Try all transports in order of preference.

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/duplex/DuplexPlugin.java

@@ -41,12 +41,10 @@ public interface DuplexPlugin extends Plugin {
 	/**
 	 * Attempts to connect to the remote peer specified in the given descriptor.
 	 * Returns null if no connection can be established.
-	 *
-	 * @param alice True if the local party is Alice
 	 */
 	@Nullable
 	DuplexTransportConnection createKeyAgreementConnection(
-			byte[] remoteCommitment, BdfList descriptor, boolean alice);
+			byte[] remoteCommitment, BdfList descriptor);
 
 	/**
 	 * Returns true if the plugin supports rendezvous connections.

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.keyagreement;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.crypto.KeyAgreementCrypto;
 import org.briarproject.bramble.api.crypto.KeyPair;
 import org.briarproject.bramble.api.data.BdfList;
@@ -114,7 +115,7 @@ class KeyAgreementConnector {
 		this.alice = alice;
 		aliceLatch.countDown();
 
-		// Start connecting over best available transport
+		// Start connecting over supported transports in order of preference
 		if (LOG.isLoggable(INFO)) {
 			LOG.info("Starting outgoing BQP connections as "
 					+ (alice ? "Alice" : "Bob"));
@@ -123,24 +124,26 @@ class KeyAgreementConnector {
 		for (TransportDescriptor d : remotePayload.getTransportDescriptors()) {
 			descriptors.put(d.getId(), d);
 		}
+		List<Pair<DuplexPlugin, BdfList>> transports = new ArrayList<>();
 		for (TransportId id : PREFERRED_TRANSPORTS) {
 			TransportDescriptor d = descriptors.get(id);
 			Plugin p = pluginManager.getPlugin(id);
 			if (d != null && p instanceof DuplexPlugin) {
 				if (LOG.isLoggable(INFO))
 					LOG.info("Connecting via " + id);
-				DuplexPlugin plugin = (DuplexPlugin) p;
-				byte[] commitment = remotePayload.getCommitment();
-				BdfList descriptor = d.getDescriptor();
-				connectionChooser.submit(new ReadableTask(new ConnectorTask(
-						plugin, commitment, descriptor, alice)));
-				break;
+				transports.add(new Pair<>((DuplexPlugin) p, d.getDescriptor()));
 			}
 		}
 
 		// TODO: If we don't have any transports in common with the peer,
 		//  warn the user and give up (#1224)
 
+		if (!transports.isEmpty()) {
+			byte[] commitment = remotePayload.getCommitment();
+			connectionChooser.submit(new ReadableTask(new ConnectorTask(
+					transports, commitment)));
+		}
+
 		// Get chosen connection
 		try {
 			KeyAgreementConnection chosen =
@@ -166,17 +169,13 @@ class KeyAgreementConnector {
 
 	private class ConnectorTask implements Callable<KeyAgreementConnection> {
 
-		private final DuplexPlugin plugin;
+		private final List<Pair<DuplexPlugin, BdfList>> transports;
 		private final byte[] commitment;
-		private final BdfList descriptor;
-		private final boolean alice;
 
-		private ConnectorTask(DuplexPlugin plugin, byte[] commitment,
-				BdfList descriptor, boolean alice) {
-			this.plugin = plugin;
+		private ConnectorTask(List<Pair<DuplexPlugin, BdfList>> transports,
+				byte[] commitment) {
+			this.transports = transports;
 			this.commitment = commitment;
-			this.descriptor = descriptor;
-			this.alice = alice;
 		}
 
 		@Nullable
@@ -184,13 +183,18 @@ class KeyAgreementConnector {
 		public KeyAgreementConnection call() throws Exception {
 			// Repeat attempts until we connect, get stopped, or get interrupted
 			while (!stopped) {
-				DuplexTransportConnection conn =
-						plugin.createKeyAgreementConnection(commitment,
-								descriptor, alice);
-				if (conn != null) {
-					if (LOG.isLoggable(INFO))
-						LOG.info(plugin.getId() + ": Outgoing connection");
-					return new KeyAgreementConnection(conn, plugin.getId());
+				for (Pair<DuplexPlugin, BdfList> pair : transports) {
+					if (stopped) return null;
+					DuplexPlugin plugin = pair.getFirst();
+					BdfList descriptor = pair.getSecond();
+					DuplexTransportConnection conn =
+							plugin.createKeyAgreementConnection(commitment,
+									descriptor);
+					if (conn != null) {
+						if (LOG.isLoggable(INFO))
+							LOG.info(plugin.getId() + ": Outgoing connection");
+						return new KeyAgreementConnection(conn, plugin.getId());
+					}
 				}
 				// Wait 2s before retry (to circumvent transient failures)
 				Thread.sleep(2000);

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

@@ -430,22 +430,17 @@ abstract class BluetoothPlugin<S, SS> implements DuplexPlugin, EventListener {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, BdfList descriptor, boolean alice) {
+			byte[] commitment, BdfList descriptor) {
 		if (getState() != ACTIVE) return null;
 		// No truncation necessary because COMMIT_LENGTH = 16
 		String uuid = UUID.nameUUIDFromBytes(commitment).toString();
 		DuplexTransportConnection conn;
 		if (descriptor.size() == 1) {
-			if (alice) {
-				if (LOG.isLoggable(INFO)) {
-					LOG.info("Discovering address for key agreement UUID " +
-							uuid);
-				}
-				conn = discoverAndConnect(uuid);
-			} else {
-				LOG.info("No address in key agreement descriptor");
-				return null;
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Discovering address for key agreement UUID " +
+						uuid);
 			}
+			conn = discoverAndConnect(uuid);
 		} else {
 			String address;
 			try {

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

@@ -376,7 +376,7 @@ class LanTcpPlugin extends TcpPlugin {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, BdfList descriptor, boolean alice) {
+			byte[] commitment, BdfList descriptor) {
 		ServerSocket ss = state.getServerSocket(true);
 		if (ss == null) return null;
 		InterfaceAddress local = getLocalInterfaceAddress(ss.getInetAddress());

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

@@ -367,7 +367,7 @@ abstract class TcpPlugin implements DuplexPlugin, EventListener {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, BdfList descriptor, boolean alice) {
+			byte[] commitment, BdfList descriptor) {
 		throw new UnsupportedOperationException();
 	}
 

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

@@ -708,7 +708,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, BdfList descriptor, boolean alice) {
+			byte[] commitment, BdfList descriptor) {
 		throw new UnsupportedOperationException();
 	}
 

bramble-core/src/test/java/org/briarproject/bramble/plugin/tcp/LanTcpPluginTest.java

@@ -276,7 +276,7 @@ public class LanTcpPluginTest extends BrambleTestCase {
 		descriptor.add(local.getPort());
 		// Connect to the port
 		DuplexTransportConnection d = plugin.createKeyAgreementConnection(
-				new byte[COMMIT_LENGTH], descriptor, true);
+				new byte[COMMIT_LENGTH], descriptor);
 		assertNotNull(d);
 		// Check that the connection was accepted
 		assertTrue(latch.await(5, SECONDS));

bramble-java/src/main/java/org/briarproject/bramble/plugin/modem/ModemPlugin.java

@@ -198,7 +198,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
-			byte[] commitment, BdfList descriptor, boolean alice) {
+			byte[] commitment, BdfList descriptor) {
 		throw new UnsupportedOperationException();
 	}