				IoUtils.copyAndClose(in, out);
-				f.delete();
+				out = getOutputStream(s);
+				InputStream in = new FileInputStream(f);
+				copyAndClose(in, out);
+				if (!f.delete()) LOG.warning("Failed to delete report");
 			} catch (IOException e) {
 				LOG.log(WARNING, "Failed to send reports", e);
 				tryToClose(out, LOG, WARNING);
-				tryToClose(in, LOG, WARNING);
 				return;
 			}
 		}

bramble-core/src/main/java/org/briarproject/bramble/socks/SocksSocket.java

@@ -1,6 +1,5 @@
 package org.briarproject.bramble.socks;
 
-import org.briarproject.bramble.util.ByteUtils;
 import org.briarproject.bramble.util.IoUtils;
 
 import java.io.IOException;
@@ -12,6 +11,9 @@ import java.net.Socket;
 import java.net.SocketAddress;
 import java.util.Arrays;
 
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+import static org.briarproject.bramble.util.IoUtils.read;
+
 class SocksSocket extends Socket {
 
 	private static final String[] ERRORS = {
@@ -26,6 +28,7 @@ class SocksSocket extends Socket {
 			"Address type not supported"
 	};
 
+	@SuppressWarnings("MismatchedReadAndWriteOfArray")
 	private static final byte[] UNSPECIFIED_ADDRESS = new byte[4];
 
 	private final SocketAddress proxy;
@@ -88,7 +91,7 @@ class SocksSocket extends Socket {
 
 	private void receiveMethodResponse(InputStream in) throws IOException {
 		byte[] methodResponse = new byte[2];
-		IoUtils.read(in, methodResponse);
+		read(in, methodResponse);
 		byte version = methodResponse[0];
 		byte method = methodResponse[1];
 		if (version != 5)
@@ -108,14 +111,14 @@ class SocksSocket extends Socket {
 		connectRequest[4] = (byte) host.length(); // Length of domain name
 		for (int i = 0; i < host.length(); i++)
 			connectRequest[5 + i] = (byte) host.charAt(i);
-		ByteUtils.writeUint16(port, connectRequest, connectRequest.length - 2);
+		writeUint16(port, connectRequest, connectRequest.length - 2);
 		out.write(connectRequest);
 		out.flush();
 	}
 
 	private void receiveConnectResponse(InputStream in) throws IOException {
 		byte[] connectResponse = new byte[4];
-		IoUtils.read(in, connectResponse);
+		read(in, connectResponse);
 		int version = connectResponse[0] & 0xFF;
 		int reply = connectResponse[1] & 0xFF;
 		int addressType = connectResponse[3] & 0xFF;
@@ -126,9 +129,9 @@ class SocksSocket extends Socket {
 				throw new IOException("Connection failed: " + ERRORS[reply]);
 			else throw new IOException("Connection failed: " + reply);
 		}
-		if (addressType == 1) IoUtils.read(in, new byte[4]); // IPv4
-		else if (addressType == 4) IoUtils.read(in, new byte[16]); // IPv6
+		if (addressType == 1) read(in, new byte[4]); // IPv4
+		else if (addressType == 4) read(in, new byte[16]); // IPv6
 		else throw new IOException("Unsupported address type: " + addressType);
-		IoUtils.read(in, new byte[2]); // Port number
+		read(in, new byte[2]); // Port number
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/socks/SocksSocketFactory.java

@@ -45,7 +45,7 @@ class SocksSocketFactory extends SocketFactory {
 
 	@Override
 	public Socket createSocket(InetAddress address, int port,
-			InetAddress localAddress, int localPort) throws IOException {
+			InetAddress localAddress, int localPort) {
 		throw new UnsupportedOperationException();
 	}
 }

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

@@ -39,6 +39,7 @@ 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.api.lifecycle.LifecycleManager.LifecycleState.STOPPING;
 import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
@@ -55,7 +56,7 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 class DuplexOutgoingSession implements SyncSession, EventListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(DuplexOutgoingSession.class.getName());
+			getLogger(DuplexOutgoingSession.class.getName());
 
 	private static final ThrowingRunnable<IOException> CLOSE = () -> {
 	};

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

@@ -6,8 +6,6 @@ import org.briarproject.bramble.api.sync.ClientId;
 import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.GroupFactory;
 import org.briarproject.bramble.api.sync.GroupId;
-import org.briarproject.bramble.util.ByteUtils;
-import org.briarproject.bramble.util.StringUtils;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
@@ -15,6 +13,8 @@ import javax.inject.Inject;
 import static org.briarproject.bramble.api.sync.Group.FORMAT_VERSION;
 import static org.briarproject.bramble.api.sync.GroupId.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
@@ -33,10 +33,9 @@ class GroupFactoryImpl implements GroupFactory {
 	@Override
 	public Group createGroup(ClientId c, int majorVersion, byte[] descriptor) {
 		byte[] majorVersionBytes = new byte[INT_32_BYTES];
-		ByteUtils.writeUint32(majorVersion, majorVersionBytes, 0);
+		writeUint32(majorVersion, majorVersionBytes, 0);
 		byte[] hash = crypto.hash(LABEL, FORMAT_VERSION_BYTES,
-				StringUtils.toUtf8(c.getString()), majorVersionBytes,
-				descriptor);
+				toUtf8(c.getString()), majorVersionBytes, descriptor);
 		return new Group(new GroupId(hash), c, majorVersion, descriptor);
 	}
 }

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

@@ -26,6 +26,7 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.STOPPING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
@@ -37,7 +38,7 @@ import static org.briarproject.bramble.util.LogUtils.logException;
 class IncomingSession implements SyncSession, EventListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(IncomingSession.class.getName());
+			getLogger(IncomingSession.class.getName());
 
 	private final DatabaseComponent db;
 	private final Executor dbExecutor;

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

@@ -7,11 +7,11 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.util.ByteUtils;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
+import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.sync.Message.FORMAT_VERSION;
 import static org.briarproject.bramble.api.sync.MessageId.BLOCK_LABEL;
 import static org.briarproject.bramble.api.sync.MessageId.ID_LABEL;
@@ -19,6 +19,8 @@ import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_L
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
+import static org.briarproject.bramble.util.ByteUtils.readUint64;
+import static org.briarproject.bramble.util.ByteUtils.writeUint64;
 
 @Immutable
 @NotNullByDefault
@@ -47,7 +49,7 @@ class MessageFactoryImpl implements MessageFactory {
 		// There's only one block, so the root hash is the hash of the block
 		byte[] rootHash = crypto.hash(BLOCK_LABEL, FORMAT_VERSION_BYTES, body);
 		byte[] timeBytes = new byte[INT_64_BYTES];
-		ByteUtils.writeUint64(timestamp, timeBytes, 0);
+		writeUint64(timestamp, timeBytes, 0);
 		byte[] idHash = crypto.hash(ID_LABEL, FORMAT_VERSION_BYTES,
 				g.getBytes(), timeBytes, rootHash);
 		return new MessageId(idHash);
@@ -60,11 +62,11 @@ class MessageFactoryImpl implements MessageFactory {
 		if (raw.length > MAX_MESSAGE_LENGTH)
 			throw new IllegalArgumentException();
 		byte[] groupId = new byte[UniqueId.LENGTH];
-		System.arraycopy(raw, 0, groupId, 0, UniqueId.LENGTH);
+		arraycopy(raw, 0, groupId, 0, UniqueId.LENGTH);
 		GroupId g = new GroupId(groupId);
-		long timestamp = ByteUtils.readUint64(raw, UniqueId.LENGTH);
+		long timestamp = readUint64(raw, UniqueId.LENGTH);
 		byte[] body = new byte[raw.length - MESSAGE_HEADER_LENGTH];
-		System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
+		arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
 		MessageId id = getMessageId(g, timestamp, body);
 		return new Message(id, g, timestamp, body);
 	}
@@ -73,9 +75,9 @@ class MessageFactoryImpl implements MessageFactory {
 	public byte[] getRawMessage(Message m) {
 		byte[] body = m.getBody();
 		byte[] raw = new byte[MESSAGE_HEADER_LENGTH + body.length];
-		System.arraycopy(m.getGroupId().getBytes(), 0, raw, 0, UniqueId.LENGTH);
-		ByteUtils.writeUint64(m.getTimestamp(), raw, UniqueId.LENGTH);
-		System.arraycopy(body, 0, raw, MESSAGE_HEADER_LENGTH, body.length);
+		arraycopy(m.getGroupId().getBytes(), 0, raw, 0, UniqueId.LENGTH);
+		writeUint64(m.getTimestamp(), raw, UniqueId.LENGTH);
+		arraycopy(body, 0, raw, MESSAGE_HEADER_LENGTH, body.length);
 		return raw;
 	}
 }