Remove unused parameter.

This should reduce the impact of connections that fail at the remote
end.

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

@@ -67,7 +67,7 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl();
+				new BluetoothConnectionLimiterImpl(eventBus, clock);
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidBluetoothPlugin plugin = new AndroidBluetoothPlugin(

bramble-api/src/main/java/org/briarproject/bramble/api/connection/ConnectionManager.java

@@ -1,8 +1,11 @@
-package org.briarproject.bramble.api.plugin;
+package org.briarproject.bramble.api.connection;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 
 @NotNullByDefault

bramble-api/src/main/java/org/briarproject/bramble/api/connection/ConnectionRegistry.java

@@ -0,0 +1,130 @@
+package org.briarproject.bramble.api.connection;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+
+import java.util.Collection;
+
+/**
+ * Keeps track of which contacts are currently connected by which transports.
+ */
+@NotNullByDefault
+public interface ConnectionRegistry {
+
+	/**
+	 * Registers an incoming connection from the given contact over the given
+	 * transport. The connection's {@link Priority priority} can be set later
+	 * via {@link #setPriority(ContactId, TransportId, InterruptibleConnection,
+	 * Priority)} if a priority record is received from the contact.
+	 * <p>
+	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
+	 * {@link ContactConnectedEvent} if this is the only connection with the
+	 * contact.
+	 */
+	void registerIncomingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn);
+
+	/**
+	 * Registers an outgoing connection to the given contact over the given
+	 * transport.
+	 * <p>
+	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
+	 * {@link ContactConnectedEvent} if this is the only connection with the
+	 * contact.
+	 * <p>
+	 * If the registry has any "better" connections with the given contact, the
+	 * given connection will be interrupted. If the registry has any "worse"
+	 * connections with the given contact, those connections will be
+	 * interrupted.
+	 * <p>
+	 * Connection A is considered "better" than connection B if both
+	 * connections have had their priorities set, and either A's transport is
+	 * {@link PluginConfig#getTransportPreferences() preferred} to B's, or
+	 * they use the same transport and A has higher {@link Priority priority}
+	 * than B.
+	 * <p>
+	 * For backward compatibility, connections without priorities are not
+	 * considered better or worse than other connections.
+	 */
+	void registerOutgoingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority);
+
+	/**
+	 * Unregisters a connection with the given contact over the given transport.
+	 * <p>
+	 * Broadcasts {@link ConnectionClosedEvent}. Also broadcasts
+	 * {@link ContactDisconnectedEvent} if this is the only connection with
+	 * the contact.
+	 */
+	void unregisterConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, boolean incoming, boolean exception);
+
+	/**
+	 * Sets the {@link Priority priority} of a connection that was previously
+	 * registered via {@link #registerIncomingConnection(ContactId, TransportId,
+	 * InterruptibleConnection)}.
+	 * <p>
+	 * If the registry has any "better" connections with the given contact, the
+	 * given connection will be interrupted. If the registry has any "worse"
+	 * connections with the given contact, those connections will be
+	 * interrupted.
+	 * <p>
+	 * Connection A is considered "better" than connection B if both
+	 * connections have had their priorities set, and either A's transport is
+	 * {@link PluginConfig#getTransportPreferences() preferred} to B's, or
+	 * they use the same transport and A has higher {@link Priority priority}
+	 * than B.
+	 * <p>
+	 * For backward compatibility, connections without priorities are not
+	 * considered better or worse than other connections.
+	 */
+	void setPriority(ContactId c, TransportId t, InterruptibleConnection conn,
+			Priority priority);
+
+	/**
+	 * Returns any contacts that are connected via the given transport.
+	 */
+	Collection<ContactId> getConnectedContacts(TransportId t);
+
+	/**
+	 * Returns any contacts that are connected via the given transport or any
+	 * {@link PluginConfig#getTransportPreferences() better} transport.
+	 */
+	Collection<ContactId> getConnectedOrBetterContacts(TransportId t);
+
+	/**
+	 * Returns true if the given contact is connected via the given transport.
+	 */
+	boolean isConnected(ContactId c, TransportId t);
+
+	/**
+	 * Returns true if the given contact is connected via any transport.
+	 */
+	boolean isConnected(ContactId c);
+
+	/**
+	 * Registers a connection with the given pending contact. Broadcasts
+	 * {@link RendezvousConnectionOpenedEvent} if this is the only connection
+	 * with the pending contact.
+	 *
+	 * @return True if this is the only connection with the pending contact,
+	 * false if it is redundant and should be closed
+	 */
+	boolean registerConnection(PendingContactId p);
+
+	/**
+	 * Unregisters a connection with the given pending contact. Broadcasts
+	 * {@link RendezvousConnectionClosedEvent}.
+	 */
+	void unregisterConnection(PendingContactId p, boolean success);
+}

bramble-api/src/main/java/org/briarproject/bramble/api/connection/InterruptibleConnection.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.connection;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+/**
+ * A duplex sync connection that can be closed by interrupting its outgoing
+ * sync session.
+ */
+@NotNullByDefault
+public interface InterruptibleConnection {
+
+	/**
+	 * Interrupts the connection's outgoing sync session. If the underlying
+	 * transport connection is alive and the remote peer is cooperative, this
+	 * should result in both sync sessions ending and the connection being
+	 * cleanly closed.
+	 */
+	void interruptOutgoingSession();
+}

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

@@ -1,67 +0,0 @@
-package org.briarproject.bramble.api.plugin;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-
-import java.util.Collection;
-
-/**
- * Keeps track of which contacts are currently connected by which transports.
- */
-@NotNullByDefault
-public interface ConnectionRegistry {
-
-	/**
-	 * Registers a connection with the given contact over the given transport.
-	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
-	 * {@link ContactConnectedEvent} if this is the only connection with the
-	 * contact.
-	 */
-	void registerConnection(ContactId c, TransportId t, boolean incoming);
-
-	/**
-	 * Unregisters a connection with the given contact over the given transport.
-	 * Broadcasts {@link ConnectionClosedEvent}. Also broadcasts
-	 * {@link ContactDisconnectedEvent} if this is the only connection with
-	 * the contact.
-	 */
-	void unregisterConnection(ContactId c, TransportId t, boolean incoming);
-
-	/**
-	 * Returns any contacts that are connected via the given transport.
-	 */
-	Collection<ContactId> getConnectedContacts(TransportId t);
-
-	/**
-	 * Returns true if the given contact is connected via the given transport.
-	 */
-	boolean isConnected(ContactId c, TransportId t);
-
-	/**
-	 * Returns true if the given contact is connected via any transport.
-	 */
-	boolean isConnected(ContactId c);
-
-	/**
-	 * Registers a connection with the given pending contact. Broadcasts
-	 * {@link RendezvousConnectionOpenedEvent} if this is the only connection
-	 * with the pending contact.
-	 *
-	 * @return True if this is the only connection with the pending contact,
-	 * false if it is redundant and should be closed
-	 */
-	boolean registerConnection(PendingContactId p);
-
-	/**
-	 * Unregisters a connection with the given pending contact. Broadcasts
-	 * {@link RendezvousConnectionClosedEvent}.
-	 */
-	void unregisterConnection(PendingContactId p, boolean success);
-}

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

@@ -5,6 +5,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 
 @NotNullByDefault
 public interface PluginConfig {
@@ -14,4 +16,11 @@ public interface PluginConfig {
 	Collection<SimplexPluginFactory> getSimplexFactories();
 
 	boolean shouldPoll();
+
+	/**
+	 * Returns a map representing transport preferences. For each entry in the
+	 * map, connections via the transports identified by the value are
+	 * preferred to connections via the transport identified by the key.
+	 */
+	Map<TransportId, List<TransportId>> getTransportPreferences();
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/ConnectionClosedEvent.java

@@ -13,13 +13,14 @@ public class ConnectionClosedEvent extends Event {
 
 	private final ContactId contactId;
 	private final TransportId transportId;
-	private final boolean incoming;
+	private final boolean incoming, exception;
 
 	public ConnectionClosedEvent(ContactId contactId, TransportId transportId,
-			boolean incoming) {
+			boolean incoming, boolean exception) {
 		this.contactId = contactId;
 		this.transportId = transportId;
 		this.incoming = incoming;
+		this.exception = exception;
 	}
 
 	public ContactId getContactId() {
@@ -33,4 +34,8 @@ public class ConnectionClosedEvent extends Event {
 	public boolean isIncoming() {
 		return incoming;
 	}
+
+	public boolean isException() {
+		return exception;
+	}
 }

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

@@ -0,0 +1,23 @@
+package org.briarproject.bramble.api.sync;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A record containing a nonce for choosing between redundant sessions.
+ */
+@Immutable
+@NotNullByDefault
+public class Priority {
+
+	private final byte[] nonce;
+
+	public Priority(byte[] nonce) {
+		this.nonce = nonce;
+	}
+
+	public byte[] getNonce() {
+		return nonce;
+	}
+}

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

@@ -0,0 +1,13 @@
+package org.briarproject.bramble.api.sync;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+/**
+ * An interface for handling a {@link Priority} record received by an
+ * incoming {@link SyncSession}.
+ */
+@NotNullByDefault
+public interface PriorityHandler {
+
+	void handle(Priority p);
+}

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

@@ -10,4 +10,5 @@ public interface RecordTypes {
 	byte OFFER = 2;
 	byte REQUEST = 3;
 	byte VERSIONS = 4;
+	byte PRIORITY = 5;
 }

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

@@ -49,4 +49,10 @@ public interface SyncConstants {
 	 * simultaneously.
 	 */
 	int MAX_SUPPORTED_VERSIONS = 10;
+
+	/**
+	 * The length of the priority nonce used for choosing between redundant
+	 * connections.
+	 */
+	int PRIORITY_NONCE_BYTES = 16;
 }

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

@@ -28,4 +28,8 @@ public interface SyncRecordReader {
 	boolean hasVersions() throws IOException;
 
 	Versions readVersions() throws IOException;
+
+	boolean hasPriority() throws IOException;
+
+	Priority readPriority() throws IOException;
 }

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

@@ -17,5 +17,7 @@ public interface SyncRecordWriter {
 
 	void writeVersions(Versions v) throws IOException;
 
+	void writePriority(Priority p) throws IOException;
+
 	void flush() throws IOException;
 }

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

@@ -2,18 +2,23 @@ package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.InputStream;
 
+import javax.annotation.Nullable;
+
 @NotNullByDefault
 public interface SyncSessionFactory {
 
-	SyncSession createIncomingSession(ContactId c, InputStream in);
+	SyncSession createIncomingSession(ContactId c, InputStream in,
+			PriorityHandler handler);
 
-	SyncSession createSimplexOutgoingSession(ContactId c, int maxLatency,
-			StreamWriter streamWriter);
+	SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, StreamWriter streamWriter);
 
-	SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter);
+	SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, int maxIdleTime, StreamWriter streamWriter,
+			@Nullable Priority priority);
 }

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

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.sync.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when all sync connections using a given
+ * transport should be closed.
+ */
+@Immutable
+@NotNullByDefault
+public class CloseSyncConnectionsEvent extends Event {
+
+	private final TransportId transportId;
+
+	public CloseSyncConnectionsEvent(TransportId transportId) {
+		this.transportId = transportId;
+	}
+
+	public TransportId getTransportId() {
+		return transportId;
+	}
+}

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

@@ -1,6 +1,7 @@
 package org.briarproject.bramble;
 
 import org.briarproject.bramble.client.ClientModule;
+import org.briarproject.bramble.connection.ConnectionModule;
 import org.briarproject.bramble.contact.ContactModule;
 import org.briarproject.bramble.crypto.CryptoExecutorModule;
 import org.briarproject.bramble.crypto.CryptoModule;
@@ -28,6 +29,7 @@ import dagger.Module;
 
 @Module(includes = {
 		ClientModule.class,
+		ConnectionModule.class,
 		ContactModule.class,
 		CryptoModule.class,
 		CryptoExecutorModule.class,

bramble-core/src/main/java/org/briarproject/bramble/connection/Connection.java

@@ -0,0 +1,79 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+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.api.transport.TransportConstants.TAG_LENGTH;
+import static org.briarproject.bramble.util.IoUtils.read;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+abstract class Connection {
+
+	protected static final Logger LOG = getLogger(Connection.class.getName());
+
+	final KeyManager keyManager;
+	final ConnectionRegistry connectionRegistry;
+	final StreamReaderFactory streamReaderFactory;
+	final StreamWriterFactory streamWriterFactory;
+
+	Connection(KeyManager keyManager, ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory) {
+		this.keyManager = keyManager;
+		this.connectionRegistry = connectionRegistry;
+		this.streamReaderFactory = streamReaderFactory;
+		this.streamWriterFactory = streamWriterFactory;
+	}
+
+	@Nullable
+	StreamContext recogniseTag(TransportConnectionReader reader,
+			TransportId transportId) {
+		StreamContext ctx;
+		try {
+			byte[] tag = readTag(reader.getInputStream());
+			return keyManager.getStreamContext(transportId, tag);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	private byte[] readTag(InputStream in) throws IOException {
+		byte[] tag = new byte[TAG_LENGTH];
+		read(in, tag);
+		return tag;
+	}
+
+	void disposeOnError(TransportConnectionReader reader, boolean recognised) {
+		try {
+			reader.dispose(true, recognised);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+
+	void disposeOnError(TransportConnectionWriter writer) {
+		try {
+			writer.dispose(true);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+}

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

@@ -0,0 +1,114 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.security.SecureRandom;
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+@Immutable
+@NotNullByDefault
+class ConnectionManagerImpl implements ConnectionManager {
+
+	private final Executor ioExecutor;
+	private final KeyManager keyManager;
+	private final StreamReaderFactory streamReaderFactory;
+	private final StreamWriterFactory streamWriterFactory;
+	private final SyncSessionFactory syncSessionFactory;
+	private final HandshakeManager handshakeManager;
+	private final ContactExchangeManager contactExchangeManager;
+	private final ConnectionRegistry connectionRegistry;
+	private final TransportPropertyManager transportPropertyManager;
+	private final SecureRandom secureRandom;
+
+	@Inject
+	ConnectionManagerImpl(@IoExecutor Executor ioExecutor,
+			KeyManager keyManager, StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionRegistry connectionRegistry,
+			TransportPropertyManager transportPropertyManager,
+			SecureRandom secureRandom) {
+		this.ioExecutor = ioExecutor;
+		this.keyManager = keyManager;
+		this.streamReaderFactory = streamReaderFactory;
+		this.streamWriterFactory = streamWriterFactory;
+		this.syncSessionFactory = syncSessionFactory;
+		this.handshakeManager = handshakeManager;
+		this.contactExchangeManager = contactExchangeManager;
+		this.connectionRegistry = connectionRegistry;
+		this.transportPropertyManager = transportPropertyManager;
+		this.secureRandom = secureRandom;
+	}
+
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			TransportConnectionReader r) {
+		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, t, r));
+	}
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new IncomingDuplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, ioExecutor,
+				t, d));
+	}
+
+	@Override
+	public void manageIncomingConnection(PendingContactId p, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new IncomingHandshakeConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				handshakeManager, contactExchangeManager, this, p, t, d));
+	}
+
+	@Override
+	public void manageOutgoingConnection(ContactId c, TransportId t,
+			TransportConnectionWriter w) {
+		ioExecutor.execute(new OutgoingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, c, t, w));
+	}
+
+	@Override
+	public void manageOutgoingConnection(ContactId c, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new OutgoingDuplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, ioExecutor,
+				secureRandom, c, t, d));
+	}
+
+	@Override
+	public void manageOutgoingConnection(PendingContactId p, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new OutgoingHandshakeConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				handshakeManager, contactExchangeManager, this, p, t, d));
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/ConnectionModule.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ConnectionModule {
+
+	@Provides
+	ConnectionManager provideConnectionManager(
+			ConnectionManagerImpl connectionManager) {
+		return connectionManager;
+	}
+
+	@Provides
+	@Singleton
+	ConnectionRegistry provideConnectionRegistry(
+			ConnectionRegistryImpl connectionRegistry) {
+		return connectionRegistry;
+	}
+}

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

@@ -0,0 +1,289 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.Bytes;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+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 =
+			getLogger(ConnectionRegistryImpl.class.getName());
+
+	private final EventBus eventBus;
+	private final Map<TransportId, List<TransportId>> transportPrefs;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final Map<ContactId, List<ConnectionRecord>> contactConnections;
+	@GuardedBy("lock")
+	private final Set<PendingContactId> connectedPendingContacts;
+
+	@Inject
+	ConnectionRegistryImpl(EventBus eventBus, PluginConfig pluginConfig) {
+		this.eventBus = eventBus;
+		transportPrefs = pluginConfig.getTransportPreferences();
+		contactConnections = new HashMap<>();
+		connectedPendingContacts = new HashSet<>();
+	}
+
+	@Override
+	public void registerIncomingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn) {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Incoming connection registered: " + t);
+		}
+		registerConnection(c, t, conn, true);
+	}
+
+	@Override
+	public void registerOutgoingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority) {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Outgoing connection registered: " + t);
+		}
+		registerConnection(c, t, conn, false);
+		setPriority(c, t, conn, priority);
+	}
+
+	private void registerConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, boolean incoming) {
+		if (LOG.isLoggable(INFO)) {
+			if (incoming) LOG.info("Incoming connection registered: " + t);
+			else LOG.info("Outgoing connection registered: " + t);
+		}
+		boolean firstConnection;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) {
+				recs = new ArrayList<>();
+				contactConnections.put(c, recs);
+			}
+			firstConnection = recs.isEmpty();
+			recs.add(new ConnectionRecord(t, conn));
+		}
+		eventBus.broadcast(new ConnectionOpenedEvent(c, t, incoming));
+		if (firstConnection) {
+			LOG.info("Contact connected");
+			eventBus.broadcast(new ContactConnectedEvent(c));
+		}
+	}
+
+	@Override
+	public void setPriority(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority) {
+		if (LOG.isLoggable(INFO)) LOG.info("Setting connection priority: " + t);
+		List<InterruptibleConnection> toInterrupt;
+		boolean interruptNewConnection = false;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) throw new IllegalArgumentException();
+			toInterrupt = new ArrayList<>(recs.size());
+			for (ConnectionRecord rec : recs) {
+				if (rec.conn == conn) {
+					// Store the priority of this connection
+					rec.priority = priority;
+				} else if (rec.priority != null) {
+					int compare = compareConnections(t, priority,
+							rec.transportId, rec.priority);
+					if (compare == -1) {
+						// The old connection is better than the new one
+						interruptNewConnection = true;
+					} else if (compare == 1 && !rec.interrupted) {
+						// The new connection is better than the old one
+						toInterrupt.add(rec.conn);
+						rec.interrupted = true;
+					}
+				}
+			}
+		}
+		if (interruptNewConnection) {
+			LOG.info("Interrupting new connection");
+			conn.interruptOutgoingSession();
+		}
+		for (InterruptibleConnection old : toInterrupt) {
+			LOG.info("Interrupting old connection");
+			old.interruptOutgoingSession();
+		}
+	}
+
+	private int compareConnections(TransportId tA, Priority pA, TransportId tB,
+			Priority pB) {
+		if (getBetterTransports(tA).contains(tB)) return -1;
+		if (getBetterTransports(tB).contains(tA)) return 1;
+		return tA.equals(tB) ? Bytes.compare(pA.getNonce(), pB.getNonce()) : 0;
+	}
+
+	private List<TransportId> getBetterTransports(TransportId t) {
+		List<TransportId> better = transportPrefs.get(t);
+		return better == null ? emptyList() : better;
+	}
+
+	@Override
+	public void unregisterConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, boolean incoming, boolean exception) {
+		if (LOG.isLoggable(INFO)) {
+			if (incoming) LOG.info("Incoming connection unregistered: " + t);
+			else LOG.info("Outgoing connection unregistered: " + t);
+		}
+		boolean lastConnection;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null || !recs.remove(new ConnectionRecord(t, conn)))
+				throw new IllegalArgumentException();
+			lastConnection = recs.isEmpty();
+		}
+		eventBus.broadcast(
+				new ConnectionClosedEvent(c, t, incoming, exception));
+		if (lastConnection) {
+			LOG.info("Contact disconnected");
+			eventBus.broadcast(new ContactDisconnectedEvent(c));
+		}
+	}
+
+	@Override
+	public Collection<ContactId> getConnectedContacts(TransportId t) {
+		synchronized (lock) {
+			List<ContactId> contactIds = new ArrayList<>();
+			for (Entry<ContactId, List<ConnectionRecord>> e :
+					contactConnections.entrySet()) {
+				for (ConnectionRecord rec : e.getValue()) {
+					if (rec.transportId.equals(t)) {
+						contactIds.add(e.getKey());
+						break;
+					}
+				}
+			}
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(contactIds.size() + " contacts connected: " + t);
+			}
+			return contactIds;
+		}
+	}
+
+	@Override
+	public Collection<ContactId> getConnectedOrBetterContacts(TransportId t) {
+		synchronized (lock) {
+			List<TransportId> better = getBetterTransports(t);
+			List<ContactId> contactIds = new ArrayList<>();
+			for (Entry<ContactId, List<ConnectionRecord>> e :
+					contactConnections.entrySet()) {
+				for (ConnectionRecord rec : e.getValue()) {
+					if (rec.transportId.equals(t) ||
+							better.contains(rec.transportId)) {
+						contactIds.add(e.getKey());
+						break;
+					}
+				}
+			}
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(contactIds.size()
+						+ " contacts connected or better: " + t);
+			}
+			return contactIds;
+		}
+	}
+
+	@Override
+	public boolean isConnected(ContactId c, TransportId t) {
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) return false;
+			for (ConnectionRecord rec : recs) {
+				if (rec.transportId.equals(t)) return true;
+			}
+			return false;
+		}
+	}
+
+	@Override
+	public boolean isConnected(ContactId c) {
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			return recs != null && !recs.isEmpty();
+		}
+	}
+
+	@Override
+	public boolean registerConnection(PendingContactId p) {
+		boolean added;
+		synchronized (lock) {
+			added = connectedPendingContacts.add(p);
+		}
+		if (added) eventBus.broadcast(new RendezvousConnectionOpenedEvent(p));
+		return added;
+	}
+
+	@Override
+	public void unregisterConnection(PendingContactId p, boolean success) {
+		synchronized (lock) {
+			if (!connectedPendingContacts.remove(p))
+				throw new IllegalArgumentException();
+		}
+		eventBus.broadcast(new RendezvousConnectionClosedEvent(p, success));
+	}
+
+	private static class ConnectionRecord {
+
+		private final TransportId transportId;
+		private final InterruptibleConnection conn;
+		@GuardedBy("lock")
+		@Nullable
+		private Priority priority = null;
+		@GuardedBy("lock")
+		private boolean interrupted = false;
+
+		private ConnectionRecord(TransportId transportId,
+				InterruptibleConnection conn) {
+			this.transportId = transportId;
+			this.conn = conn;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (o instanceof ConnectionRecord) {
+				return conn == ((ConnectionRecord) o).conn;
+			} else {
+				return false;
+			}
+		}
+
+		@Override
+		public int hashCode() {
+			return conn.hashCode();
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java

@@ -0,0 +1,109 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.util.concurrent.Executor;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+
+@NotNullByDefault
+abstract class DuplexSyncConnection extends SyncConnection
+		implements InterruptibleConnection {
+
+	final Executor ioExecutor;
+	final TransportId transportId;
+	final TransportConnectionReader reader;
+	final TransportConnectionWriter writer;
+	final TransportProperties remote;
+
+	private final Object interruptLock = new Object();
+
+	@GuardedBy("interruptLock")
+	@Nullable
+	private SyncSession outgoingSession = null;
+	@GuardedBy("interruptLock")
+	private boolean interruptWaiting = false;
+
+	@Override
+	public void interruptOutgoingSession() {
+		SyncSession out = null;
+		synchronized (interruptLock) {
+			if (outgoingSession == null) interruptWaiting = true;
+			else out = outgoingSession;
+		}
+		if (out != null) out.interrupt();
+	}
+
+	void setOutgoingSession(SyncSession outgoingSession) {
+		boolean interruptWasWaiting = false;
+		synchronized (interruptLock) {
+			this.outgoingSession = outgoingSession;
+			if (interruptWaiting) {
+				interruptWasWaiting = true;
+				interruptWaiting = false;
+			}
+		}
+		if (interruptWasWaiting) outgoingSession.interrupt();
+	}
+
+	DuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, TransportId transportId,
+			DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.ioExecutor = ioExecutor;
+		this.transportId = transportId;
+		reader = connection.getReader();
+		writer = connection.getWriter();
+		remote = connection.getRemoteProperties();
+	}
+
+	void onReadError(boolean recognised) {
+		disposeOnError(reader, recognised);
+		disposeOnError(writer);
+		interruptOutgoingSession();
+	}
+
+	void onWriteError() {
+		disposeOnError(reader, true);
+		disposeOnError(writer);
+	}
+
+	SyncSession createDuplexOutgoingSession(StreamContext ctx,
+			TransportConnectionWriter w, @Nullable Priority priority)
+			throws IOException {
+		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
+				w.getOutputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createDuplexOutgoingSession(c,
+				ctx.getTransportId(), w.getMaxLatency(), w.getMaxIdleTime(),
+				streamWriter, priority);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/HandshakeConnection.java

@@ -0,0 +1,72 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+abstract class HandshakeConnection extends Connection {
+
+	final HandshakeManager handshakeManager;
+	final ContactExchangeManager contactExchangeManager;
+	final ConnectionManager connectionManager;
+	final PendingContactId pendingContactId;
+	final TransportId transportId;
+	final DuplexTransportConnection connection;
+	final TransportConnectionReader reader;
+	final TransportConnectionWriter writer;
+
+	HandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory);
+		this.handshakeManager = handshakeManager;
+		this.contactExchangeManager = contactExchangeManager;
+		this.connectionManager = connectionManager;
+		this.pendingContactId = pendingContactId;
+		this.transportId = transportId;
+		this.connection = connection;
+		reader = connection.getReader();
+		writer = connection.getWriter();
+	}
+
+	@Nullable
+	StreamContext allocateStreamContext(PendingContactId pendingContactId,
+			TransportId transportId) {
+		try {
+			return keyManager.getStreamContext(pendingContactId, transportId);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	void onError(boolean recognised) {
+		disposeOnError(reader, recognised);
+		disposeOnError(writer);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java

@@ -0,0 +1,107 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.util.concurrent.Executor;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingDuplexSyncConnection extends DuplexSyncConnection
+		implements Runnable {
+
+	IncomingDuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, TransportId transportId,
+			DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager, ioExecutor, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		if (ctx == null) {
+			LOG.info("Unrecognised tag");
+			onReadError(false);
+			return;
+		}
+		ContactId contactId = ctx.getContactId();
+		if (contactId == null) {
+			LOG.warning("Expected contact tag, got rendezvous tag");
+			onReadError(true);
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onReadError(true);
+			return;
+		}
+		connectionRegistry.registerIncomingConnection(contactId, transportId,
+				this);
+		// Start the outgoing session on another thread
+		ioExecutor.execute(() -> runOutgoingSession(contactId));
+		try {
+			// Store any transport properties discovered from the connection
+			transportPropertyManager.addRemotePropertiesFromConnection(
+					contactId, transportId, remote);
+			// Update the connection registry when we receive our priority
+			PriorityHandler handler = p -> connectionRegistry.setPriority(
+					contactId, transportId, this, p);
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+			interruptOutgoingSession();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, true, false);
+		} catch (DbException | IOException e) {
+			logException(LOG, WARNING, e);
+			onReadError(true);
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, true, true);
+		}
+	}
+
+	private void runOutgoingSession(ContactId contactId) {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onWriteError();
+			return;
+		}
+		try {
+			// Create and run the outgoing session
+			SyncSession out = createDuplexOutgoingSession(ctx, writer, null);
+			setOutgoingSession(out);
+			out.run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+		}
+	}
+}
+

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingHandshakeConnection.java

@@ -0,0 +1,93 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingHandshakeConnection extends HandshakeConnection
+		implements Runnable {
+
+	IncomingHandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, handshakeManager, contactExchangeManager,
+				connectionManager, pendingContactId, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctxIn = recogniseTag(reader, transportId);
+		if (ctxIn == null) {
+			LOG.info("Unrecognised tag");
+			onError(false);
+			return;
+		}
+		PendingContactId inPendingContactId = ctxIn.getPendingContactId();
+		if (inPendingContactId == null) {
+			LOG.warning("Expected rendezvous tag, got contact tag");
+			onError(true);
+			return;
+		}
+		// Allocate the outgoing stream context
+		StreamContext ctxOut =
+				allocateStreamContext(pendingContactId, transportId);
+		if (ctxOut == null) {
+			LOG.warning("Could not allocate stream context");
+			onError(true);
+			return;
+		}
+		// Close the connection if it's redundant
+		if (!connectionRegistry.registerConnection(pendingContactId)) {
+			LOG.info("Redundant rendezvous connection");
+			onError(true);
+			return;
+		}
+		// Handshake and exchange contacts
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			// Flush the output stream to send the outgoing stream header
+			StreamWriter out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+			HandshakeResult result =
+					handshakeManager.handshake(pendingContactId, in, out);
+			contactExchangeManager.exchangeContacts(pendingContactId,
+					connection, result.getMasterKey(), result.isAlice(), false);
+			connectionRegistry.unregisterConnection(pendingContactId, true);
+			// Reuse the connection as a transport connection
+			connectionManager.manageIncomingConnection(transportId, connection);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError(true);
+			connectionRegistry.unregisterConnection(pendingContactId, false);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingSimplexSyncConnection.java

@@ -0,0 +1,79 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
+
+	private final TransportId transportId;
+	private final TransportConnectionReader reader;
+
+	IncomingSimplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			TransportId transportId, TransportConnectionReader reader) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.transportId = transportId;
+		this.reader = reader;
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		if (ctx == null) {
+			LOG.info("Unrecognised tag");
+			onError(false);
+			return;
+		}
+		ContactId contactId = ctx.getContactId();
+		if (contactId == null) {
+			LOG.warning("Received rendezvous stream, expected contact");
+			onError(true);
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onError(true);
+			return;
+		}
+		try {
+			// We don't expect to receive a priority for this connection
+			PriorityHandler handler = p ->
+					LOG.info("Ignoring priority for simplex connection");
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError(true);
+		}
+	}
+
+	private void onError(boolean recognised) {
+		disposeOnError(reader, recognised);
+	}
+}
+

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java

@@ -0,0 +1,140 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.security.SecureRandom;
+import java.util.concurrent.Executor;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingDuplexSyncConnection extends DuplexSyncConnection
+		implements Runnable {
+
+	private final SecureRandom secureRandom;
+	private final ContactId contactId;
+
+	OutgoingDuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, SecureRandom secureRandom, ContactId contactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager, ioExecutor, transportId, connection);
+		this.secureRandom = secureRandom;
+		this.contactId = contactId;
+	}
+
+	@Override
+	public void run() {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onWriteError();
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Cannot use handshake mode stream context");
+			onWriteError();
+			return;
+		}
+		// Start the incoming session on another thread
+		Priority priority = generatePriority();
+		ioExecutor.execute(() -> runIncomingSession(priority));
+		try {
+			// Create and run the outgoing session
+			SyncSession out =
+					createDuplexOutgoingSession(ctx, writer, priority);
+			setOutgoingSession(out);
+			out.run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+		}
+	}
+
+	private void runIncomingSession(Priority priority) {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		// Unrecognised tags are suspicious in this case
+		if (ctx == null) {
+			LOG.warning("Unrecognised tag for returning stream");
+			onReadError();
+			return;
+		}
+		// Check that the stream comes from the expected contact
+		ContactId inContactId = ctx.getContactId();
+		if (inContactId == null) {
+			LOG.warning("Expected contact tag, got rendezvous tag");
+			onReadError();
+			return;
+		}
+		if (!contactId.equals(inContactId)) {
+			LOG.warning("Wrong contact ID for returning stream");
+			onReadError();
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onReadError();
+			return;
+		}
+		connectionRegistry.registerOutgoingConnection(contactId, transportId,
+				this, priority);
+		try {
+			// Store any transport properties discovered from the connection
+			transportPropertyManager.addRemotePropertiesFromConnection(
+					contactId, transportId, remote);
+			// We don't expect to receive a priority for this connection
+			PriorityHandler handler = p ->
+					LOG.info("Ignoring priority for outgoing connection");
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+			interruptOutgoingSession();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, false, false);
+		} catch (DbException | IOException e) {
+			logException(LOG, WARNING, e);
+			onReadError();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, false, true);
+		}
+	}
+
+	private void onReadError() {
+		// 'Recognised' is always true for outgoing connections
+		onReadError(true);
+	}
+
+	private Priority generatePriority() {
+		byte[] nonce = new byte[PRIORITY_NONCE_BYTES];
+		secureRandom.nextBytes(nonce);
+		return new Priority(nonce);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingHandshakeConnection.java

@@ -0,0 +1,115 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingHandshakeConnection extends HandshakeConnection
+		implements Runnable {
+
+	OutgoingHandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, handshakeManager, contactExchangeManager,
+				connectionManager, pendingContactId, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Allocate the outgoing stream context
+		StreamContext ctxOut =
+				allocateStreamContext(pendingContactId, transportId);
+		if (ctxOut == null) {
+			LOG.warning("Could not allocate stream context");
+			onError();
+			return;
+		}
+		// Flush the output stream to send the outgoing stream header
+		StreamWriter out;
+		try {
+			out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			return;
+		}
+		// Read and recognise the tag
+		StreamContext ctxIn = recogniseTag(reader, transportId);
+		// Unrecognised tags are suspicious in this case
+		if (ctxIn == null) {
+			LOG.warning("Unrecognised tag for returning stream");
+			onError();
+			return;
+		}
+		// Check that the stream comes from the expected pending contact
+		PendingContactId inPendingContactId = ctxIn.getPendingContactId();
+		if (inPendingContactId == null) {
+			LOG.warning("Expected rendezvous tag, got contact tag");
+			onError();
+			return;
+		}
+		if (!inPendingContactId.equals(pendingContactId)) {
+			LOG.warning("Wrong pending contact ID for returning stream");
+			onError();
+			return;
+		}
+		// Close the connection if it's redundant
+		if (!connectionRegistry.registerConnection(pendingContactId)) {
+			LOG.info("Redundant rendezvous connection");
+			onError();
+			return;
+		}
+		// Handshake and exchange contacts
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			HandshakeResult result =
+					handshakeManager.handshake(pendingContactId, in, out);
+			Contact contact = contactExchangeManager.exchangeContacts(
+					pendingContactId, connection, result.getMasterKey(),
+					result.isAlice(), false);
+			connectionRegistry.unregisterConnection(pendingContactId, true);
+			// Reuse the connection as a transport connection
+			connectionManager.manageOutgoingConnection(contact.getId(),
+					transportId, connection);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			connectionRegistry.unregisterConnection(pendingContactId, false);
+		}
+	}
+
+	private void onError() {
+		// 'Recognised' is always true for outgoing connections
+		onError(true);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingSimplexSyncConnection.java

@@ -0,0 +1,78 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingSimplexSyncConnection extends SyncConnection implements Runnable {
+
+	private final ContactId contactId;
+	private final TransportId transportId;
+	private final TransportConnectionWriter writer;
+
+	OutgoingSimplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			ContactId contactId, TransportId transportId,
+			TransportConnectionWriter writer) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.contactId = contactId;
+		this.transportId = transportId;
+		this.writer = writer;
+	}
+
+	@Override
+	public void run() {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onError();
+			return;
+		}
+		try {
+			// Create and run the outgoing session
+			createSimplexOutgoingSession(ctx, writer).run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError();
+		}
+	}
+
+	private void onError() {
+		disposeOnError(writer);
+	}
+
+	private SyncSession createSimplexOutgoingSession(StreamContext ctx,
+			TransportConnectionWriter w) throws IOException {
+		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
+				w.getOutputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createSimplexOutgoingSession(c,
+				ctx.getTransportId(), w.getMaxLatency(), streamWriter);
+	}
+}
+

bramble-core/src/main/java/org/briarproject/bramble/connection/SyncConnection.java

@@ -0,0 +1,64 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class SyncConnection extends Connection {
+
+	final SyncSessionFactory syncSessionFactory;
+	final TransportPropertyManager transportPropertyManager;
+
+	SyncConnection(KeyManager keyManager, ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory);
+		this.syncSessionFactory = syncSessionFactory;
+		this.transportPropertyManager = transportPropertyManager;
+	}
+
+	@Nullable
+	StreamContext allocateStreamContext(ContactId contactId,
+			TransportId transportId) {
+		try {
+			return keyManager.getStreamContext(contactId, transportId);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	SyncSession createIncomingSession(StreamContext ctx,
+			TransportConnectionReader r, PriorityHandler handler)
+			throws IOException {
+		InputStream streamReader = streamReaderFactory.createStreamReader(
+				r.getInputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory
+				.createIncomingSession(c, streamReader, handler);
+	}
+}

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

@@ -1,709 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.contact.Contact;
-import org.briarproject.bramble.api.contact.ContactExchangeManager;
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.HandshakeManager;
-import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.lifecycle.IoExecutor;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportConnectionReader;
-import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
-import org.briarproject.bramble.api.properties.TransportProperties;
-import org.briarproject.bramble.api.properties.TransportPropertyManager;
-import org.briarproject.bramble.api.sync.SyncSession;
-import org.briarproject.bramble.api.sync.SyncSessionFactory;
-import org.briarproject.bramble.api.transport.KeyManager;
-import org.briarproject.bramble.api.transport.StreamContext;
-import org.briarproject.bramble.api.transport.StreamReaderFactory;
-import org.briarproject.bramble.api.transport.StreamWriter;
-import org.briarproject.bramble.api.transport.StreamWriterFactory;
-
-import java.io.IOException;
-import java.io.InputStream;
-import java.util.concurrent.Executor;
-import java.util.logging.Logger;
-
-import javax.annotation.Nullable;
-import javax.inject.Inject;
-
-import static java.util.logging.Level.WARNING;
-import static java.util.logging.Logger.getLogger;
-import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
-import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENGTH;
-import static org.briarproject.bramble.util.IoUtils.read;
-import static org.briarproject.bramble.util.LogUtils.logException;
-
-@NotNullByDefault
-class ConnectionManagerImpl implements ConnectionManager {
-
-	private static final Logger LOG =
-			getLogger(ConnectionManagerImpl.class.getName());
-
-	private final Executor ioExecutor;
-	private final KeyManager keyManager;
-	private final StreamReaderFactory streamReaderFactory;
-	private final StreamWriterFactory streamWriterFactory;
-	private final SyncSessionFactory syncSessionFactory;
-	private final HandshakeManager handshakeManager;
-	private final ContactExchangeManager contactExchangeManager;
-	private final ConnectionRegistry connectionRegistry;
-	private final TransportPropertyManager transportPropertyManager;
-
-	@Inject
-	ConnectionManagerImpl(@IoExecutor Executor ioExecutor,
-			KeyManager keyManager, StreamReaderFactory streamReaderFactory,
-			StreamWriterFactory streamWriterFactory,
-			SyncSessionFactory syncSessionFactory,
-			HandshakeManager handshakeManager,
-			ContactExchangeManager contactExchangeManager,
-			ConnectionRegistry connectionRegistry,
-			TransportPropertyManager transportPropertyManager) {
-		this.ioExecutor = ioExecutor;
-		this.keyManager = keyManager;
-		this.streamReaderFactory = streamReaderFactory;
-		this.streamWriterFactory = streamWriterFactory;
-		this.syncSessionFactory = syncSessionFactory;
-		this.handshakeManager = handshakeManager;
-		this.contactExchangeManager = contactExchangeManager;
-		this.connectionRegistry = connectionRegistry;
-		this.transportPropertyManager = transportPropertyManager;
-	}
-
-	@Override
-	public void manageIncomingConnection(TransportId t,
-			TransportConnectionReader r) {
-		ioExecutor.execute(new ManageIncomingSimplexConnection(t, r));
-	}
-
-	@Override
-	public void manageIncomingConnection(TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageIncomingDuplexConnection(t, d));
-	}
-
-	@Override
-	public void manageIncomingConnection(PendingContactId p, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageIncomingHandshakeConnection(p, t, d));
-	}
-
-	@Override
-	public void manageOutgoingConnection(ContactId c, TransportId t,
-			TransportConnectionWriter w) {
-		ioExecutor.execute(new ManageOutgoingSimplexConnection(c, t, w));
-	}
-
-	@Override
-	public void manageOutgoingConnection(ContactId c, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageOutgoingDuplexConnection(c, t, d));
-	}
-
-	@Override
-	public void manageOutgoingConnection(PendingContactId p, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageOutgoingHandshakeConnection(p, t, d));
-	}
-
-	private byte[] readTag(InputStream in) throws IOException {
-		byte[] tag = new byte[TAG_LENGTH];
-		read(in, tag);
-		return tag;
-	}
-
-	private SyncSession createIncomingSession(StreamContext ctx,
-			TransportConnectionReader r) throws IOException {
-		InputStream streamReader = streamReaderFactory.createStreamReader(
-				r.getInputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createIncomingSession(c, streamReader);
-	}
-
-	private SyncSession createSimplexOutgoingSession(StreamContext ctx,
-			TransportConnectionWriter w) throws IOException {
-		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
-				w.getOutputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createSimplexOutgoingSession(c,
-				w.getMaxLatency(), streamWriter);
-	}
-
-	private SyncSession createDuplexOutgoingSession(StreamContext ctx,
-			TransportConnectionWriter w) throws IOException {
-		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
-				w.getOutputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createDuplexOutgoingSession(c,
-				w.getMaxLatency(), w.getMaxIdleTime(), streamWriter);
-	}
-
-	private void disposeOnError(TransportConnectionReader reader,
-			boolean recognised) {
-		try {
-			reader.dispose(true, recognised);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void disposeOnError(TransportConnectionWriter writer) {
-		try {
-			writer.dispose(true);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private class ManageIncomingSimplexConnection implements Runnable {
-
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-
-		private ManageIncomingSimplexConnection(TransportId transportId,
-				TransportConnectionReader reader) {
-			this.transportId = transportId;
-			this.reader = reader;
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(false);
-				return;
-			}
-			if (ctx == null) {
-				LOG.info("Unrecognised tag");
-				onError(false);
-				return;
-			}
-			ContactId contactId = ctx.getContactId();
-			if (contactId == null) {
-				LOG.warning("Received rendezvous stream, expected contact");
-				onError(true);
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onError(true);
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId, true);
-			try {
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						true);
-			}
-		}
-
-		private void onError(boolean recognised) {
-			disposeOnError(reader, recognised);
-		}
-	}
-
-	private class ManageOutgoingSimplexConnection implements Runnable {
-
-		private final ContactId contactId;
-		private final TransportId transportId;
-		private final TransportConnectionWriter writer;
-
-		private ManageOutgoingSimplexConnection(ContactId contactId,
-				TransportId transportId, TransportConnectionWriter writer) {
-			this.contactId = contactId;
-			this.transportId = transportId;
-			this.writer = writer;
-		}
-
-		@Override
-		public void run() {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onError();
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId,
-					false);
-			try {
-				// Create and run the outgoing session
-				createSimplexOutgoingSession(ctx, writer).run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError();
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						false);
-			}
-		}
-
-		private void onError() {
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageIncomingDuplexConnection implements Runnable {
-
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-		private final TransportProperties remote;
-
-		@Nullable
-		private volatile SyncSession outgoingSession = null;
-
-		private ManageIncomingDuplexConnection(TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.transportId = transportId;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-			remote = connection.getRemoteProperties();
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onReadError(false);
-				return;
-			}
-			if (ctx == null) {
-				LOG.info("Unrecognised tag");
-				onReadError(false);
-				return;
-			}
-			ContactId contactId = ctx.getContactId();
-			if (contactId == null) {
-				LOG.warning("Expected contact tag, got rendezvous tag");
-				onReadError(true);
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onReadError(true);
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId, true);
-			// Start the outgoing session on another thread
-			ioExecutor.execute(() -> runOutgoingSession(contactId));
-			try {
-				// Store any transport properties discovered from the connection
-				transportPropertyManager.addRemotePropertiesFromConnection(
-						contactId, transportId, remote);
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-				// Interrupt the outgoing session so it finishes cleanly
-				SyncSession out = outgoingSession;
-				if (out != null) out.interrupt();
-			} catch (DbException | IOException e) {
-				logException(LOG, WARNING, e);
-				onReadError(true);
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						true);
-			}
-		}
-
-		private void runOutgoingSession(ContactId contactId) {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onWriteError();
-				return;
-			}
-			try {
-				// Create and run the outgoing session
-				SyncSession out = createDuplexOutgoingSession(ctx, writer);
-				outgoingSession = out;
-				out.run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-			}
-		}
-
-		private void onReadError(boolean recognised) {
-			disposeOnError(reader, recognised);
-			disposeOnError(writer);
-			// Interrupt the outgoing session so it finishes
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
-		}
-
-		private void onWriteError() {
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageOutgoingDuplexConnection implements Runnable {
-
-		private final ContactId contactId;
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-		private final TransportProperties remote;
-
-		@Nullable
-		private volatile SyncSession outgoingSession = null;
-
-		private ManageOutgoingDuplexConnection(ContactId contactId,
-				TransportId transportId, DuplexTransportConnection connection) {
-			this.contactId = contactId;
-			this.transportId = transportId;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-			remote = connection.getRemoteProperties();
-		}
-
-		@Override
-		public void run() {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onWriteError();
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Cannot use handshake mode stream context");
-				onWriteError();
-				return;
-			}
-			// Start the incoming session on another thread
-			ioExecutor.execute(this::runIncomingSession);
-			try {
-				// Create and run the outgoing session
-				SyncSession out = createDuplexOutgoingSession(ctx, writer);
-				outgoingSession = out;
-				out.run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-			}
-		}
-
-		private void runIncomingSession() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onReadError();
-				return;
-			}
-			// Unrecognised tags are suspicious in this case
-			if (ctx == null) {
-				LOG.warning("Unrecognised tag for returning stream");
-				onReadError();
-				return;
-			}
-			// Check that the stream comes from the expected contact
-			ContactId inContactId = ctx.getContactId();
-			if (inContactId == null) {
-				LOG.warning("Expected contact tag, got rendezvous tag");
-				onReadError();
-				return;
-			}
-			if (!contactId.equals(inContactId)) {
-				LOG.warning("Wrong contact ID for returning stream");
-				onReadError();
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onReadError();
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId,
-					false);
-			try {
-				// Store any transport properties discovered from the connection
-				transportPropertyManager.addRemotePropertiesFromConnection(
-						contactId, transportId, remote);
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-				// Interrupt the outgoing session so it finishes cleanly
-				SyncSession out = outgoingSession;
-				if (out != null) out.interrupt();
-			} catch (DbException | IOException e) {
-				logException(LOG, WARNING, e);
-				onReadError();
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						false);
-			}
-		}
-
-		private void onReadError() {
-			// 'Recognised' is always true for outgoing connections
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-			// Interrupt the outgoing session so it finishes
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
-		}
-
-		private void onWriteError() {
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageIncomingHandshakeConnection implements Runnable {
-
-		private final PendingContactId pendingContactId;
-		private final TransportId transportId;
-		private final DuplexTransportConnection connection;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-
-		private ManageIncomingHandshakeConnection(
-				PendingContactId pendingContactId, TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.pendingContactId = pendingContactId;
-			this.transportId = transportId;
-			this.connection = connection;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctxIn;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctxIn = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(false);
-				return;
-			}
-			if (ctxIn == null) {
-				LOG.info("Unrecognised tag");
-				onError(false);
-				return;
-			}
-			PendingContactId inPendingContactId = ctxIn.getPendingContactId();
-			if (inPendingContactId == null) {
-				LOG.warning("Expected rendezvous tag, got contact tag");
-				onError(true);
-				return;
-			}
-			// Allocate the outgoing stream context
-			StreamContext ctxOut;
-			try {
-				ctxOut = keyManager.getStreamContext(pendingContactId,
-						transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-				return;
-			}
-			if (ctxOut == null) {
-				LOG.warning("Could not allocate stream context");
-				onError(true);
-				return;
-			}
-			// Close the connection if it's redundant
-			if (!connectionRegistry.registerConnection(pendingContactId)) {
-				LOG.info("Redundant rendezvous connection");
-				onError(true);
-				return;
-			}
-			// Handshake and exchange contacts
-			try {
-				InputStream in = streamReaderFactory.createStreamReader(
-						reader.getInputStream(), ctxIn);
-				// Flush the output stream to send the outgoing stream header
-				StreamWriter out = streamWriterFactory.createStreamWriter(
-						writer.getOutputStream(), ctxOut);
-				out.getOutputStream().flush();
-				HandshakeResult result = handshakeManager.handshake(
-						pendingContactId, in, out);
-				Contact contact = contactExchangeManager.exchangeContacts(
-						pendingContactId, connection, result.getMasterKey(),
-						result.isAlice(), false);
-				connectionRegistry.unregisterConnection(pendingContactId, true);
-				// Reuse the connection as a transport connection
-				manageOutgoingConnection(contact.getId(), transportId,
-						connection);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-				connectionRegistry.unregisterConnection(pendingContactId,
-						false);
-			}
-		}
-
-		private void onError(boolean recognised) {
-			disposeOnError(reader, recognised);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageOutgoingHandshakeConnection implements Runnable {
-
-		private final PendingContactId pendingContactId;
-		private final TransportId transportId;
-		private final DuplexTransportConnection connection;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-
-		private ManageOutgoingHandshakeConnection(
-				PendingContactId pendingContactId, TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.pendingContactId = pendingContactId;
-			this.transportId = transportId;
-			this.connection = connection;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-		}
-
-		@Override
-		public void run() {
-			// Allocate the outgoing stream context
-			StreamContext ctxOut;
-			try {
-				ctxOut = keyManager.getStreamContext(pendingContactId,
-						transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			if (ctxOut == null) {
-				LOG.warning("Could not allocate stream context");
-				onError();
-				return;
-			}
-			// Flush the output stream to send the outgoing stream header
-			StreamWriter out;
-			try {
-				out = streamWriterFactory.createStreamWriter(
-						writer.getOutputStream(), ctxOut);
-				out.getOutputStream().flush();
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			// Read and recognise the tag
-			StreamContext ctxIn;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctxIn = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			// Unrecognised tags are suspicious in this case
-			if (ctxIn == null) {
-				LOG.warning("Unrecognised tag for returning stream");
-				onError();
-				return;
-			}
-			// Check that the stream comes from the expected pending contact
-			PendingContactId inPendingContactId = ctxIn.getPendingContactId();
-			if (inPendingContactId == null) {
-				LOG.warning("Expected rendezvous tag, got contact tag");
-				onError();
-				return;
-			}
-			if (!inPendingContactId.equals(pendingContactId)) {
-				LOG.warning("Wrong pending contact ID for returning stream");
-				onError();
-				return;
-			}
-			// Close the connection if it's redundant
-			if (!connectionRegistry.registerConnection(pendingContactId)) {
-				LOG.info("Redundant rendezvous connection");
-				onError();
-				return;
-			}
-			// Handshake and exchange contacts
-			try {
-				InputStream in = streamReaderFactory.createStreamReader(
-						reader.getInputStream(), ctxIn);
-				HandshakeResult result = handshakeManager.handshake(
-						pendingContactId, in, out);
-				Contact contact = contactExchangeManager.exchangeContacts(
-						pendingContactId, connection, result.getMasterKey(),
-						result.isAlice(), false);
-				connectionRegistry.unregisterConnection(pendingContactId, true);
-				// Reuse the connection as a transport connection
-				manageOutgoingConnection(contact.getId(), transportId,
-						connection);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				connectionRegistry.unregisterConnection(pendingContactId,
-						false);
-			}
-		}
-
-		private void onError() {
-			// 'Recognised' is always true for outgoing connections
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-}

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

@@ -1,150 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.Multiset;
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-import java.util.logging.Logger;
-
-import javax.annotation.concurrent.GuardedBy;
-import javax.annotation.concurrent.ThreadSafe;
-import javax.inject.Inject;
-
-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 =
-			getLogger(ConnectionRegistryImpl.class.getName());
-
-	private final EventBus eventBus;
-
-	private final Object lock = new Object();
-	@GuardedBy("lock")
-	private final Map<TransportId, Multiset<ContactId>> contactConnections;
-	@GuardedBy("lock")
-	private final Multiset<ContactId> contactCounts;
-	@GuardedBy("lock")
-	private final Set<PendingContactId> connectedPendingContacts;
-
-	@Inject
-	ConnectionRegistryImpl(EventBus eventBus) {
-		this.eventBus = eventBus;
-		contactConnections = new HashMap<>();
-		contactCounts = new Multiset<>();
-		connectedPendingContacts = new HashSet<>();
-	}
-
-	@Override
-	public void registerConnection(ContactId c, TransportId t,
-			boolean incoming) {
-		if (LOG.isLoggable(INFO)) {
-			if (incoming) LOG.info("Incoming connection registered: " + t);
-			else LOG.info("Outgoing connection registered: " + t);
-		}
-		boolean firstConnection = false;
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null) {
-				m = new Multiset<>();
-				contactConnections.put(t, m);
-			}
-			m.add(c);
-			if (contactCounts.add(c) == 1) firstConnection = true;
-		}
-		eventBus.broadcast(new ConnectionOpenedEvent(c, t, incoming));
-		if (firstConnection) {
-			LOG.info("Contact connected");
-			eventBus.broadcast(new ContactConnectedEvent(c));
-		}
-	}
-
-	@Override
-	public void unregisterConnection(ContactId c, TransportId t,
-			boolean incoming) {
-		if (LOG.isLoggable(INFO)) {
-			if (incoming) LOG.info("Incoming connection unregistered: " + t);
-			else LOG.info("Outgoing connection unregistered: " + t);
-		}
-		boolean lastConnection = false;
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null || !m.contains(c))
-				throw new IllegalArgumentException();
-			m.remove(c);
-			if (contactCounts.remove(c) == 0) lastConnection = true;
-		}
-		eventBus.broadcast(new ConnectionClosedEvent(c, t, incoming));
-		if (lastConnection) {
-			LOG.info("Contact disconnected");
-			eventBus.broadcast(new ContactDisconnectedEvent(c));
-		}
-	}
-
-	@Override
-	public Collection<ContactId> getConnectedContacts(TransportId t) {
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null) return Collections.emptyList();
-			List<ContactId> ids = new ArrayList<>(m.keySet());
-			if (LOG.isLoggable(INFO))
-				LOG.info(ids.size() + " contacts connected: " + t);
-			return ids;
-		}
-	}
-
-	@Override
-	public boolean isConnected(ContactId c, TransportId t) {
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			return m != null && m.contains(c);
-		}
-	}
-
-	@Override
-	public boolean isConnected(ContactId c) {
-		synchronized (lock) {
-			return contactCounts.contains(c);
-		}
-	}
-
-	@Override
-	public boolean registerConnection(PendingContactId p) {
-		boolean added;
-		synchronized (lock) {
-			added = connectedPendingContacts.add(p);
-		}
-		if (added) eventBus.broadcast(new RendezvousConnectionOpenedEvent(p));
-		return added;
-	}
-
-	@Override
-	public void unregisterConnection(PendingContactId p, boolean success) {
-		synchronized (lock) {
-			if (!connectedPendingContacts.remove(p))
-				throw new IllegalArgumentException();
-		}
-		eventBus.broadcast(new RendezvousConnectionClosedEvent(p, success));
-	}
-}

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

@@ -1,12 +1,12 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.lifecycle.ServiceException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.PluginConfig;

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

@@ -3,8 +3,6 @@ package org.briarproject.bramble.plugin;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginManager;
 
@@ -29,20 +27,6 @@ public class PluginModule {
 		return new BackoffFactoryImpl();
 	}
 
-	@Provides
-	@Singleton
-	ConnectionManager provideConnectionManager(
-			ConnectionManagerImpl connectionManager) {
-		return connectionManager;
-	}
-
-	@Provides
-	@Singleton
-	ConnectionRegistry provideConnectionRegistry(
-			ConnectionRegistryImpl connectionRegistry) {
-		return connectionRegistry;
-	}
-
 	@Provides
 	@Singleton
 	PluginManager providePluginManager(LifecycleManager lifecycleManager,

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

@@ -1,6 +1,8 @@
 package org.briarproject.bramble.plugin;
 
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactAddedEvent;
 import org.briarproject.bramble.api.db.DbException;
@@ -9,8 +11,6 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
@@ -98,8 +98,8 @@ class PollerImpl implements Poller, EventListener {
 			ConnectionClosedEvent c = (ConnectionClosedEvent) e;
 			// Reschedule polling, the polling interval may have decreased
 			reschedule(c.getTransportId());
-			if (!c.isIncoming()) {
-				// Connect to the disconnected contact
+			// If an outgoing connection failed, try to reconnect
+			if (!c.isIncoming() && c.isException()) {
 				connectToContact(c.getContactId(), c.getTransportId());
 			}
 		} else if (e instanceof ConnectionOpenedEvent) {
@@ -215,7 +215,7 @@ class PollerImpl implements Poller, EventListener {
 			Map<ContactId, TransportProperties> remote =
 					transportPropertyManager.getRemoteProperties(t);
 			Collection<ContactId> connected =
-					connectionRegistry.getConnectedContacts(t);
+					connectionRegistry.getConnectedOrBetterContacts(t);
 			Collection<Pair<TransportProperties, ConnectionHandler>>
 					properties = new ArrayList<>();
 			for (Entry<ContactId, TransportProperties> e : remote.entrySet()) {

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

@@ -3,9 +3,16 @@ package org.briarproject.bramble.plugin.bluetooth;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 
+import static java.util.concurrent.TimeUnit.SECONDS;
+
 @NotNullByDefault
 interface BluetoothConnectionLimiter {
 
+	/**
+	 * How long a connection must remain open before it's considered stable.
+	 */
+	long STABILITY_PERIOD_MS = SECONDS.toMillis(90);
+
 	/**
 	 * Informs the limiter that key agreement has started.
 	 */
@@ -23,17 +30,9 @@ interface BluetoothConnectionLimiter {
 	boolean canOpenContactConnection();
 
 	/**
-	 * Informs the limiter that a contact connection has been opened. The
-	 * limiter may close the new connection if key agreement is in progress.
-	 * <p/>
-	 * Returns false if the limiter has closed the new connection.
+	 * Informs the limiter that the given connection has been opened.
 	 */
-	boolean contactConnectionOpened(DuplexTransportConnection conn);
-
-	/**
-	 * Informs the limiter that a key agreement connection has been opened.
-	 */
-	void keyAgreementConnectionOpened(DuplexTransportConnection conn);
+	void connectionOpened(DuplexTransportConnection conn);
 
 	/**
 	 * Informs the limiter that the given connection has been closed.

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

@@ -1,46 +1,53 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
+import org.briarproject.bramble.api.system.Clock;
 
-import java.io.IOException;
-import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.logging.Level.INFO;
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
 
 @NotNullByDefault
 @ThreadSafe
 class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 
 	private static final Logger LOG =
-			Logger.getLogger(BluetoothConnectionLimiterImpl.class.getName());
+			getLogger(BluetoothConnectionLimiterImpl.class.getName());
+
+	private final EventBus eventBus;
+	private final Clock clock;
 
 	private final Object lock = new Object();
-	// The following are locking: lock
-	private final LinkedList<DuplexTransportConnection> connections =
-			new LinkedList<>();
+	@GuardedBy("lock")
+	private final List<ConnectionRecord> connections = new LinkedList<>();
+	@GuardedBy("lock")
 	private boolean keyAgreementInProgress = false;
+	@GuardedBy("lock")
+	private int connectionLimit = 2;
+
+	BluetoothConnectionLimiterImpl(EventBus eventBus, Clock clock) {
+		this.eventBus = eventBus;
+		this.clock = clock;
+	}
 
 	@Override
 	public void keyAgreementStarted() {
-		List<DuplexTransportConnection> close;
 		synchronized (lock) {
 			keyAgreementInProgress = true;
-			close = new ArrayList<>(connections);
-			connections.clear();
 		}
-		if (LOG.isLoggable(INFO)) {
-			LOG.info("Key agreement started, closing " + close.size() +
-					" connections");
-		}
-		for (DuplexTransportConnection conn : close) tryToClose(conn);
+		LOG.info("Key agreement started");
+		eventBus.broadcast(new CloseSyncConnectionsEvent(ID));
 	}
 
 	@Override
@@ -57,60 +64,81 @@ class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 			if (keyAgreementInProgress) {
 				LOG.info("Can't open contact connection during key agreement");
 				return false;
-			} else {
+			}
+			long now = clock.currentTimeMillis();
+			countStableConnections(now);
+			if (connections.size() < connectionLimit) {
 				LOG.info("Can open contact connection");
 				return true;
-			}
-		}
-	}
-
-	@Override
-	public boolean contactConnectionOpened(DuplexTransportConnection conn) {
-		boolean accept = true;
-		synchronized (lock) {
-			if (keyAgreementInProgress) {
-				LOG.info("Refusing contact connection during key agreement");
-				accept = false;
 			} else {
-				LOG.info("Accepting contact connection");
-				connections.add(conn);
+				LOG.info("Can't open contact connection due to limit");
+				return false;
 			}
 		}
-		if (!accept) tryToClose(conn);
-		return accept;
 	}
 
 	@Override
-	public void keyAgreementConnectionOpened(DuplexTransportConnection conn) {
+	public void connectionOpened(DuplexTransportConnection conn) {
 		synchronized (lock) {
-			LOG.info("Accepting key agreement connection");
-			connections.add(conn);
-		}
-	}
-
-	private void tryToClose(DuplexTransportConnection conn) {
-		try {
-			conn.getWriter().dispose(false);
-			conn.getReader().dispose(false, false);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
+			long now = clock.currentTimeMillis();
+			countStableConnections(now);
+			connections.add(new ConnectionRecord(conn, now));
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Connection opened, " + connections.size() + " open");
+			}
 		}
 	}
 
 	@Override
 	public void connectionClosed(DuplexTransportConnection conn) {
 		synchronized (lock) {
-			connections.remove(conn);
-			if (LOG.isLoggable(INFO))
+			countStableConnections(clock.currentTimeMillis());
+			Iterator<ConnectionRecord> it = connections.iterator();
+			while (it.hasNext()) {
+				if (it.next().conn == conn) {
+					it.remove();
+					break;
+				}
+			}
+			if (LOG.isLoggable(INFO)) {
 				LOG.info("Connection closed, " + connections.size() + " open");
+			}
 		}
 	}
 
 	@Override
 	public void allConnectionsClosed() {
 		synchronized (lock) {
+			long now = clock.currentTimeMillis();
+			countStableConnections(now);
 			connections.clear();
 			LOG.info("All connections closed");
 		}
 	}
+
+	@GuardedBy("lock")
+	private void countStableConnections(long now) {
+		int stable = 0;
+		for (ConnectionRecord rec : connections) {
+			if (now - rec.timeOpened >= STABILITY_PERIOD_MS) stable++;
+		}
+		if (stable > connectionLimit) {
+			connectionLimit = stable;
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Raising connection limit to " + connectionLimit);
+			}
+		}
+	}
+
+	private static class ConnectionRecord {
+
+		private final DuplexTransportConnection conn;
+		private final long timeOpened;
+
+		private ConnectionRecord(DuplexTransportConnection conn,
+				long timeOpened) {
+			this.conn = conn;
+			this.timeOpened = timeOpened;
+		}
+	}
 }

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

@@ -232,10 +232,9 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 				return;
 			}
 			LOG.info("Connection received");
-			if (connectionLimiter.contactConnectionOpened(conn)) {
-				backoff.reset();
-				callback.handleConnection(conn);
-			}
+			connectionLimiter.connectionOpened(conn);
+			backoff.reset();
+			callback.handleConnection(conn);
 			if (!running) return;
 		}
 	}
@@ -327,8 +326,8 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		String uuid = p.get(PROP_UUID);
 		if (isNullOrEmpty(uuid)) return null;
 		DuplexTransportConnection conn = connect(address, uuid);
-		if (conn == null) return null;
-		return connectionLimiter.contactConnectionOpened(conn) ? conn : null;
+		if (conn != null) connectionLimiter.connectionOpened(conn);
+		return conn;
 	}
 
 	@Override
@@ -384,7 +383,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 				LOG.info("Connecting to key agreement UUID " + uuid);
 			conn = connect(address, uuid);
 		}
-		if (conn != null) connectionLimiter.keyAgreementConnectionOpened(conn);
+		if (conn != null) connectionLimiter.connectionOpened(conn);
 		return conn;
 	}
 
@@ -453,7 +452,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		public KeyAgreementConnection accept() throws IOException {
 			DuplexTransportConnection conn = acceptConnection(ss);
 			if (LOG.isLoggable(INFO)) LOG.info(ID + ": Incoming connection");
-			connectionLimiter.keyAgreementConnectionOpened(conn);
+			connectionLimiter.connectionOpened(conn);
 			return new KeyAgreementConnection(conn, ID);
 		}
 

bramble-core/src/main/java/org/briarproject/bramble/rendezvous/RendezvousPollerImpl.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.rendezvous;
 
 import org.briarproject.bramble.PoliteExecutor;
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.contact.PendingContactState;
@@ -23,7 +24,6 @@ import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.lifecycle.ServiceException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;

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

@@ -11,13 +11,16 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.sync.event.GroupVisibilityUpdatedEvent;
 import org.briarproject.bramble.api.sync.event.MessageRequestedEvent;
 import org.briarproject.bramble.api.sync.event.MessageSharedEvent;
@@ -35,6 +38,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -71,9 +75,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private final EventBus eventBus;
 	private final Clock clock;
 	private final ContactId contactId;
+	private final TransportId transportId;
 	private final int maxLatency, maxIdleTime;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
+	@Nullable
+	private final Priority priority;
 	private final BlockingQueue<ThrowingRunnable<IOException>> writerTasks;
 
 	private final AtomicBoolean generateAckQueued = new AtomicBoolean(false);
@@ -86,18 +93,21 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	DuplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, Clock clock, ContactId contactId, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter,
-			SyncRecordWriter recordWriter) {
+			EventBus eventBus, Clock clock, ContactId contactId,
+			TransportId transportId, int maxLatency, int maxIdleTime,
+			StreamWriter streamWriter, SyncRecordWriter recordWriter,
+			@Nullable Priority priority) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.clock = clock;
 		this.contactId = contactId;
+		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.maxIdleTime = maxIdleTime;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
+		this.priority = priority;
 		writerTasks = new LinkedBlockingQueue<>();
 	}
 
@@ -108,6 +118,8 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 		try {
 			// Send our supported protocol versions
 			recordWriter.writeVersions(new Versions(SUPPORTED_VERSIONS));
+			// Send our connection priority, if this is an outgoing connection
+			if (priority != null) recordWriter.writePriority(priority);
 			// Start a query for each type of record
 			generateAck();
 			generateBatch();
@@ -223,6 +235,9 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
+		} else if (e instanceof CloseSyncConnectionsEvent) {
+			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
+			if (c.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

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

@@ -15,6 +15,8 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.SyncSession;
@@ -47,17 +49,19 @@ class IncomingSession implements SyncSession, EventListener {
 	private final EventBus eventBus;
 	private final ContactId contactId;
 	private final SyncRecordReader recordReader;
+	private final PriorityHandler priorityHandler;
 
 	private volatile boolean interrupted = false;
 
 	IncomingSession(DatabaseComponent db, Executor dbExecutor,
 			EventBus eventBus, ContactId contactId,
-			SyncRecordReader recordReader) {
+			SyncRecordReader recordReader, PriorityHandler priorityHandler) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.contactId = contactId;
 		this.recordReader = recordReader;
+		this.priorityHandler = priorityHandler;
 	}
 
 	@IoExecutor
@@ -86,6 +90,9 @@ class IncomingSession implements SyncSession, EventListener {
 				} else if (recordReader.hasVersions()) {
 					Versions v = recordReader.readVersions();
 					dbExecutor.execute(new ReceiveVersions(v));
+				} else if (recordReader.hasPriority()) {
+					Priority p = recordReader.readPriority();
+					priorityHandler.handle(p);
 				} else {
 					// unknown records are ignored in RecordReader#eof()
 					throw new FormatException();

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

@@ -11,11 +11,13 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.IOException;
@@ -56,6 +58,7 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private final Executor dbExecutor;
 	private final EventBus eventBus;
 	private final ContactId contactId;
+	private final TransportId transportId;
 	private final int maxLatency;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
@@ -65,12 +68,14 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	SimplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, ContactId contactId, int maxLatency,
-			StreamWriter streamWriter, SyncRecordWriter recordWriter) {
+			EventBus eventBus, ContactId contactId, TransportId transportId,
+			int maxLatency, StreamWriter streamWriter,
+			SyncRecordWriter recordWriter) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.contactId = contactId;
+		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
@@ -123,6 +128,9 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
+		} else if (e instanceof CloseSyncConnectionsEvent) {
+			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
+			if (c.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

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

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.Versions;
@@ -26,10 +27,12 @@ import javax.annotation.concurrent.NotThreadSafe;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 
 @NotThreadSafe
@@ -48,7 +51,7 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 
 	private static boolean isKnownRecordType(byte type) {
 		return type == ACK || type == MESSAGE || type == OFFER ||
-				type == REQUEST || type == VERSIONS;
+				type == REQUEST || type == VERSIONS || type == PRIORITY;
 	}
 
 	private final MessageFactory messageFactory;
@@ -174,4 +177,23 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 		nextRecord = null;
 		return supported;
 	}
+
+	@Override
+	public boolean hasPriority() throws IOException {
+		return !eof() && getNextRecordType() == PRIORITY;
+	}
+
+	@Override
+	public Priority readPriority() throws IOException {
+		if (!hasPriority()) throw new FormatException();
+		return new Priority(readNonce());
+	}
+
+	private byte[] readNonce() throws IOException {
+		if (nextRecord == null) throw new AssertionError();
+		byte[] payload = nextRecord.getPayload();
+		if (payload.length != PRIORITY_NONCE_BYTES) throw new FormatException();
+		nextRecord = null;
+		return payload;
+	}
 }

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

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.Versions;
@@ -20,6 +21,7 @@ import javax.annotation.concurrent.NotThreadSafe;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
@@ -73,6 +75,12 @@ class SyncRecordWriterImpl implements SyncRecordWriter {
 		writeRecord(VERSIONS);
 	}
 
+	@Override
+	public void writePriority(Priority p) throws IOException {
+		writer.writeRecord(
+				new Record(PROTOCOL_VERSION, PRIORITY, p.getNonce()));
+	}
+
 	@Override
 	public void flush() throws IOException {
 		writer.flush();

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

@@ -5,6 +5,9 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.SyncRecordReaderFactory;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
@@ -18,6 +21,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.concurrent.Executor;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
@@ -46,29 +50,32 @@ class SyncSessionFactoryImpl implements SyncSessionFactory {
 	}
 
 	@Override
-	public SyncSession createIncomingSession(ContactId c, InputStream in) {
+	public SyncSession createIncomingSession(ContactId c, InputStream in,
+			PriorityHandler handler) {
 		SyncRecordReader recordReader =
 				recordReaderFactory.createRecordReader(in);
-		return new IncomingSession(db, dbExecutor, eventBus, c, recordReader);
+		return new IncomingSession(db, dbExecutor, eventBus, c, recordReader,
+				handler);
 	}
 
 	@Override
-	public SyncSession createSimplexOutgoingSession(ContactId c,
+	public SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
 			int maxLatency, StreamWriter streamWriter) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c,
+		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c, t,
 				maxLatency, streamWriter, recordWriter);
 	}
 
 	@Override
-	public SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter) {
+	public SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, int maxIdleTime, StreamWriter streamWriter,
+			@Nullable Priority priority) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c,
-				maxLatency, maxIdleTime, streamWriter, recordWriter);
+		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c, t,
+				maxLatency, maxIdleTime, streamWriter, recordWriter, priority);
 	}
 }

bramble-core/src/test/java/org/briarproject/bramble/connection/ConnectionRegistryImplTest.java

@@ -0,0 +1,611 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.jmock.Expectations;
+import org.junit.Test;
+
+import java.util.Collection;
+
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
+import static org.briarproject.bramble.test.TestUtils.getContactId;
+import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.test.TestUtils.getTransportId;
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+public class ConnectionRegistryImplTest extends BrambleMockTestCase {
+
+	private final EventBus eventBus = context.mock(EventBus.class);
+	private final PluginConfig pluginConfig = context.mock(PluginConfig.class);
+	private final InterruptibleConnection conn1 =
+			context.mock(InterruptibleConnection.class, "conn1");
+	private final InterruptibleConnection conn2 =
+			context.mock(InterruptibleConnection.class, "conn2");
+	private final InterruptibleConnection conn3 =
+			context.mock(InterruptibleConnection.class, "conn3");
+
+	private final ContactId contactId1 = getContactId();
+	private final ContactId contactId2 = getContactId();
+	private final TransportId transportId1 = getTransportId();
+	private final TransportId transportId2 = getTransportId();
+	private final TransportId transportId3 = getTransportId();
+	private final PendingContactId pendingContactId =
+			new PendingContactId(getRandomId());
+
+	private final Priority low =
+			new Priority(fromHexString("00000000000000000000000000000000"));
+	private final Priority high =
+			new Priority(fromHexString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"));
+
+	@Test
+	public void testRegisterMultipleConnections() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// The registry should be empty
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedContacts(transportId3));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId3));
+		assertFalse(c.isConnected(contactId1));
+		assertFalse(c.isConnected(contactId1, transportId1));
+		assertFalse(c.isConnected(contactId1, transportId2));
+		assertFalse(c.isConnected(contactId1, transportId3));
+
+		// Check that a registered connection shows up - this should
+		// broadcast a ConnectionOpenedEvent and a ContactConnectedEvent
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Register another connection with the same contact and transport -
+		// this should broadcast a ConnectionOpenedEvent and lookup should be
+		// unaffected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Unregister one of the connections - this should broadcast a
+		// ConnectionClosedEvent and lookup should be unaffected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn1, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Unregister the other connection - this should broadcast a
+		// ConnectionClosedEvent and a ContactDisconnectedEvent
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(
+					ContactDisconnectedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn2, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId1));
+		assertFalse(c.isConnected(contactId1));
+		assertFalse(c.isConnected(contactId1, transportId1));
+
+		// Try to unregister the connection again - exception should be thrown
+		try {
+			c.unregisterConnection(contactId1, transportId1, conn2,
+					true, false);
+			fail();
+		} catch (IllegalArgumentException expected) {
+			// Expected
+		}
+	}
+
+	@Test
+	public void testRegisterMultipleContacts() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register two contacts with one transport, then one of the contacts
+		// with a second transport - this should broadcast three
+		// ConnectionOpenedEvents and two ContactConnectedEvents
+		context.checking(new Expectations() {{
+			exactly(3).of(eventBus).broadcast(with(any(
+					ConnectionOpenedEvent.class)));
+			exactly(2).of(eventBus).broadcast(with(any(
+					ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		c.registerIncomingConnection(contactId2, transportId1, conn2);
+		c.registerIncomingConnection(contactId2, transportId2, conn3);
+		context.assertIsSatisfied();
+
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId2));
+
+		assertTrue(c.isConnected(contactId1, transportId1));
+		assertFalse(c.isConnected(contactId1, transportId2));
+
+		assertTrue(c.isConnected(contactId2, transportId1));
+		assertTrue(c.isConnected(contactId2, transportId2));
+
+		Collection<ContactId> connected = c.getConnectedContacts(transportId1);
+		assertEquals(2, connected.size());
+		assertTrue(connected.contains(contactId1));
+		assertTrue(connected.contains(contactId2));
+
+		connected = c.getConnectedOrBetterContacts(transportId1);
+		assertEquals(2, connected.size());
+		assertTrue(connected.contains(contactId1));
+		assertTrue(connected.contains(contactId2));
+
+		assertEquals(singletonList(contactId2),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId2),
+				c.getConnectedOrBetterContacts(transportId2));
+	}
+
+	@Test
+	public void testConnectionsAreNotInterruptedUnlessPriorityIsSet() {
+		// Prefer transport 2 to transport 1
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId1, singletonList(transportId2))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (worse than 2) with no priority set
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (better than 1) and set priority to high -
+		// the old connection should not be interrupted, despite using a worse
+		// transport, to remain compatible with old peers
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to high -
+		// again, no interruptions are expected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testNewConnectionIsInterruptedIfOldConnectionUsesBetterTransport() {
+		// Prefer transport 1 to transport 2
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId2, singletonList(transportId1))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (better than 2) and set priority to low
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// The contact is not connected via transport 2 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (worse than 1) and set priority to high -
+		// the new connection should be interrupted because it uses a worse
+		// transport
+		context.checking(new Expectations() {{
+			oneOf(conn2).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to low -
+		// no further interruptions
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+
+		// Unregister the interrupted connection (transport 2)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId2, conn2, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// The contact is not connected via transport 2 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testOldConnectionIsInterruptedIfNewConnectionUsesBetterTransport() {
+		// Prefer transport 2 to transport 1
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId1, singletonList(transportId2))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (worse than 2) and set priority to high
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (better than 1) and set priority to low -
+		// the old connection should be interrupted because it uses a worse
+		// transport
+		context.checking(new Expectations() {{
+			oneOf(conn1).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to high -
+		// no further interruptions
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+
+		// Unregister the interrupted connection (transport 1)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn1, true, false);
+		context.assertIsSatisfied();
+
+		// The contact is not connected via transport 1 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testNewConnectionIsInterruptedIfOldConnectionHasHigherPriority() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register a connection with high priority
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register another connection via the same transport (no priority yet)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Set the priority of the second connection to low - the second
+		// connection should be interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn2).interruptOutgoingSession();
+		}});
+		c.setPriority(contactId1, transportId1, conn2, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register a third connection with low priority - it should also be
+		// interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn3).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn3, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+	}
+
+	@Test
+	public void testOldConnectionIsInterruptedIfNewConnectionHasHigherPriority() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register a connection with low priority
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register another connection via the same transport (no priority yet)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Set the priority of the second connection to high - the first
+		// connection should be interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn1).interruptOutgoingSession();
+		}});
+		c.setPriority(contactId1, transportId1, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+	}
+
+	@Test
+	public void testRegisterAndUnregisterPendingContacts() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(
+					RendezvousConnectionOpenedEvent.class)));
+		}});
+		assertTrue(c.registerConnection(pendingContactId));
+		assertFalse(c.registerConnection(pendingContactId)); // Redundant
+		context.assertIsSatisfied();
+
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(
+					RendezvousConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(pendingContactId, true);
+		context.assertIsSatisfied();
+
+		try {
+			c.unregisterConnection(pendingContactId, true);
+			fail();
+		} catch (IllegalArgumentException expected) {
+			// Expected
+		}
+	}
+}

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

@@ -2,13 +2,13 @@ package org.briarproject.bramble.contact;
 
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
 import org.briarproject.bramble.BrambleCoreModule;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
 
 import java.util.concurrent.Executor;

bramble-core/src/test/java/org/briarproject/bramble/plugin/ConnectionRegistryImplTest.java

@@ -1,149 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-import org.briarproject.bramble.test.BrambleMockTestCase;
-import org.jmock.Expectations;
-import org.junit.Test;
-
-import java.util.Collection;
-
-import static java.util.Collections.emptyList;
-import static java.util.Collections.singletonList;
-import static org.briarproject.bramble.test.TestUtils.getContactId;
-import static org.briarproject.bramble.test.TestUtils.getRandomId;
-import static org.briarproject.bramble.test.TestUtils.getTransportId;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
-
-public class ConnectionRegistryImplTest extends BrambleMockTestCase {
-
-	private final EventBus eventBus = context.mock(EventBus.class);
-
-	private final ContactId contactId = getContactId();
-	private final ContactId contactId1 = getContactId();
-	private final TransportId transportId = getTransportId();
-	private final TransportId transportId1 = getTransportId();
-	private final PendingContactId pendingContactId =
-			new PendingContactId(getRandomId());
-
-	@Test
-	public void testRegisterAndUnregister() {
-		ConnectionRegistry c = new ConnectionRegistryImpl(eventBus);
-
-		// The registry should be empty
-		assertEquals(emptyList(), c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-
-		// Check that a registered connection shows up - this should
-		// broadcast a ConnectionOpenedEvent and a ContactConnectedEvent
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
-			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Register an identical connection - this should broadcast a
-		// ConnectionOpenedEvent and lookup should be unaffected
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Unregister one of the connections - this should broadcast a
-		// ConnectionClosedEvent and lookup should be unaffected
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
-		}});
-		c.unregisterConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Unregister the other connection - this should broadcast a
-		// ConnectionClosedEvent and a ContactDisconnectedEvent
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
-			oneOf(eventBus).broadcast(with(any(
-					ContactDisconnectedEvent.class)));
-		}});
-		c.unregisterConnection(contactId, transportId, true);
-		assertEquals(emptyList(), c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Try to unregister the connection again - exception should be thrown
-		try {
-			c.unregisterConnection(contactId, transportId, true);
-			fail();
-		} catch (IllegalArgumentException expected) {
-			// Expected
-		}
-
-		// Register both contacts with one transport, one contact with both -
-		// this should broadcast three ConnectionOpenedEvents and two
-		// ContactConnectedEvents
-		context.checking(new Expectations() {{
-			exactly(3).of(eventBus).broadcast(with(any(
-					ConnectionOpenedEvent.class)));
-			exactly(2).of(eventBus).broadcast(with(any(
-					ContactConnectedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		c.registerConnection(contactId1, transportId, true);
-		c.registerConnection(contactId1, transportId1, true);
-		Collection<ContactId> connected = c.getConnectedContacts(transportId);
-		assertEquals(2, connected.size());
-		assertTrue(connected.contains(contactId));
-		assertTrue(connected.contains(contactId1));
-		assertEquals(singletonList(contactId1),
-				c.getConnectedContacts(transportId1));
-	}
-
-	@Test
-	public void testRegisterAndUnregisterPendingContacts() {
-		ConnectionRegistry c = new ConnectionRegistryImpl(eventBus);
-
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(
-					RendezvousConnectionOpenedEvent.class)));
-		}});
-		assertTrue(c.registerConnection(pendingContactId));
-		assertFalse(c.registerConnection(pendingContactId)); // Redundant
-		context.assertIsSatisfied();
-
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(
-					RendezvousConnectionClosedEvent.class)));
-		}});
-		c.unregisterConnection(pendingContactId, true);
-		context.assertIsSatisfied();
-
-		try {
-			c.unregisterConnection(pendingContactId, true);
-			fail();
-		} catch (IllegalArgumentException expected) {
-			// Expected
-		}
-	}
-}

bramble-core/src/test/java/org/briarproject/bramble/plugin/PluginManagerImplTest.java

@@ -1,7 +1,7 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginException;

bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java

@@ -1,10 +1,10 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactAddedEvent;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
@@ -157,7 +157,21 @@ public class PollerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testRescheduleAndReconnectOnConnectionClosed()
+	public void testRescheduleOnOutgoingConnectionClosed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				false, false));
+	}
+
+	@Test
+	public void testRescheduleAndReconnectOnOutgoingConnectionFailed()
 			throws Exception {
 		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
 		DuplexTransportConnection duplexConnection =
@@ -166,45 +180,40 @@ public class PollerImplTest extends BrambleMockTestCase {
 		context.checking(new Expectations() {{
 			allowing(plugin).getId();
 			will(returnValue(transportId));
-			// reschedule()
-			// Get the plugin
-			oneOf(pluginManager).getPlugin(transportId);
-			will(returnValue(plugin));
-			// The plugin supports polling
-			oneOf(plugin).shouldPoll();
-			will(returnValue(true));
-			// Get the plugin
-			oneOf(pluginManager).getPlugin(transportId);
-			will(returnValue(plugin));
-			// The plugin supports polling
-			oneOf(plugin).shouldPoll();
-			will(returnValue(true));
-			// Schedule the next poll
-			oneOf(plugin).getPollingInterval();
-			will(returnValue(pollingInterval));
-			oneOf(clock).currentTimeMillis();
-			will(returnValue(now));
-			oneOf(scheduler).schedule(with(any(Runnable.class)),
-					with((long) pollingInterval), with(MILLISECONDS));
-			will(returnValue(future));
-			// connectToContact()
-			// Check whether the contact is already connected
-			oneOf(connectionRegistry).isConnected(contactId, transportId);
-			will(returnValue(false));
-			// Get the transport properties
-			oneOf(transportPropertyManager).getRemoteProperties(contactId,
-					transportId);
-			will(returnValue(properties));
-			// Connect to the contact
-			oneOf(plugin).createConnection(properties);
-			will(returnValue(duplexConnection));
-			// Pass the connection to the connection manager
-			oneOf(connectionManager).manageOutgoingConnection(contactId,
-					transportId, duplexConnection);
 		}});
+		expectReschedule(plugin);
+		expectReconnect(plugin, duplexConnection);
 
 		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
-				false));
+				false, true));
+	}
+
+	@Test
+	public void testRescheduleOnIncomingConnectionClosed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				true, false));
+	}
+
+	@Test
+	public void testRescheduleOnIncomingConnectionFailed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				true, false));
 	}
 
 	@Test
@@ -354,7 +363,7 @@ public class PollerImplTest extends BrambleMockTestCase {
 			// Get the transport properties and connected contacts
 			oneOf(transportPropertyManager).getRemoteProperties(transportId);
 			will(returnValue(singletonMap(contactId, properties)));
-			oneOf(connectionRegistry).getConnectedContacts(transportId);
+			oneOf(connectionRegistry).getConnectedOrBetterContacts(transportId);
 			will(returnValue(emptyList()));
 			// Poll the plugin
 			oneOf(plugin).poll(with(collectionOf(
@@ -397,7 +406,7 @@ public class PollerImplTest extends BrambleMockTestCase {
 			// Get the transport properties and connected contacts
 			oneOf(transportPropertyManager).getRemoteProperties(transportId);
 			will(returnValue(singletonMap(contactId, properties)));
-			oneOf(connectionRegistry).getConnectedContacts(transportId);
+			oneOf(connectionRegistry).getConnectedOrBetterContacts(transportId);
 			will(returnValue(singletonList(contactId)));
 			// All contacts are connected, so don't poll the plugin
 		}});
@@ -431,4 +440,48 @@ public class PollerImplTest extends BrambleMockTestCase {
 		poller.eventOccurred(new TransportEnabledEvent(transportId));
 		poller.eventOccurred(new TransportDisabledEvent(transportId));
 	}
+
+	private void expectReschedule(Plugin plugin) {
+		context.checking(new Expectations() {{
+			// Get the plugin
+			oneOf(pluginManager).getPlugin(transportId);
+			will(returnValue(plugin));
+			// The plugin supports polling
+			oneOf(plugin).shouldPoll();
+			will(returnValue(true));
+			// Schedule the next poll
+			oneOf(plugin).getPollingInterval();
+			will(returnValue(pollingInterval));
+			oneOf(clock).currentTimeMillis();
+			will(returnValue(now));
+			oneOf(scheduler).schedule(with(any(Runnable.class)),
+					with((long) pollingInterval), with(MILLISECONDS));
+			will(returnValue(future));
+		}});
+	}
+
+	private void expectReconnect(DuplexPlugin plugin,
+			DuplexTransportConnection duplexConnection) throws Exception {
+		context.checking(new Expectations() {{
+			// Get the plugin
+			oneOf(pluginManager).getPlugin(transportId);
+			will(returnValue(plugin));
+			// The plugin supports polling
+			oneOf(plugin).shouldPoll();
+			will(returnValue(true));
+			// Check whether the contact is already connected
+			oneOf(connectionRegistry).isConnected(contactId, transportId);
+			will(returnValue(false));
+			// Get the transport properties
+			oneOf(transportPropertyManager).getRemoteProperties(contactId,
+					transportId);
+			will(returnValue(properties));
+			// Connect to the contact
+			oneOf(plugin).createConnection(properties);
+			will(returnValue(duplexConnection));
+			// Pass the connection to the connection manager
+			oneOf(connectionManager).manageOutgoingConnection(contactId,
+					transportId, duplexConnection);
+		}});
+	}
 }

bramble-core/src/test/java/org/briarproject/bramble/rendezvous/RendezvousPollerImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.rendezvous;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.contact.PendingContactState;
 import org.briarproject.bramble.api.contact.event.PendingContactAddedEvent;
@@ -13,7 +14,6 @@ import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;

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

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
@@ -23,6 +24,7 @@ import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.test.TestUtils.getContactId;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
 public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
@@ -36,14 +38,15 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
 	private final Executor dbExecutor = new ImmediateExecutor();
 	private final ContactId contactId = getContactId();
+	private final TransportId transportId = getTransportId();
 	private final Message message = getMessage(new GroupId(getRandomId()));
 	private final MessageId messageId = message.getId();
 
 	@Test
 	public void testNothingToSend() throws Exception {
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
-				recordWriter);
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				streamWriter, recordWriter);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
@@ -76,8 +79,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 	public void testSomethingToSend() throws Exception {
 		Ack ack = new Ack(singletonList(messageId));
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
-				recordWriter);
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				streamWriter, recordWriter);
 		Transaction ackTxn = new Transaction(null, false);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction msgTxn = new Transaction(null, false);

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

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.record.RecordReader;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.Versions;
@@ -24,11 +25,14 @@ import javax.annotation.Nullable;
 import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -119,6 +123,31 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		reader.readVersions();
 	}
 
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfPriorityNonceIsTooSmall()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES - 1));
+
+		reader.readPriority();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfPriorityNonceIsTooLarge()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES + 1));
+
+		reader.readPriority();
+	}
+
+	@Test
+	public void testNoFormatExceptionIfPriorityNonceIsCorrectSize()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES));
+
+		Priority priority = reader.readPriority();
+		assertEquals(PRIORITY_NONCE_BYTES, priority.getNonce().length);
+	}
+
 	@Test
 	public void testEofReturnsTrueWhenAtEndOfStream() throws Exception {
 		expectReadRecord(createAck());
@@ -173,6 +202,11 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		return new Record(PROTOCOL_VERSION, VERSIONS, payload);
 	}
 
+	private Record createPriority(int nonceBytes) {
+		byte[] payload = getRandomBytes(nonceBytes);
+		return new Record(PROTOCOL_VERSION, PRIORITY, payload);
+	}
+
 	private byte[] createPayload() throws Exception {
 		ByteArrayOutputStream payload = new ByteArrayOutputStream();
 		while (payload.size() + UniqueId.LENGTH <= MAX_RECORD_PAYLOAD_BYTES) {

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

@@ -10,12 +10,15 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 
 import javax.annotation.Nullable;
 
 import dagger.Module;
 import dagger.Provides;
 
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
 import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
@@ -85,6 +88,12 @@ public class TestPluginConfigModule {
 			public boolean shouldPoll() {
 				return false;
 			}
+
+			@Override
+			public Map<TransportId, List<TransportId>> getTransportPreferences() {
+				return emptyMap();
+			}
+
 		};
 		return pluginConfig;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/DesktopPluginModule.java

@@ -6,10 +6,14 @@ import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
+import org.briarproject.bramble.api.plugin.BluetoothConstants;
+import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reliability.ReliabilityLayerFactory;
+import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.plugin.bluetooth.JavaBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.modem.ModemPluginFactory;
 import org.briarproject.bramble.plugin.tcp.LanTcpPluginFactory;
@@ -17,6 +21,8 @@ import org.briarproject.bramble.plugin.tcp.WanTcpPluginFactory;
 
 import java.security.SecureRandom;
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 import java.util.concurrent.Executor;
 
 import dagger.Module;
@@ -24,6 +30,8 @@ import dagger.Provides;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 
 @Module
 public class DesktopPluginModule extends PluginModule {
@@ -32,10 +40,11 @@ public class DesktopPluginModule extends PluginModule {
 	PluginConfig getPluginConfig(@IoExecutor Executor ioExecutor,
 			SecureRandom random, BackoffFactory backoffFactory,
 			ReliabilityLayerFactory reliabilityFactory,
-			ShutdownManager shutdownManager, EventBus eventBus,
+			ShutdownManager shutdownManager, EventBus eventBus, Clock clock,
 			TimeoutMonitor timeoutMonitor) {
 		DuplexPluginFactory bluetooth = new JavaBluetoothPluginFactory(
-				ioExecutor, random, eventBus, timeoutMonitor, backoffFactory);
+				ioExecutor, random, eventBus, clock, timeoutMonitor,
+				backoffFactory);
 		DuplexPluginFactory modem = new ModemPluginFactory(ioExecutor,
 				reliabilityFactory);
 		DuplexPluginFactory lan = new LanTcpPluginFactory(ioExecutor,
@@ -61,6 +70,13 @@ public class DesktopPluginModule extends PluginModule {
 			public boolean shouldPoll() {
 				return true;
 			}
+
+			@Override
+			public Map<TransportId, List<TransportId>> getTransportPreferences() {
+				// Prefer LAN to Bluetooth
+				return singletonMap(BluetoothConstants.ID,
+						singletonList(LanTcpConstants.ID));
+			}
 		};
 		return pluginConfig;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothPluginFactory.java

@@ -9,6 +9,7 @@ import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.system.Clock;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
@@ -30,15 +31,17 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	private final Executor ioExecutor;
 	private final SecureRandom secureRandom;
 	private final EventBus eventBus;
+	private final Clock clock;
 	private final TimeoutMonitor timeoutMonitor;
 	private final BackoffFactory backoffFactory;
 
 	public JavaBluetoothPluginFactory(Executor ioExecutor,
-			SecureRandom secureRandom, EventBus eventBus,
+			SecureRandom secureRandom, EventBus eventBus, Clock clock,
 			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
 		this.secureRandom = secureRandom;
 		this.eventBus = eventBus;
+		this.clock = clock;
 		this.timeoutMonitor = timeoutMonitor;
 		this.backoffFactory = backoffFactory;
 	}
@@ -56,7 +59,7 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl();
+				new BluetoothConnectionLimiterImpl(eventBus, clock);
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		JavaBluetoothPlugin plugin = new JavaBluetoothPlugin(connectionLimiter,

briar-android/src/androidTestScreenshot/java/org/briarproject/briar/android/ScreenshotTest.java

@@ -3,7 +3,7 @@ package org.briarproject.briar.android;
 import android.app.Activity;
 import android.util.Log;
 
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.briar.api.test.TestDataCreator;
 import org.junit.ClassRule;

briar-android/src/androidTestScreenshot/java/org/briarproject/briar/android/SetupDataTest.java

@@ -120,7 +120,8 @@ public class SetupDataTest extends ScreenshotTest {
 
 		// TODO add messages
 
-		connectionRegistry.registerConnection(bob.getId(), ID, true);
+		connectionRegistry.registerIncomingConnection(bob.getId(), ID, () -> {
+		});
 	}
 
 }

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -7,6 +7,7 @@ import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.account.BriarAccountModule;
 import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.account.AccountManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
@@ -19,7 +20,6 @@ import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.api.keyagreement.PayloadParser;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.settings.SettingsManager;
 import org.briarproject.bramble.api.system.AndroidExecutor;

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -20,7 +20,10 @@ import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
+import org.briarproject.bramble.api.plugin.BluetoothConstants;
+import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reporting.DevConfig;
@@ -48,6 +51,8 @@ import java.io.File;
 import java.security.GeneralSecurityException;
 import java.security.SecureRandom;
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
 
@@ -62,6 +67,8 @@ import static android.content.Context.MODE_PRIVATE;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.reporting.ReportingConstants.DEV_ONION_ADDRESS;
 import static org.briarproject.bramble.api.reporting.ReportingConstants.DEV_PUBLIC_KEY_HEX;
 import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
@@ -153,6 +160,13 @@ public class AppModule {
 			public boolean shouldPoll() {
 				return true;
 			}
+
+			@Override
+			public Map<TransportId, List<TransportId>> getTransportPreferences() {
+				// Prefer LAN to Bluetooth
+				return singletonMap(BluetoothConstants.ID,
+						singletonList(LanTcpConstants.ID));
+			}
 		};
 		return pluginConfig;
 	}

briar-android/src/main/java/org/briarproject/briar/android/contact/ContactListFragment.java

@@ -10,6 +10,7 @@ import android.widget.TextView;
 import com.google.android.material.floatingactionbutton.FloatingActionButton;
 import com.google.android.material.snackbar.Snackbar;
 
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
@@ -24,7 +25,6 @@ import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
 import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
 import org.briarproject.briar.R;

briar-android/src/main/java/org/briarproject/briar/android/controller/SharingControllerImpl.java

@@ -1,11 +1,11 @@
 package org.briarproject.briar.android.controller;
 
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
 import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
 

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationActivity.java

@@ -21,6 +21,7 @@ import com.google.android.material.snackbar.Snackbar;
 
 import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
@@ -33,7 +34,6 @@ import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
 import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
 import org.briarproject.bramble.api.sync.ClientId;

briar-android/src/main/java/org/briarproject/briar/android/introduction/ContactChooserFragment.java

@@ -5,13 +5,13 @@ import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.contact.BaseContactListAdapter.OnContactClickListener;

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/ContactExchangeViewModel.java

@@ -2,6 +2,7 @@ package org.briarproject.briar.android.keyagreement;
 
 import android.app.Application;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.crypto.SecretKey;
@@ -10,7 +11,6 @@ import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 

briar-android/src/main/java/org/briarproject/briar/android/privategroup/memberlist/GroupMemberListControllerImpl.java

@@ -1,10 +1,10 @@
 package org.briarproject.briar.android.privategroup.memberlist;
 
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.briar.android.controller.DbControllerImpl;
 import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;

briar-android/src/main/java/org/briarproject/briar/android/sharing/SharingStatusActivity.java

@@ -5,6 +5,7 @@ import android.os.Bundle;
 import android.view.MenuItem;
 import android.widget.TextView;
 
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
@@ -13,7 +14,6 @@ import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.event.GroupRemovedEvent;
 import org.briarproject.briar.R;

briar-core/src/test/java/org/briarproject/briar/messaging/SimplexMessagingIntegrationTestComponent.java

@@ -2,11 +2,11 @@ package org.briarproject.briar.messaging;
 
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
 import org.briarproject.bramble.BrambleCoreModule;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
 import org.briarproject.briar.api.messaging.MessagingManager;
 import org.briarproject.briar.api.messaging.PrivateMessageFactory;

briar-core/src/test/java/org/briarproject/briar/test/BriarIntegrationTestComponent.java

@@ -3,13 +3,13 @@ package org.briarproject.briar.test;
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
 import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.AuthorFactory;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
 import org.briarproject.briar.api.blog.BlogFactory;

briar-headless/src/main/java/org/briarproject/briar/headless/HeadlessModule.kt

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.lifecycle.IoExecutor
 import org.briarproject.bramble.api.network.NetworkManager
 import org.briarproject.bramble.api.plugin.BackoffFactory
 import org.briarproject.bramble.api.plugin.PluginConfig
+import org.briarproject.bramble.api.plugin.TransportId
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory
 import org.briarproject.bramble.api.system.Clock
@@ -88,6 +89,7 @@ internal class HeadlessModule(private val appDir: File) {
             override fun getDuplexFactories(): Collection<DuplexPluginFactory> = duplex
             override fun getSimplexFactories(): Collection<SimplexPluginFactory> = emptyList()
             override fun shouldPoll(): Boolean = true
+            override fun getTransportPreferences(): Map<TransportId, List<TransportId>> = emptyMap()
         }
     }
 

briar-headless/src/test/java/org/briarproject/briar/headless/HeadlessTestModule.kt

@@ -6,6 +6,7 @@ import dagger.Provides
 import org.briarproject.bramble.api.FeatureFlags
 import org.briarproject.bramble.api.db.DatabaseConfig
 import org.briarproject.bramble.api.plugin.PluginConfig
+import org.briarproject.bramble.api.plugin.TransportId
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory
 import org.briarproject.bramble.network.JavaNetworkModule
@@ -55,6 +56,7 @@ internal class HeadlessTestModule(private val appDir: File) {
             override fun getDuplexFactories(): Collection<DuplexPluginFactory> = emptyList()
             override fun getSimplexFactories(): Collection<SimplexPluginFactory> = emptyList()
             override fun shouldPoll(): Boolean = false
+            override fun getTransportPreferences(): Map<TransportId, List<TransportId>> = emptyMap()
         }
     }