Merge branch '346-smaller-qr-codes' into 'master'

Encode transport properties more compactly in QR codes

The [original BQP spec](https://code.briarproject.org/akwizgran/briar/wikis/BQP) described a compact encoding for transport properties, with the goal of making the QR code as small as possible. At some point during the implementation, I asked @str4d to use TransportIds and TransportProperties instead, as described in the [current spec](https://code.briarproject.org/akwizgran/briar-spec/blob/master/protocols/BQP.md). That was a mistake.

Using the original format reduces the payload from 60 to 34 bytes (43% smaller) for Bluetooth only, and from 96 to 49 bytes (49% smaller) for Bluetooth and LAN. This makes it easier to scan codes from low-resolution screens using fixed-focus and/or low-resolution cameras. Using this branch I can exchange codes between the Sony Xperia Tipo (320x480 screen, fixed focus, 640x480 preview size) and the Huawei Ascend Y300 (480x800 screen, infinity focus, 1280x720 preview size).

This also removes an obstacle to implementing #558, as TransportIds are no longer included in QR codes.

Closes #346.

See merge request !394

briar-android/src/org/briarproject/android/keyagreement/ShowQrCodeFragment.java

@@ -57,6 +57,7 @@ import static android.content.pm.ActivityInfo.SCREEN_ORIENTATION_NOSENSOR;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
 import static android.widget.Toast.LENGTH_LONG;
+import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 
 public class ShowQrCodeFragment extends BaseEventFragment
@@ -244,8 +245,10 @@ public class ShowQrCodeFragment extends BaseEventFragment
 	@UiThread
 	private void qrCodeScanned(String content) {
 		try {
-			Payload remotePayload = payloadParser.parse(
+			byte[] encoded = Base64.decode(content, 0);
-					Base64.decode(content, 0));
+			if (LOG.isLoggable(INFO))
+				LOG.info("Remote payload is " + encoded.length + " bytes");
+			Payload remotePayload = payloadParser.parse(encoded);
 			cameraView.setVisibility(INVISIBLE);
 			statusView.setVisibility(VISIBLE);
 			status.setText(R.string.connecting_to_device);
@@ -293,9 +296,10 @@ public class ShowQrCodeFragment extends BaseEventFragment
 
 			@Override
 			protected Bitmap doInBackground(Void... params) {
-				String input =
+				byte[] encoded = payloadEncoder.encode(payload);
-						Base64.encodeToString(payloadEncoder.encode(payload),
+				if (LOG.isLoggable(INFO))
-								0);
+					LOG.info("Local payload is " + encoded.length + " bytes");
+				String input = Base64.encodeToString(encoded, 0);
 				return QrCodeUtils.createQrCode(dm, input);
 			}
 

briar-android/src/org/briarproject/plugins/droidtooth/DroidtoothPlugin.java

@@ -11,12 +11,15 @@ import android.content.IntentFilter;
 
 import org.briarproject.android.api.AndroidExecutor;
 import org.briarproject.android.util.AndroidUtils;
+import org.briarproject.api.FormatException;
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
@@ -24,6 +27,7 @@ import org.briarproject.api.plugins.duplex.DuplexTransportConnection;
 import org.briarproject.api.properties.TransportProperties;
 import org.briarproject.util.StringUtils;
 
+import java.io.Closeable;
 import java.io.IOException;
 import java.io.InputStream;
 import java.security.SecureRandom;
@@ -44,6 +48,8 @@ import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
+
 import static android.bluetooth.BluetoothAdapter.ACTION_SCAN_MODE_CHANGED;
 import static android.bluetooth.BluetoothAdapter.ACTION_STATE_CHANGED;
 import static android.bluetooth.BluetoothAdapter.EXTRA_SCAN_MODE;
@@ -57,8 +63,11 @@ import static android.bluetooth.BluetoothDevice.EXTRA_DEVICE;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_BLUETOOTH;
 import static org.briarproject.util.PrivacyUtils.scrubMacAddress;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 class DroidtoothPlugin implements DuplexPlugin {
 
 	// Share an ID with the J2SE Bluetooth plugin
@@ -217,7 +226,7 @@ class DroidtoothPlugin implements DuplexPlugin {
 		return UUID.fromString(uuid);
 	}
 
-	private void tryToClose(BluetoothServerSocket ss) {
+	private void tryToClose(@Nullable BluetoothServerSocket ss) {
 		try {
 			if (ss != null) ss.close();
 		} catch (IOException e) {
@@ -340,9 +349,9 @@ class DroidtoothPlugin implements DuplexPlugin {
 		}
 	}
 
-	private void tryToClose(BluetoothSocket s) {
+	private void tryToClose(@Nullable Closeable c) {
 		try {
-			if (s != null) s.close();
+			if (c != null) c.close();
 		} catch (IOException e) {
 			if (LOG.isLoggable(WARNING)) LOG.log(WARNING, e.toString(), e);
 		}
@@ -420,7 +429,7 @@ class DroidtoothPlugin implements DuplexPlugin {
 	}
 
 	private void closeSockets(final List<Future<BluetoothSocket>> futures,
-			final BluetoothSocket chosen) {
+			@Nullable final BluetoothSocket chosen) {
 		ioExecutor.execute(new Runnable() {
 			@Override
 			public void run() {
@@ -454,6 +463,9 @@ class DroidtoothPlugin implements DuplexPlugin {
 	@Override
 	public KeyAgreementListener createKeyAgreementListener(byte[] commitment) {
 		if (!isRunning()) return null;
+		// There's no point listening if we can't discover our own address
+		String address = AndroidUtils.getBluetoothAddress(appContext, adapter);
+		if (address.isEmpty()) return null;
 		// No truncation necessary because COMMIT_LENGTH = 16
 		UUID uuid = UUID.nameUUIDFromBytes(commitment);
 		if (LOG.isLoggable(INFO)) LOG.info("Key agreement UUID " + uuid);
@@ -466,23 +478,23 @@ class DroidtoothPlugin implements DuplexPlugin {
 			if (LOG.isLoggable(WARNING)) LOG.log(WARNING, e.toString(), e);
 			return null;
 		}
-		TransportProperties p = new TransportProperties();
+		BdfList descriptor = new BdfList();
-		String address = AndroidUtils.getBluetoothAddress(appContext, adapter);
+		descriptor.add(TRANSPORT_ID_BLUETOOTH);
-		if (!StringUtils.isNullOrEmpty(address))
+		descriptor.add(StringUtils.macToBytes(address));
-			p.put(PROP_ADDRESS, address);
+		return new BluetoothKeyAgreementListener(descriptor, ss);
-		TransportDescriptor d = new TransportDescriptor(ID, p);
-		return new BluetoothKeyAgreementListener(d, ss);
 	}
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		if (!isRunning()) return null;
-		if (!ID.equals(d.getIdentifier())) return null;
+		String address;
-		TransportProperties p = d.getProperties();
+		try {
-		if (p == null) return null;
+			address = parseAddress(descriptor);
-		String address = p.get(PROP_ADDRESS);
+		} catch (FormatException e) {
-		if (StringUtils.isNullOrEmpty(address)) return null;
+			LOG.info("Invalid address in key agreement descriptor");
+			return null;
+		}
 		// No truncation necessary because COMMIT_LENGTH = 16
 		UUID uuid = UUID.nameUUIDFromBytes(commitment);
 		if (LOG.isLoggable(INFO))
@@ -492,6 +504,12 @@ class DroidtoothPlugin implements DuplexPlugin {
 		return new DroidtoothTransportConnection(this, s);
 	}
 
+	private String parseAddress(BdfList descriptor) throws FormatException {
+		byte[] mac = descriptor.getRaw(1);
+		if (mac.length != 6) throw new FormatException();
+		return StringUtils.macToString(mac);
+	}
+
 	private class BluetoothStateReceiver extends BroadcastReceiver {
 
 		@Override
@@ -626,7 +644,7 @@ class DroidtoothPlugin implements DuplexPlugin {
 
 		private final BluetoothServerSocket ss;
 
-		BluetoothKeyAgreementListener(TransportDescriptor descriptor,
+		BluetoothKeyAgreementListener(BdfList descriptor,
 				BluetoothServerSocket ss) {
 			super(descriptor);
 			this.ss = ss;

briar-android/src/org/briarproject/plugins/tcp/AndroidLanTcpPlugin.java

@@ -7,16 +7,20 @@ import android.content.IntentFilter;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
 
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
+
 import static android.content.Context.CONNECTIVITY_SERVICE;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.TYPE_WIFI;
 
+@NotNullByDefault
 class AndroidLanTcpPlugin extends LanTcpPlugin {
 
 	private static final Logger LOG =
@@ -24,6 +28,7 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 
 	private final Context appContext;
 
+	@Nullable
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	AndroidLanTcpPlugin(Executor ioExecutor, Backoff backoff,

briar-android/src/org/briarproject/plugins/tor/TorPlugin.java

@@ -19,11 +19,12 @@ import org.briarproject.android.util.AndroidUtils;
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.event.Event;
 import org.briarproject.api.event.EventListener;
 import org.briarproject.api.event.SettingsUpdatedEvent;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.TorConstants;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
@@ -60,6 +61,7 @@ import java.util.logging.Logger;
 import java.util.regex.Pattern;
 import java.util.zip.ZipInputStream;
 
+import javax.annotation.Nullable;
 import javax.net.SocketFactory;
 
 import static android.content.Context.CONNECTIVITY_SERVICE;
@@ -76,6 +78,7 @@ import static net.freehaven.tor.control.TorControlCommands.HS_PRIVKEY;
 import static org.briarproject.api.plugins.TorConstants.CONTROL_PORT;
 import static org.briarproject.util.PrivacyUtils.scrubOnion;
 
+@NotNullByDefault
 class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	private static final String PROP_ONION = "onion";
@@ -104,9 +107,13 @@ class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
 	private volatile boolean running = false;
+	@Nullable
 	private volatile ServerSocket socket = null;
+	@Nullable
 	private volatile Socket controlSocket = null;
+	@Nullable
 	private volatile TorControlConnection controlConnection = null;
+	@Nullable
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	TorPlugin(Executor ioExecutor, Context appContext,
@@ -289,7 +296,7 @@ class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		return appContext.getResources().getAssets().open("torrc");
 	}
 
-	private void tryToClose(Closeable c) {
+	private void tryToClose(@Nullable Closeable c) {
 		try {
 			if (c != null) c.close();
 		} catch (IOException e) {
@@ -297,7 +304,7 @@ class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		}
 	}
 
-	private void tryToClose(Socket s) {
+	private void tryToClose(@Nullable Socket s) {
 		try {
 			if (s != null) s.close();
 		} catch (IOException e) {
@@ -385,7 +392,7 @@ class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		});
 	}
 
-	private void tryToClose(ServerSocket ss) {
+	private void tryToClose(@Nullable ServerSocket ss) {
 		try {
 			if (ss != null) ss.close();
 		} catch (IOException e) {
@@ -574,7 +581,7 @@ class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		throw new UnsupportedOperationException();
 	}
 

briar-api/src/org/briarproject/api/keyagreement/KeyAgreementConstants.java

@@ -4,7 +4,7 @@ package org.briarproject.api.keyagreement;
 public interface KeyAgreementConstants {
 
 	/** The current version of the BQP protocol. */
-	byte PROTOCOL_VERSION = 1;
+	byte PROTOCOL_VERSION = 2;
 
 	/** The length of the record header in bytes. */
 	int RECORD_HEADER_LENGTH = 4;
@@ -16,4 +16,10 @@ public interface KeyAgreementConstants {
 	int COMMIT_LENGTH = 16;
 
 	long CONNECTION_TIMEOUT = 20 * 1000; // Milliseconds
+
+	/** The transport identifier for Bluetooth. */
+	int TRANSPORT_ID_BLUETOOTH = 0;
+
+	/** The transport identifier for LAN. */
+	int TRANSPORT_ID_LAN = 1;
 }

briar-api/src/org/briarproject/api/keyagreement/KeyAgreementListener.java

@@ -1,5 +1,7 @@
 package org.briarproject.api.keyagreement;
 
+import org.briarproject.api.data.BdfList;
+
 import java.util.concurrent.Callable;
 
 /**
@@ -7,9 +9,9 @@ import java.util.concurrent.Callable;
  */
 public abstract class KeyAgreementListener {
 
-	private final TransportDescriptor descriptor;
+	private final BdfList descriptor;
 
-	public KeyAgreementListener(TransportDescriptor descriptor) {
+	public KeyAgreementListener(BdfList descriptor) {
 		this.descriptor = descriptor;
 	}
 
@@ -17,7 +19,7 @@ public abstract class KeyAgreementListener {
 	 * Returns the descriptor that a remote peer can use to connect to this
 	 * listener.
 	 */
-	public TransportDescriptor getDescriptor() {
+	public BdfList getDescriptor() {
 		return descriptor;
 	}
 

briar-api/src/org/briarproject/api/keyagreement/Payload.java

@@ -1,29 +1,40 @@
 package org.briarproject.api.keyagreement;
 
 import org.briarproject.api.Bytes;
+import org.briarproject.api.TransportId;
+import org.briarproject.api.data.BdfList;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 
-import java.util.List;
+import java.util.Map;
+
+import javax.annotation.concurrent.Immutable;
 
 /**
  * A BQP payload.
  */
+@Immutable
+@NotNullByDefault
 public class Payload implements Comparable<Payload> {
 
 	private final Bytes commitment;
-	private final List<TransportDescriptor> descriptors;
+	private final Map<TransportId, BdfList> descriptors;
 
-	public Payload(byte[] commitment, List<TransportDescriptor> descriptors) {
+	public Payload(byte[] commitment, Map<TransportId, BdfList> descriptors) {
 		this.commitment = new Bytes(commitment);
 		this.descriptors = descriptors;
 	}
 
-	/** Returns the commitment contained in this payload. */
+	/**
+	 * Returns the commitment contained in this payload.
+	 */
 	public byte[] getCommitment() {
 		return commitment.getBytes();
 	}
 
-	/** Returns the transport descriptors contained in this payload. */
+	/**
-	public List<TransportDescriptor> getTransportDescriptors() {
+	 * Returns the transport descriptors contained in this payload.
+	 */
+	public Map<TransportId, BdfList> getTransportDescriptors() {
 		return descriptors;
 	}
 

briar-api/src/org/briarproject/api/keyagreement/PayloadParser.java

@@ -1,7 +1,10 @@
 package org.briarproject.api.keyagreement;
 
+import org.briarproject.api.nullsafety.NotNullByDefault;
+
 import java.io.IOException;
 
+@NotNullByDefault
 public interface PayloadParser {
 
 	Payload parse(byte[] raw) throws IOException;

briar-api/src/org/briarproject/api/keyagreement/TransportDescriptor.java

@@ -1,28 +0,0 @@
-package org.briarproject.api.keyagreement;
-
-import org.briarproject.api.TransportId;
-import org.briarproject.api.properties.TransportProperties;
-
-/**
- * Describes how to connect to a device over a short-range transport.
- */
-public class TransportDescriptor {
-
-	private final TransportId id;
-	private final TransportProperties properties;
-
-	public TransportDescriptor(TransportId id, TransportProperties properties) {
-		this.id = id;
-		this.properties = properties;
-	}
-
-	/** Returns the transport identifier. */
-	public TransportId getIdentifier() {
-		return id;
-	}
-
-	/** Returns the transport properties. */
-	public TransportProperties getProperties() {
-		return properties;
-	}
-}

briar-api/src/org/briarproject/api/plugins/Plugin.java

@@ -2,28 +2,42 @@ package org.briarproject.api.plugins;
 
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 
 import java.io.IOException;
 import java.util.Collection;
 
+@NotNullByDefault
 public interface Plugin {
 
-	/** Returns the plugin's transport identifier. */
+	/**
+	 * Returns the plugin's transport identifier.
+	 */
 	TransportId getId();
 
-	/** Returns the transport's maximum latency in milliseconds. */
+	/**
+	 * Returns the transport's maximum latency in milliseconds.
+	 */
 	int getMaxLatency();
 
-	/** Returns the transport's maximum idle time in milliseconds. */
+	/**
+	 * Returns the transport's maximum idle time in milliseconds.
+	 */
 	int getMaxIdleTime();
 
-	/** Starts the plugin and returns true if it started successfully. */
+	/**
+	 * Starts the plugin and returns true if it started successfully.
+	 */
 	boolean start() throws IOException;
 
-	/** Stops the plugin. */
+	/**
+	 * Stops the plugin.
+	 */
 	void stop() throws IOException;
 
-	/** Returns true if the plugin is running. */
+	/**
+	 * Returns true if the plugin is running.
+	 */
 	boolean isRunning();
 
 	/**

briar-api/src/org/briarproject/api/plugins/PluginManager.java

@@ -1,21 +1,26 @@
 package org.briarproject.api.plugins;
 
 import org.briarproject.api.TransportId;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.simplex.SimplexPlugin;
 
 import java.util.Collection;
 
+import javax.annotation.Nullable;
+
 /**
  * Responsible for starting transport plugins at startup and stopping them at
  * shutdown.
  */
+@NotNullByDefault
 public interface PluginManager {
 
 	/**
 	 * Returns the plugin for the given transport, or null if no such plugin
 	 * has been created.
 	 */
+	@Nullable
 	Plugin getPlugin(TransportId t);
 
 	/**

briar-api/src/org/briarproject/api/plugins/duplex/DuplexPlugin.java

@@ -2,21 +2,30 @@ package org.briarproject.api.plugins.duplex;
 
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.Plugin;
 
-/** An interface for transport plugins that support duplex communication. */
+import javax.annotation.Nullable;
+
+/**
+ * An interface for transport plugins that support duplex communication.
+ */
+@NotNullByDefault
 public interface DuplexPlugin extends Plugin {
 
 	/**
 	 * Attempts to create and return a connection to the given contact using
 	 * the current transport and configuration properties. Returns null if a
-	 * connection could not be created.
+	 * connection cannot be created.
 	 */
+	@Nullable
 	DuplexTransportConnection createConnection(ContactId c);
 
-	/** Returns true if the plugin supports exchanging invitations. */
+	/**
+	 * Returns true if the plugin supports exchanging invitations.
+	 */
 	boolean supportsInvitations();
 
 	/**
@@ -24,21 +33,27 @@ public interface DuplexPlugin extends Plugin {
 	 * peer. Returns null if no connection can be established within the given
 	 * time.
 	 */
+	@Nullable
 	DuplexTransportConnection createInvitationConnection(PseudoRandom r,
 			long timeout, boolean alice);
 
-	/** Returns true if the plugin supports short-range key agreement. */
+	/**
+	 * Returns true if the plugin supports short-range key agreement.
+	 */
 	boolean supportsKeyAgreement();
 
 	/**
-	 * Returns a listener that can be used to perform key agreement.
+	 * Attempts to create and return a listener that can be used to perform key
+	 * agreement. Returns null if a listener cannot be created.
 	 */
+	@Nullable
 	KeyAgreementListener createKeyAgreementListener(byte[] localCommitment);
 
 	/**
 	 * Attempts to connect to the remote peer specified in the given descriptor.
 	 * Returns null if no connection can be established within the given time.
 	 */
+	@Nullable
 	DuplexTransportConnection createKeyAgreementConnection(
-			byte[] remoteCommitment, TransportDescriptor d, long timeout);
+			byte[] remoteCommitment, BdfList descriptor, long timeout);
 }

briar-api/src/org/briarproject/api/plugins/simplex/SimplexPlugin.java

@@ -1,24 +1,32 @@
 package org.briarproject.api.plugins.simplex;
 
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.Plugin;
 import org.briarproject.api.plugins.TransportConnectionReader;
 import org.briarproject.api.plugins.TransportConnectionWriter;
 
-/** An interface for transport plugins that support simplex communication. */
+import javax.annotation.Nullable;
+
+/**
+ * An interface for transport plugins that support simplex communication.
+ */
+@NotNullByDefault
 public interface SimplexPlugin extends Plugin {
 
 	/**
 	 * Attempts to create and return a reader for the given contact using the
 	 * current transport and configuration properties. Returns null if a reader
-	 * could not be created.
+	 * cannot be created.
 	 */
+	@Nullable
 	TransportConnectionReader createReader(ContactId c);
 
 	/**
 	 * Attempts to create and return a writer for the given contact using the
 	 * current transport and configuration properties. Returns null if a writer
-	 * could not be created.
+	 * cannot be created.
 	 */
+	@Nullable
 	TransportConnectionWriter createWriter(ContactId c);
 }

briar-core/src/org/briarproject/keyagreement/KeyAgreementConnector.java

@@ -1,11 +1,13 @@
 package org.briarproject.keyagreement;
 
+import org.briarproject.api.TransportId;
 import org.briarproject.api.crypto.CryptoComponent;
 import org.briarproject.api.crypto.KeyPair;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
 import org.briarproject.api.keyagreement.Payload;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.plugins.Plugin;
 import org.briarproject.api.plugins.PluginManager;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexTransportConnection;
@@ -14,7 +16,10 @@ import org.briarproject.api.system.Clock;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CompletionService;
 import java.util.concurrent.ExecutionException;
@@ -68,14 +73,13 @@ class KeyAgreementConnector {
 		byte[] commitment = crypto.deriveKeyCommitment(
 				localKeyPair.getPublic().getEncoded());
 		// Start all listeners and collect their descriptors
-		List<TransportDescriptor> descriptors =
+		Map<TransportId, BdfList> descriptors =
-				new ArrayList<TransportDescriptor>();
+				new HashMap<TransportId, BdfList>();
 		for (DuplexPlugin plugin : pluginManager.getKeyAgreementPlugins()) {
-			KeyAgreementListener l = plugin.createKeyAgreementListener(
+			KeyAgreementListener l =
-					commitment);
+					plugin.createKeyAgreementListener(commitment);
 			if (l != null) {
-				TransportDescriptor d = l.getDescriptor();
+				descriptors.put(plugin.getId(), l.getDescriptor());
-				descriptors.add(d);
 				pending.add(connect.submit(new ReadableTask(l.listen())));
 				listeners.add(l);
 			}
@@ -100,13 +104,16 @@ class KeyAgreementConnector {
 
 		// Start connecting over supported transports
 		LOG.info("Starting outgoing BQP connections");
-		for (TransportDescriptor d : remotePayload.getTransportDescriptors()) {
+		Map<TransportId, BdfList> descriptors =
-			DuplexPlugin plugin = (DuplexPlugin) pluginManager.getPlugin(
+				remotePayload.getTransportDescriptors();
-					d.getIdentifier());
+		for (Entry<TransportId, BdfList> e : descriptors.entrySet()) {
-			if (plugin != null)
+			Plugin p = pluginManager.getPlugin(e.getKey());
+			if (p instanceof DuplexPlugin) {
+				DuplexPlugin plugin = (DuplexPlugin) p;
 				pending.add(connect.submit(new ReadableTask(
 						new ConnectorTask(plugin, remotePayload.getCommitment(),
-								d, end))));
+								e.getValue(), end))));
+			}
 		}
 
 		// Get chosen connection
@@ -170,12 +177,12 @@ class KeyAgreementConnector {
 	private class ConnectorTask implements Callable<KeyAgreementConnection> {
 
 		private final byte[] commitment;
-		private final TransportDescriptor descriptor;
+		private final BdfList descriptor;
 		private final long end;
 		private final DuplexPlugin plugin;
 
 		private ConnectorTask(DuplexPlugin plugin, byte[] commitment,
-				TransportDescriptor descriptor, long end) {
+				BdfList descriptor, long end) {
 			this.plugin = plugin;
 			this.commitment = commitment;
 			this.descriptor = descriptor;

briar-core/src/org/briarproject/keyagreement/PayloadEncoderImpl.java

@@ -1,24 +1,30 @@
 package org.briarproject.keyagreement;
 
+import org.briarproject.api.TransportId;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.data.BdfWriter;
 import org.briarproject.api.data.BdfWriterFactory;
 import org.briarproject.api.keyagreement.Payload;
 import org.briarproject.api.keyagreement.PayloadEncoder;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.util.Map;
 
+import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static org.briarproject.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
 
+@Immutable
+@NotNullByDefault
 class PayloadEncoderImpl implements PayloadEncoder {
 
 	private final BdfWriterFactory bdfWriterFactory;
 
 	@Inject
-	public PayloadEncoderImpl(BdfWriterFactory bdfWriterFactory) {
+	PayloadEncoderImpl(BdfWriterFactory bdfWriterFactory) {
 		this.bdfWriterFactory = bdfWriterFactory;
 	}
 
@@ -30,18 +36,13 @@ class PayloadEncoderImpl implements PayloadEncoder {
 			w.writeListStart(); // Payload start
 			w.writeLong(PROTOCOL_VERSION);
 			w.writeRaw(p.getCommitment());
-			w.writeListStart(); // Descriptors start
+			Map<TransportId, BdfList> descriptors = p.getTransportDescriptors();
-			for (TransportDescriptor d : p.getTransportDescriptors()) {
+			for (BdfList descriptor : descriptors.values())
-				w.writeListStart();
+				w.writeList(descriptor);
-				w.writeString(d.getIdentifier().getString());
-				w.writeDictionary(d.getProperties());
-				w.writeListEnd();
-			}
-			w.writeListEnd(); // Descriptors end
 			w.writeListEnd(); // Payload end
 		} catch (IOException e) {
 			// Shouldn't happen with ByteArrayOutputStream
-			throw new RuntimeException(e);
+			throw new AssertionError(e);
 		}
 		return out.toByteArray();
 	}

briar-core/src/org/briarproject/keyagreement/PayloadParserImpl.java

@@ -2,30 +2,34 @@ package org.briarproject.keyagreement;
 
 import org.briarproject.api.FormatException;
 import org.briarproject.api.TransportId;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.data.BdfReader;
 import org.briarproject.api.data.BdfReaderFactory;
 import org.briarproject.api.keyagreement.Payload;
 import org.briarproject.api.keyagreement.PayloadParser;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.NotNullByDefault;
-import org.briarproject.api.properties.TransportProperties;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
-import java.util.ArrayList;
+import java.util.HashMap;
-import java.util.List;
+import java.util.Map;
 
+import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static org.briarproject.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
 import static org.briarproject.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
-import static org.briarproject.api.properties.TransportPropertyConstants.MAX_PROPERTY_LENGTH;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_BLUETOOTH;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
 
+@Immutable
+@NotNullByDefault
 class PayloadParserImpl implements PayloadParser {
 
 	private final BdfReaderFactory bdfReaderFactory;
 
 	@Inject
-	public PayloadParserImpl(BdfReaderFactory bdfReaderFactory) {
+	PayloadParserImpl(BdfReaderFactory bdfReaderFactory) {
 		this.bdfReaderFactory = bdfReaderFactory;
 	}
 
@@ -33,36 +37,28 @@ class PayloadParserImpl implements PayloadParser {
 	public Payload parse(byte[] raw) throws IOException {
 		ByteArrayInputStream in = new ByteArrayInputStream(raw);
 		BdfReader r = bdfReaderFactory.createReader(in);
-		r.readListStart(); // Payload start
+		// The payload is a BDF list with two or more elements
-		int proto = (int) r.readLong();
+		BdfList payload = r.readList();
-		if (proto != PROTOCOL_VERSION)
+		if (payload.size() < 2) throw new FormatException();
-			throw new FormatException();
+		if (!r.eof()) throw new FormatException();
-		byte[] commitment = r.readRaw(COMMIT_LENGTH);
+		// First element: the protocol version
-		if (commitment.length != COMMIT_LENGTH)
+		long protocolVersion = payload.getLong(0);
-			throw new FormatException();
+		if (protocolVersion != PROTOCOL_VERSION) throw new FormatException();
-		List<TransportDescriptor> descriptors = new ArrayList<TransportDescriptor>();
+		// Second element: the public key commitment
-		r.readListStart(); // Descriptors start
+		byte[] commitment = payload.getRaw(1);
-		while (r.hasList()) {
+		if (commitment.length != COMMIT_LENGTH) throw new FormatException();
-			r.readListStart();
+		// Remaining elements: transport descriptors
-			while (!r.hasListEnd()) {
+		Map<TransportId, BdfList> recognised =
-				TransportId id =
+				new HashMap<TransportId, BdfList>();
-						new TransportId(r.readString(MAX_PROPERTY_LENGTH));
+		for (int i = 2; i < payload.size(); i++) {
-				TransportProperties p = new TransportProperties();
+			BdfList descriptor = payload.getList(i);
-				r.readDictionaryStart();
+			long transportId = descriptor.getLong(0);
-				while (!r.hasDictionaryEnd()) {
+			if (transportId == TRANSPORT_ID_BLUETOOTH) {
-					String key = r.readString(MAX_PROPERTY_LENGTH);
+				recognised.put(new TransportId("bt"), descriptor);
-					String value = r.readString(MAX_PROPERTY_LENGTH);
+			} else if (transportId == TRANSPORT_ID_LAN) {
-					p.put(key, value);
+				recognised.put(new TransportId("lan"), descriptor);
-				}
-				r.readDictionaryEnd();
-				descriptors.add(new TransportDescriptor(id, p));
 			}
-			r.readListEnd();
 		}
-		r.readListEnd(); // Descriptors end
+		return new Payload(commitment, recognised);
-		r.readListEnd(); // Payload end
-		if (!r.eof())
-			throw new FormatException();
-		return new Payload(commitment, descriptors);
 	}
 }

briar-core/src/org/briarproject/plugins/PluginManagerImpl.java

@@ -9,6 +9,7 @@ import org.briarproject.api.event.TransportEnabledEvent;
 import org.briarproject.api.lifecycle.IoExecutor;
 import org.briarproject.api.lifecycle.Service;
 import org.briarproject.api.lifecycle.ServiceException;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.ConnectionManager;
 import org.briarproject.api.plugins.Plugin;
 import org.briarproject.api.plugins.PluginCallback;
@@ -42,11 +43,14 @@ import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 
+@ThreadSafe
+@NotNullByDefault
 class PluginManagerImpl implements PluginManager, Service {
 
 	private static final Logger LOG =

briar-core/src/org/briarproject/plugins/file/FilePlugin.java

@@ -1,6 +1,7 @@
 package org.briarproject.plugins.file;
 
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.TransportConnectionReader;
 import org.briarproject.api.plugins.TransportConnectionWriter;
 import org.briarproject.api.plugins.simplex.SimplexPlugin;
@@ -17,10 +18,13 @@ import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
+
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.api.transport.TransportConstants.MIN_STREAM_LENGTH;
 
-public abstract class FilePlugin implements SimplexPlugin {
+@NotNullByDefault
+abstract class FilePlugin implements SimplexPlugin {
 
 	private static final Logger LOG =
 			Logger.getLogger(FilePlugin.class.getName());
@@ -32,6 +36,7 @@ public abstract class FilePlugin implements SimplexPlugin {
 
 	protected volatile boolean running = false;
 
+	@Nullable
 	protected abstract File chooseOutputDirectory();
 	protected abstract Collection<File> findFilesByName(String filename);
 	protected abstract void writerFinished(File f);
@@ -82,6 +87,7 @@ public abstract class FilePlugin implements SimplexPlugin {
 		return filename.toLowerCase(Locale.US).matches("[a-z]{8}\\.dat");
 	}
 
+	@Nullable
 	private TransportConnectionWriter createWriter(String filename) {
 		if (!running) return null;
 		File dir = chooseOutputDirectory();

briar-core/src/org/briarproject/plugins/tcp/LanTcpPlugin.java

@@ -1,10 +1,12 @@
 package org.briarproject.plugins.tcp;
 
+import org.briarproject.api.FormatException;
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
 import org.briarproject.api.plugins.duplex.DuplexTransportConnection;
@@ -19,6 +21,7 @@ import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.net.SocketAddress;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedList;
@@ -29,8 +32,11 @@ import java.util.logging.Logger;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
+import static org.briarproject.util.ByteUtils.MAX_16_BIT_UNSIGNED;
 import static org.briarproject.util.PrivacyUtils.scrubSocketAddress;
 
+@NotNullByDefault
 class LanTcpPlugin extends TcpPlugin {
 
 	static final TransportId ID = new TransportId("lan");
@@ -40,7 +46,6 @@ class LanTcpPlugin extends TcpPlugin {
 
 	private static final int MAX_ADDRESSES = 5;
 	private static final String PROP_IP_PORTS = "ipPorts";
-	private static final String PROP_IP_PORT = "ipPort";
 	private static final String SEPARATOR = ",";
 
 	LanTcpPlugin(Executor ioExecutor, Backoff backoff,
@@ -186,23 +191,26 @@ class LanTcpPlugin extends TcpPlugin {
 			LOG.info("Could not bind server socket for key agreement");
 			return null;
 		}
-		TransportProperties p = new TransportProperties();
+		BdfList descriptor = new BdfList();
-		SocketAddress local = ss.getLocalSocketAddress();
+		descriptor.add(TRANSPORT_ID_LAN);
-		p.put(PROP_IP_PORT, getIpPortString((InetSocketAddress) local));
+		InetSocketAddress local =
-		TransportDescriptor d = new TransportDescriptor(ID, p);
+				(InetSocketAddress) ss.getLocalSocketAddress();
-		return new LanKeyAgreementListener(d, ss);
+		descriptor.add(local.getAddress().getAddress());
+		descriptor.add(local.getPort());
+		return new LanKeyAgreementListener(descriptor, ss);
 	}
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		if (!isRunning()) return null;
-		if (!ID.equals(d.getIdentifier())) return null;
+		InetSocketAddress remote;
-		TransportProperties p = d.getProperties();
+		try {
-		if (p == null) return null;
+			remote = parseSocketAddress(descriptor);
-		String ipPort = p.get(PROP_IP_PORT);
+		} catch (FormatException e) {
-		InetSocketAddress remote = parseSocketAddress(ipPort);
+			LOG.info("Invalid IP/port in key agreement descriptor");
-		if (remote == null) return null;
+			return null;
+		}
 		if (!isConnectable(remote)) {
 			if (LOG.isLoggable(INFO)) {
 				SocketAddress local = socket.getLocalSocketAddress();
@@ -228,11 +236,25 @@ class LanTcpPlugin extends TcpPlugin {
 		}
 	}
 
+	private InetSocketAddress parseSocketAddress(BdfList descriptor)
+			throws FormatException {
+		byte[] address = descriptor.getRaw(1);
+		int port = descriptor.getLong(2).intValue();
+		if (port < 1 || port > MAX_16_BIT_UNSIGNED) throw new FormatException();
+		try {
+			InetAddress addr = InetAddress.getByAddress(address);
+			return new InetSocketAddress(addr, port);
+		} catch (UnknownHostException e) {
+			// Invalid address length
+			throw new FormatException();
+		}
+	}
+
 	private class LanKeyAgreementListener extends KeyAgreementListener {
 
 		private final ServerSocket ss;
 
-		public LanKeyAgreementListener(TransportDescriptor descriptor,
+		private LanKeyAgreementListener(BdfList descriptor,
 				ServerSocket ss) {
 			super(descriptor);
 			this.ss = ss;

briar-core/src/org/briarproject/plugins/tcp/TcpPlugin.java

@@ -2,8 +2,10 @@ package org.briarproject.plugins.tcp;
 
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
@@ -28,10 +30,14 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 import java.util.regex.Pattern;
 
+import javax.annotation.Nullable;
+
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.util.PrivacyUtils.scrubSocketAddress;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 abstract class TcpPlugin implements DuplexPlugin {
 
 	private static final Pattern DOTTED_QUAD =
@@ -141,7 +147,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 		});
 	}
 
-	protected void tryToClose(ServerSocket ss) {
+	protected void tryToClose(@Nullable ServerSocket ss) {
 		try {
 			if (ss != null) ss.close();
 		} catch (IOException e) {
@@ -252,6 +258,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 		return null;
 	}
 
+	@Nullable
 	protected InetSocketAddress parseSocketAddress(String ipPort) {
 		if (StringUtils.isNullOrEmpty(ipPort)) return null;
 		String[] split = ipPort.split(":");
@@ -298,7 +305,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		throw new UnsupportedOperationException();
 	}
 

briar-core/src/org/briarproject/plugins/tcp/WanTcpPlugin.java

@@ -2,6 +2,8 @@ package org.briarproject.plugins.tcp;
 
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
 import org.briarproject.api.properties.TransportProperties;
@@ -14,6 +16,8 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.Executor;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 class WanTcpPlugin extends TcpPlugin {
 
 	static final TransportId ID = new TransportId("wan");

briar-core/src/org/briarproject/util/StringUtils.java

@@ -1,24 +1,34 @@
 package org.briarproject.util;
 
+import org.briarproject.api.nullsafety.NotNullByDefault;
+
 import java.io.UnsupportedEncodingException;
 import java.nio.ByteBuffer;
 import java.nio.charset.CharacterCodingException;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.util.Collection;
+import java.util.regex.Pattern;
+
+import javax.annotation.Nullable;
 
 import static java.nio.charset.CodingErrorAction.IGNORE;
+import static java.util.regex.Pattern.CASE_INSENSITIVE;
 
+@NotNullByDefault
 public class StringUtils {
 
 	private static final Charset UTF_8 = Charset.forName("UTF-8");
+	private static Pattern MAC = Pattern.compile("[0-9a-f]{2}:[0-9a-f]{2}:" +
+					"[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}",
+			CASE_INSENSITIVE);
 
 	private static final char[] HEX = new char[] {
-		'0', '1', '2', '3', '4', '5', '6', '7',
+			'0', '1', '2', '3', '4', '5', '6', '7',
-		'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
+			'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
 	};
 
-	public static boolean isNullOrEmpty(String s) {
+	public static boolean isNullOrEmpty(@Nullable String s) {
 		return s == null || s.length() == 0;
 	}
 
@@ -61,7 +71,9 @@ public class StringUtils {
 		return fromUtf8(utf8, 0, maxUtf8Length);
 	}
 
-	/** Converts the given byte array to a hex character array. */
+	/**
+	 * Converts the given byte array to a hex character array.
+	 */
 	private static char[] toHexChars(byte[] bytes) {
 		char[] hex = new char[bytes.length * 2];
 		for (int i = 0, j = 0; i < bytes.length; i++) {
@@ -71,12 +83,16 @@ public class StringUtils {
 		return hex;
 	}
 
-	/** Converts the given byte array to a hex string. */
+	/**
+	 * Converts the given byte array to a hex string.
+	 */
 	public static String toHexString(byte[] bytes) {
 		return new String(toHexChars(bytes));
 	}
 
-	/** Converts the given hex string to a byte array. */
+	/**
+	 * Converts the given hex string to a byte array.
+	 */
 	public static byte[] fromHexString(String hex) {
 		int len = hex.length();
 		if (len % 2 != 0)
@@ -107,4 +123,20 @@ public class StringUtils {
 	public static boolean utf8IsTooLong(String s, int maxLength) {
 		return toUtf8(s).length > maxLength;
 	}
+
+	public static byte[] macToBytes(String mac) {
+		if (!MAC.matcher(mac).matches()) throw new IllegalArgumentException();
+		return fromHexString(mac.replaceAll(":", ""));
+	}
+
+	public static String macToString(byte[] mac) {
+		if (mac.length != 6) throw new IllegalArgumentException();
+		StringBuilder s = new StringBuilder();
+		for (byte b : mac) {
+			if (s.length() > 0) s.append(':');
+			s.append(HEX[(b >> 4) & 0xF]);
+			s.append(HEX[b & 0xF]);
+		}
+		return s.toString();
+	}
 }

briar-desktop/src/org/briarproject/plugins/bluetooth/BluetoothPlugin.java

@@ -1,11 +1,14 @@
 package org.briarproject.plugins.bluetooth;
 
+import org.briarproject.api.FormatException;
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
@@ -33,6 +36,7 @@ import java.util.concurrent.Semaphore;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
 import javax.bluetooth.BluetoothStateException;
 import javax.bluetooth.DiscoveryAgent;
 import javax.bluetooth.LocalDevice;
@@ -44,7 +48,10 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static javax.bluetooth.DiscoveryAgent.GIAC;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_BLUETOOTH;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 class BluetoothPlugin implements DuplexPlugin {
 
 	// Share an ID with the Android Bluetooth plugin
@@ -161,7 +168,7 @@ class BluetoothPlugin implements DuplexPlugin {
 		return uuid;
 	}
 
-	private void tryToClose(StreamConnectionNotifier ss) {
+	private void tryToClose(@Nullable StreamConnectionNotifier ss) {
 		try {
 			if (ss != null) ss.close();
 		} catch (IOException e) {
@@ -330,7 +337,7 @@ class BluetoothPlugin implements DuplexPlugin {
 	}
 
 	private void closeSockets(final List<Future<StreamConnection>> futures,
-			final StreamConnection chosen) {
+			@Nullable final StreamConnection chosen) {
 		ioExecutor.execute(new Runnable() {
 			@Override
 			public void run() {
@@ -382,21 +389,24 @@ class BluetoothPlugin implements DuplexPlugin {
 			tryToClose(ss);
 			return null;
 		}
-		TransportProperties p = new TransportProperties();
+		BdfList descriptor = new BdfList();
-		p.put(PROP_ADDRESS, localDevice.getBluetoothAddress());
+		descriptor.add(TRANSPORT_ID_BLUETOOTH);
-		TransportDescriptor d = new TransportDescriptor(ID, p);
+		String address = localDevice.getBluetoothAddress();
-		return new BluetoothKeyAgreementListener(d, ss);
+		descriptor.add(StringUtils.macToBytes(address));
+		return new BluetoothKeyAgreementListener(descriptor, ss);
 	}
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		if (!isRunning()) return null;
-		if (!ID.equals(d.getIdentifier())) return null;
+		String address;
-		TransportProperties p = d.getProperties();
+		try {
-		if (p == null) return null;
+			address = parseAddress(descriptor);
-		String address = p.get(PROP_ADDRESS);
+		} catch (FormatException e) {
-		if (StringUtils.isNullOrEmpty(address)) return null;
+			LOG.info("Invalid address in key agreement descriptor");
+			return null;
+		}
 		// No truncation necessary because COMMIT_LENGTH = 16
 		String uuid = UUID.nameUUIDFromBytes(commitment).toString();
 		if (LOG.isLoggable(INFO))
@@ -407,6 +417,12 @@ class BluetoothPlugin implements DuplexPlugin {
 		return new BluetoothTransportConnection(this, s);
 	}
 
+	private String parseAddress(BdfList descriptor) throws FormatException {
+		byte[] mac = descriptor.getRaw(1);
+		if (mac.length != 6) throw new FormatException();
+		return StringUtils.macToString(mac);
+	}
+
 	private void makeDeviceDiscoverable() {
 		// Try to make the device discoverable (requires root on Linux)
 		try {
@@ -491,7 +507,7 @@ class BluetoothPlugin implements DuplexPlugin {
 
 		private final StreamConnectionNotifier ss;
 
-		BluetoothKeyAgreementListener(TransportDescriptor descriptor,
+		BluetoothKeyAgreementListener(BdfList descriptor,
 				StreamConnectionNotifier ss) {
 			super(descriptor);
 			this.ss = ss;

briar-desktop/src/org/briarproject/plugins/file/RemovableDrivePlugin.java

@@ -2,6 +2,7 @@ package org.briarproject.plugins.file;
 
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.nullsafety.NotNullByDefault;
 import org.briarproject.api.plugins.simplex.SimplexPluginCallback;
 
 import java.io.File;
@@ -15,6 +16,7 @@ import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
 
+@NotNullByDefault
 class RemovableDrivePlugin extends FilePlugin
 implements RemovableDriveMonitor.Callback {
 

briar-desktop/src/org/briarproject/plugins/modem/ModemPlugin.java

@@ -3,8 +3,10 @@ package org.briarproject.plugins.modem;
 import org.briarproject.api.TransportId;
 import org.briarproject.api.contact.ContactId;
 import org.briarproject.api.crypto.PseudoRandom;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
+import org.briarproject.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.api.plugins.duplex.AbstractDuplexTransportConnection;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
@@ -22,6 +24,8 @@ import java.util.logging.Logger;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 class ModemPlugin implements DuplexPlugin, Modem.Callback {
 
 	static final TransportId ID = new TransportId("modem");
@@ -114,7 +118,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 		throw new UnsupportedOperationException();
 	}
 
-	boolean resetModem() {
+	private boolean resetModem() {
 		if (!running) return false;
 		for (String portName : serialPortList.getPortNames()) {
 			if (LOG.isLoggable(INFO))
@@ -184,7 +188,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, TransportDescriptor d, long timeout) {
+			byte[] commitment, BdfList descriptor, long timeout) {
 		throw new UnsupportedOperationException();
 	}
 

briar-tests/src/org/briarproject/plugins/tcp/LanTcpPluginTest.java

@@ -2,9 +2,9 @@ package org.briarproject.plugins.tcp;
 
 import org.briarproject.BriarTestCase;
 import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.data.BdfList;
 import org.briarproject.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.api.keyagreement.KeyAgreementListener;
-import org.briarproject.api.keyagreement.TransportDescriptor;
 import org.briarproject.api.plugins.Backoff;
 import org.briarproject.api.plugins.duplex.DuplexPlugin;
 import org.briarproject.api.plugins.duplex.DuplexPluginCallback;
@@ -27,11 +27,12 @@ import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import static java.util.concurrent.TimeUnit.SECONDS;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
+import static org.briarproject.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -188,23 +189,22 @@ public class LanTcpPluginTest extends BriarTestCase {
 				0, 0);
 		plugin.start();
 		assertTrue(callback.propertiesLatch.await(5, SECONDS));
-		KeyAgreementListener kal = plugin.createKeyAgreementListener(null);
+		KeyAgreementListener kal =
+				plugin.createKeyAgreementListener(new byte[COMMIT_LENGTH]);
+		assertNotNull(kal);
 		Callable<KeyAgreementConnection> c = kal.listen();
 		FutureTask<KeyAgreementConnection> f = new FutureTask<>(c);
 		new Thread(f).start();
 		// The plugin should have bound a socket and stored the port number
-		TransportDescriptor d = kal.getDescriptor();
+		BdfList descriptor = kal.getDescriptor();
-		TransportProperties p = d.getProperties();
+		assertEquals(3, descriptor.size());
-		String ipPort = p.get("ipPort");
+		assertEquals(TRANSPORT_ID_LAN, descriptor.getLong(0).longValue());
-		assertNotNull(ipPort);
+		byte[] address = descriptor.getRaw(1);
-		String[] split = ipPort.split(":");
+		InetAddress addr = InetAddress.getByAddress(address);
-		assertEquals(2, split.length);
-		String addrString = split[0], portString = split[1];
-		InetAddress addr = InetAddress.getByName(addrString);
 		assertTrue(addr instanceof Inet4Address);
 		assertFalse(addr.isLoopbackAddress());
 		assertTrue(addr.isLinkLocalAddress() || addr.isSiteLocalAddress());
-		int port = Integer.parseInt(portString);
+		int port = descriptor.getLong(2).intValue();
 		assertTrue(port > 0 && port < 65536);
 		// The plugin should be listening on the port
 		InetSocketAddress socketAddr = new InetSocketAddress(addr, port);
@@ -240,7 +240,6 @@ public class LanTcpPluginTest extends BriarTestCase {
 		// Listen on the same interface as the plugin
 		final ServerSocket ss = new ServerSocket();
 		ss.bind(new InetSocketAddress(addrString, 0), 10);
-		int port = ss.getLocalPort();
 		final CountDownLatch latch = new CountDownLatch(1);
 		final AtomicBoolean error = new AtomicBoolean(false);
 		new Thread() {
@@ -255,12 +254,15 @@ public class LanTcpPluginTest extends BriarTestCase {
 			}
 		}.start();
 		// Tell the plugin about the port
-		TransportProperties p = new TransportProperties();
+		BdfList descriptor = new BdfList();
-		p.put("ipPort", addrString + ":" + port);
+		descriptor.add(TRANSPORT_ID_LAN);
-		TransportDescriptor desc = new TransportDescriptor(plugin.getId(), p);
+		InetSocketAddress local =
+				(InetSocketAddress) ss.getLocalSocketAddress();
+		descriptor.add(local.getAddress().getAddress());
+		descriptor.add(local.getPort());
 		// Connect to the port
-		DuplexTransportConnection d =
+		DuplexTransportConnection d = plugin.createKeyAgreementConnection(
-				plugin.createKeyAgreementConnection(null, desc, 5000);
+				new byte[COMMIT_LENGTH], descriptor, 5000);
 		assertNotNull(d);
 		// Check that the connection was accepted
 		assertTrue(latch.await(5, SECONDS));
@@ -291,61 +293,76 @@ public class LanTcpPluginTest extends BriarTestCase {
 		private final CountDownLatch connectionsLatch = new CountDownLatch(1);
 		private final TransportProperties local = new TransportProperties();
 
+		@Override
 		public Settings getSettings() {
 			return new Settings();
 		}
 
+		@Override
 		public TransportProperties getLocalProperties() {
 			return local;
 		}
 
+		@Override
 		public Map<ContactId, TransportProperties> getRemoteProperties() {
 			return remote;
 		}
 
+		@Override
 		public void mergeSettings(Settings s) {
 		}
 
+		@Override
 		public void mergeLocalProperties(TransportProperties p) {
 			local.putAll(p);
 			propertiesLatch.countDown();
 		}
 
+		@Override
 		public int showChoice(String[] options, String... message) {
 			return -1;
 		}
 
+		@Override
 		public boolean showConfirmationMessage(String... message) {
 			return false;
 		}
 
+		@Override
 		public void showMessage(String... message) {
 		}
 
+		@Override
 		public void incomingConnectionCreated(DuplexTransportConnection d) {
 			connectionsLatch.countDown();
 		}
 
+		@Override
 		public void outgoingConnectionCreated(ContactId c,
 				DuplexTransportConnection d) {
 		}
 
+		@Override
 		public void transportEnabled() {
 		}
 
+		@Override
 		public void transportDisabled() {
 		}
 	}
 
 	private static class TestBackoff implements Backoff {
 
+		@Override
 		public int getPollingInterval() {
 			return 60 * 1000;
 		}
 
+		@Override
 		public void increment() {
 		}
 
+		@Override
 		public void reset() {
 		}
 	}

briar-tests/src/org/briarproject/util/StringUtilsTest.java

@@ -173,4 +173,55 @@ public class StringUtilsTest extends BriarTestCase {
 	public void testTruncateUtf8EmptyInput() {
 		assertEquals("", StringUtils.truncateUtf8("", 123));
 	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToBytesRejectsShortMac() {
+		StringUtils.macToBytes("00:00:00:00:00");
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToBytesRejectsLongMac() {
+		StringUtils.macToBytes("00:00:00:00:00:00:00");
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToBytesRejectsInvalidCharacter() {
+		StringUtils.macToBytes("00:00:00:00:00:0g");
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToBytesRejectsInvalidFormat() {
+		StringUtils.macToBytes("0:000:00:00:00:00");
+	}
+
+	@Test
+	public void testMacToBytesUpperCase() {
+		byte[] expected = new byte[] {0x0A, 0x1B, 0x2C, 0x3D, 0x4E, 0x5F};
+		String mac = "0A:1B:2C:3D:4E:5F";
+		assertArrayEquals(expected, StringUtils.macToBytes(mac));
+	}
+
+	@Test
+	public void testMacToBytesLowerCase() {
+		byte[] expected = new byte[] {0x0A, 0x1B, 0x2C, 0x3D, 0x4E, 0x5F};
+		String mac = "0a:1b:2c:3d:4e:5f";
+		assertArrayEquals(expected, StringUtils.macToBytes(mac));
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToStringRejectsShortMac() {
+		StringUtils.macToString(new byte[5]);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testMacToStringRejectsLongMac() {
+		StringUtils.macToString(new byte[7]);
+	}
+
+	@Test
+	public void testMacToString() {
+		byte[] mac = new byte[] {0x0a, 0x1b, 0x2c, 0x3d, 0x4e, 0x5f};
+		String expected = "0A:1B:2C:3D:4E:5F";
+		assertEquals(expected, StringUtils.macToString(mac));
+	}
 }