New retransmission mechanism, which does away with the need for bundle IDs and should cope better with high bandwidth-delay product links.

api/net/sf/briar/api/protocol/BundleId.java

@@ -1,26 +0,0 @@
-package net.sf.briar.api.protocol;
-
-import java.util.Arrays;
-
-/**
- * Type-safe wrapper for a byte array that uniquely identifies a bundle of
- * acknowledgements, subscriptions, and batches of messages.
- */
-public class BundleId extends UniqueId {
-
-	public static final BundleId NONE = new BundleId(new byte[] {
-			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-	});
-
-	public BundleId(byte[] id) {
-		super(id);
-	}
-
-	@Override
-	public boolean equals(Object o) {
-		if(o instanceof BundleId)
-			return Arrays.equals(id, ((BundleId) o).id);
-		return false;
-	}
-}

api/net/sf/briar/api/protocol/BundleWriter.java

@@ -13,8 +13,8 @@ public interface BundleWriter {
 	/** Returns the bundle's remaining capacity in bytes. */
 	long getRemainingCapacity() throws IOException;
 
-	/** Adds a header to the bundle and returns its identifier. */
+	/** Adds a header to the bundle. */
-	BundleId addHeader(Iterable<BatchId> acks, Iterable<GroupId> subs,
+	void addHeader(Iterable<BatchId> acks, Iterable<GroupId> subs,
 			Map<String, String> transports) throws IOException,
 			GeneralSecurityException;
 

api/net/sf/briar/api/protocol/Header.java

@@ -8,9 +8,6 @@ public interface Header {
 
 	static final int MAX_SIZE = 1024 * 1024;
 
-	// FIXME: Remove BundleId when refactoring is complete
-	BundleId getId();
-
 	/** Returns the acknowledgements contained in the header. */
 	Set<BatchId> getAcks();
 

components/net/sf/briar/db/Database.java

@@ -9,7 +9,6 @@ import net.sf.briar.api.db.DbException;
 import net.sf.briar.api.db.Status;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Message;
 import net.sf.briar.api.protocol.MessageId;
@@ -35,14 +34,10 @@ import net.sf.briar.api.protocol.MessageId;
 interface Database<T> {
 
 	/**
-	 * A batch sent to a contact is considered lost when this many bundles have
+	 * A batch sent to a contact is considered lost when this many more
-	 * been received from the contact since the batch was sent.
+	 * recently sent batches have been acknowledged.
-	 * <p>
-	 * FIXME: Come up with a better retransmission scheme. This scheme doesn't
-	 * cope well with transports that have high latency but send bundles
-	 * frequently.
 	 */
-	static final int RETRANSMIT_THRESHOLD = 3;
+	static final int RETRANSMIT_THRESHOLD = 5;
 
 	/**
 	 * Opens the database.
@@ -103,15 +98,6 @@ interface Database<T> {
 	 */
 	void addOutstandingBatch(T txn, ContactId c, BatchId b, Set<MessageId> sent) throws DbException;
 
-	/**
-	 * Records a received bundle. This should be called after processing the
-	 * bundle's contents, and may result in outstanding messages becoming
-	 * eligible for retransmission.
-	 * <p>
-	 * Locking: contacts read, messages read, messageStatuses write.
-	 */
-	Set<BatchId> addReceivedBundle(T txn, ContactId c, BundleId b) throws DbException;
-
 	/**
 	 * Subscribes to the given group.
 	 * <p>
@@ -167,6 +153,14 @@ interface Database<T> {
 	 */
 	GroupId getGroup(T txn, MessageId m) throws DbException;
 
+	/**
+	 * Returns the IDs of any batches sent to the given contact that should now
+	 * be considered lost.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses read.
+	 */
+	Set<BatchId> getLostBatches(T txn, ContactId c) throws DbException;
+
 	/**
 	 * Returns the message identified by the given ID.
 	 * <p>

components/net/sf/briar/db/H2Database.java

@@ -30,7 +30,7 @@ class H2Database extends JdbcDatabase {
 	@Inject
 	H2Database(File dir, MessageFactory messageFactory,
 			@DatabasePassword Password password, long maxSize) {
-		super(messageFactory, "BINARY(32)");
+		super(messageFactory, "BINARY(32)", "BIGINT");
 		home = new File(dir, "db");
 		this.password = password;
 		url = "jdbc:h2:split:" + home.getPath()

components/net/sf/briar/db/JdbcDatabase.java

@@ -9,7 +9,6 @@ import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
@@ -26,7 +25,6 @@ import net.sf.briar.api.db.DbException;
 import net.sf.briar.api.db.Status;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Message;
 import net.sf.briar.api.protocol.MessageFactory;
@@ -73,7 +71,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 	private static final String CREATE_CONTACTS =
 		"CREATE TABLE contacts"
 		+ " (contactId INT NOT NULL,"
-		+ " lastBundleReceived XXXX NOT NULL,"
 		+ " PRIMARY KEY (contactId))";
 
 	private static final String CREATE_BATCHES_TO_ACK =
@@ -96,7 +93,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 		"CREATE TABLE outstandingBatches"
 		+ " (batchId XXXX NOT NULL,"
 		+ " contactId INT NOT NULL,"
-		+ " lastBundleReceived XXXX NOT NULL,"
+		+ " timestamp YYYY NOT NULL,"
+		+ " passover INT NOT NULL,"
 		+ " PRIMARY KEY (batchId),"
 		+ " FOREIGN KEY (contactId) REFERENCES contacts (contactId)"
 		+ " ON DELETE CASCADE)";
@@ -124,15 +122,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		+ " rating SMALLINT NOT NULL,"
 		+ " PRIMARY KEY (authorId))";
 
-	private static final String CREATE_RECEIVED_BUNDLES =
-		"CREATE TABLE receivedBundles"
-		+ " (bundleId XXXX NOT NULL,"
-		+ " contactId INT NOT NULL,"
-		+ " timestamp BIGINT NOT NULL,"
-		+ " PRIMARY KEY (bundleId, contactId),"
-		+ " FOREIGN KEY (contactId) REFERENCES contacts (contactId)"
-		+ " ON DELETE CASCADE)";
-
 	private static final String CREATE_STATUSES =
 		"CREATE TABLE statuses"
 		+ " (messageId XXXX NOT NULL,"
@@ -169,7 +158,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 		Logger.getLogger(JdbcDatabase.class.getName());
 
 	private final MessageFactory messageFactory;
-	private final String hashType;
+	// Different database libraries use different names for certain types
+	private final String hashType, bigIntType;
 	private final LinkedList<Connection> connections =
 		new LinkedList<Connection>(); // Locking: self
 
@@ -178,9 +168,11 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	protected abstract Connection createConnection() throws SQLException;
 
-	JdbcDatabase(MessageFactory messageFactory, String hashType) {
+	JdbcDatabase(MessageFactory messageFactory, String hashType,
+			String bigIntType) {
 		this.messageFactory = messageFactory;
 		this.hashType = hashType;
+		this.bigIntType = bigIntType;
 	}
 
 	protected void open(boolean resume, File dir, String driverClass)
@@ -219,47 +211,44 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s = txn.createStatement();
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating localSubscriptions table");
-			s.executeUpdate(insertHashType(CREATE_LOCAL_SUBSCRIPTIONS));
+			s.executeUpdate(insertTypeNames(CREATE_LOCAL_SUBSCRIPTIONS));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating messages table");
-			s.executeUpdate(insertHashType(CREATE_MESSAGES));
+			s.executeUpdate(insertTypeNames(CREATE_MESSAGES));
 			s.executeUpdate(INDEX_MESSAGES_BY_PARENT);
 			s.executeUpdate(INDEX_MESSAGES_BY_AUTHOR);
 			s.executeUpdate(INDEX_MESSAGES_BY_TIMESTAMP);
 			s.executeUpdate(INDEX_MESSAGES_BY_SENDABILITY);
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating contacts table");
-			s.executeUpdate(insertHashType(CREATE_CONTACTS));
+			s.executeUpdate(insertTypeNames(CREATE_CONTACTS));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating batchesToAck table");
-			s.executeUpdate(insertHashType(CREATE_BATCHES_TO_ACK));
+			s.executeUpdate(insertTypeNames(CREATE_BATCHES_TO_ACK));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating contactSubscriptions table");
-			s.executeUpdate(insertHashType(CREATE_CONTACT_SUBSCRIPTIONS));
+			s.executeUpdate(insertTypeNames(CREATE_CONTACT_SUBSCRIPTIONS));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating outstandingBatches table");
-			s.executeUpdate(insertHashType(CREATE_OUTSTANDING_BATCHES));
+			s.executeUpdate(insertTypeNames(CREATE_OUTSTANDING_BATCHES));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating outstandingMessages table");
-			s.executeUpdate(insertHashType(CREATE_OUTSTANDING_MESSAGES));
+			s.executeUpdate(insertTypeNames(CREATE_OUTSTANDING_MESSAGES));
 			s.executeUpdate(INDEX_OUTSTANDING_MESSAGES_BY_BATCH);
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating ratings table");
-			s.executeUpdate(insertHashType(CREATE_RATINGS));
+			s.executeUpdate(insertTypeNames(CREATE_RATINGS));
-			if(LOG.isLoggable(Level.FINE))
-				LOG.fine("Creating receivedBundles table");
-			s.executeUpdate(insertHashType(CREATE_RECEIVED_BUNDLES));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating statuses table");
-			s.executeUpdate(insertHashType(CREATE_STATUSES));
+			s.executeUpdate(insertTypeNames(CREATE_STATUSES));
 			s.executeUpdate(INDEX_STATUSES_BY_MESSAGE);
 			s.executeUpdate(INDEX_STATUSES_BY_CONTACT);
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating contact transports table");
-			s.executeUpdate(insertHashType(CREATE_CONTACT_TRANSPORTS));
+			s.executeUpdate(insertTypeNames(CREATE_CONTACT_TRANSPORTS));
 			if(LOG.isLoggable(Level.FINE))
 				LOG.fine("Creating local transports table");
-			s.executeUpdate(insertHashType(CREATE_LOCAL_TRANSPORTS));
+			s.executeUpdate(insertTypeNames(CREATE_LOCAL_TRANSPORTS));
 			s.close();
 		} catch(SQLException e) {
 			tryToClose(s);
@@ -268,9 +257,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	// FIXME: Get rid of this if we're definitely not using Derby
+	private String insertTypeNames(String s) {
-	private String insertHashType(String s) {
+		return s.replaceAll("XXXX", hashType).replaceAll("YYYY", bigIntType);
-		return s.replaceAll("XXXX", hashType);
 	}
 
 	private void tryToClose(Connection c) {
@@ -371,8 +359,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 	throws DbException {
 		PreparedStatement ps = null;
 		try {
-			String sql = "INSERT INTO batchesToAck"
+			String sql = "INSERT INTO batchesToAck (batchId, contactId)"
-				+ " (batchId, contactId)"
 				+ " VALUES (?, ?)";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, b.getBytes());
@@ -405,30 +392,15 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs.close();
 			ps.close();
 			// Create a new contact row
-			sql = "INSERT INTO contacts"
+			sql = "INSERT INTO contacts (contactId) VALUES (?)";
-				+ " (contactId, lastBundleReceived)"
-				+ " VALUES (?, ?)";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, c.getInt());
-			ps.setBytes(2, BundleId.NONE.getBytes());
 			int rowsAffected = ps.executeUpdate();
 			assert rowsAffected == 1;
 			ps.close();
-			// Create a dummy received bundle row for BundleId.NONE
-			sql = "INSERT INTO receivedBundles"
-				+ " (bundleId, contactId, timestamp)"
-				+ " VALUES (?, ?, ?)";
-			ps = txn.prepareStatement(sql);
-			ps.setBytes(1, BundleId.NONE.getBytes());
-			ps.setInt(2, c.getInt());
-			ps.setLong(3, System.currentTimeMillis());
-			rowsAffected = ps.executeUpdate();
-			assert rowsAffected == 1;
-			ps.close();
 			// Store the contact's transport details
 			if(transports != null) {
-				sql = "INSERT INTO contactTransports"
+				sql = "INSERT INTO contactTransports (contactId, key, value)"
-					+ " (contactId, key, value)"
 					+ " VALUES (?, ?, ?)";
 				ps = txn.prepareStatement(sql);
 				ps.setInt(1, c.getInt());
@@ -485,27 +457,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
-			// Find the ID of the last bundle received from c
-			String sql = "SELECT lastBundleReceived FROM contacts"
-				+ " WHERE contactId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			rs = ps.executeQuery();
-			boolean found = rs.next();
-			assert found;
-			byte[] lastBundleReceived = rs.getBytes(1);
-			boolean more = rs.next();
-			assert !more;
-			rs.close();
-			ps.close();
 			// Create an outstanding batch row
-			sql = "INSERT INTO outstandingBatches"
+			String sql = "INSERT INTO outstandingBatches"
-				+ " (batchId, contactId, lastBundleReceived)"
+				+ " (batchId, contactId, timestamp, passover)"
-				+ " VALUES (?, ?, ?)";
+				+ " VALUES (?, ?, ?, ZERO())";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, b.getBytes());
 			ps.setInt(2, c.getInt());
-			ps.setBytes(3, lastBundleReceived);
+			ps.setLong(3, System.currentTimeMillis());
 			int rowsAffected = ps.executeUpdate();
 			assert rowsAffected == 1;
 			ps.close();
@@ -551,98 +510,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	public Set<BatchId> addReceivedBundle(Connection txn, ContactId c,
-			BundleId b) throws DbException {
-		PreparedStatement ps = null;
-		ResultSet rs = null;
-		try {
-			// Update the ID of the last bundle received from c
-			String sql = "UPDATE contacts SET lastBundleReceived = ?"
-				+ " WHERE contactId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setBytes(1, b.getBytes());
-			ps.setInt(2, c.getInt());
-			int rowsAffected = ps.executeUpdate();
-			assert rowsAffected == 1;
-			ps.close();
-			// Count the received bundle records for c and find the oldest
-			sql = "SELECT bundleId, timestamp FROM receivedBundles"
-				+ " WHERE contactId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			rs = ps.executeQuery();
-			int received = 0;
-			long oldestTimestamp = Long.MAX_VALUE;
-			byte[] oldestBundle = null;
-			while(rs.next()) {
-				received++;
-				byte[] bundle = rs.getBytes(1);
-				long timestamp = rs.getLong(2);
-				if(timestamp < oldestTimestamp) {
-					oldestTimestamp = timestamp;
-					oldestBundle = bundle;
-				}
-			}
-			rs.close();
-			ps.close();
-			Set<BatchId> lost;
-			if(received == RETRANSMIT_THRESHOLD) {
-				// Expire batches related to the oldest received bundle
-				assert oldestBundle != null;
-				lost = findLostBatches(txn, c, oldestBundle);
-				sql = "DELETE FROM receivedBundles WHERE bundleId = ?";
-				ps = txn.prepareStatement(sql);
-				ps.setBytes(1, oldestBundle);
-				rowsAffected = ps.executeUpdate();
-				assert rowsAffected == 1;
-				ps.close();
-			} else {
-				lost = Collections.emptySet();
-			}
-			// Record the new received bundle
-			sql = "INSERT INTO receivedBundles"
-				+ " (bundleId, contactId, timestamp)"
-				+ " VALUES (?, ?, ?)";
-			ps = txn.prepareStatement(sql);
-			ps.setBytes(1, b.getBytes());
-			ps.setInt(2, c.getInt());
-			ps.setLong(3, System.currentTimeMillis());
-			rowsAffected = ps.executeUpdate();
-			assert rowsAffected == 1;
-			ps.close();
-			return lost;
-		} catch(SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
-			tryToClose(txn);
-			throw new DbException(e);
-		}
-	}
-
-	private Set<BatchId> findLostBatches(Connection txn, ContactId c,
-			byte[] lastBundleReceived) throws DbException {
-		PreparedStatement ps = null;
-		ResultSet rs = null;
-		try {
-			String sql = "SELECT batchId FROM outstandingBatches"
-				+ " WHERE contactId = ? AND lastBundleReceived = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			ps.setBytes(2, lastBundleReceived);
-			rs = ps.executeQuery();
-			Set<BatchId> lost = new HashSet<BatchId>();
-			while(rs.next()) lost.add(new BatchId(rs.getBytes(1)));
-			rs.close();
-			ps.close();
-			return lost;
-		} catch(SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
-			tryToClose(txn);
-			throw new DbException(e);
-		}
-	}
-
 	public void addSubscription(Connection txn, GroupId g) throws DbException {
 		PreparedStatement ps = null;
 		try {
@@ -829,6 +696,30 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public Set<BatchId> getLostBatches(Connection txn, ContactId c)
+	throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT batchId FROM outstandingBatches"
+				+ " WHERE contactId = ? AND passover >= ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, RETRANSMIT_THRESHOLD);
+			rs = ps.executeQuery();
+			Set<BatchId> ids = new HashSet<BatchId>();
+			while(rs.next()) ids.add(new BatchId(rs.getBytes(1)));
+			rs.close();
+			ps.close();
+			return ids;
+		} catch(SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			tryToClose(txn);
+			throw new DbException(e);
+		}
+	}
+
 	public Message getMessage(Connection txn, MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1158,6 +1049,38 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	public void removeAckedBatch(Connection txn, ContactId c, BatchId b)
 	throws DbException {
+		// Increment the passover count of all older outstanding batches
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT timestamp FROM outstandingBatches"
+				+ " WHERE contactId = ? AND batchId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setBytes(2, b.getBytes());
+			rs = ps.executeQuery();
+			boolean found = rs.next();
+			assert found;
+			long timestamp = rs.getLong(1);
+			boolean more = rs.next();
+			assert !more;
+			rs.close();
+			ps.close();
+			sql = "UPDATE outstandingBatches SET passover = passover + ?"
+				+ " WHERE contactId = ? AND timestamp < ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, 1);
+			ps.setInt(2, c.getInt());
+			ps.setLong(3, timestamp);
+			int rowsAffected = ps.executeUpdate();
+			assert rowsAffected >= 0;
+			ps.close();
+		} catch(SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			tryToClose(txn);
+			throw new DbException(e);
+		}
 		removeBatch(txn, c, b, Status.SEEN);
 	}
 

components/net/sf/briar/db/ReadWriteLockDatabaseComponent.java

@@ -19,7 +19,6 @@ import net.sf.briar.api.db.NoSuchContactException;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.Batch;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.BundleReader;
 import net.sf.briar.api.protocol.BundleWriter;
 import net.sf.briar.api.protocol.GroupId;
@@ -525,7 +524,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine("Received " + batches + " batches");
 		b.finish();
-		retransmitLostBatches(c, h.getId());
+		findLostBatches(c);
 		System.gc();
 	}
 
@@ -573,8 +572,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		}
 	}
 
-	private void retransmitLostBatches(ContactId c, BundleId b)
+	private void findLostBatches(ContactId c) throws DbException {
-	throws DbException {
 		// Find any lost batches that need to be retransmitted
 		Set<BatchId> lost;
 		contactLock.readLock().lock();
@@ -586,7 +584,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				try {
 					Txn txn = db.startTransaction();
 					try {
-						lost = db.addReceivedBundle(txn, c, b);
+						lost = db.getLostBatches(txn, c);
 						db.commitTransaction(txn);
 					} catch(DbException e) {
 						db.abortTransaction(txn);

components/net/sf/briar/db/SynchronizedDatabaseComponent.java

@@ -19,7 +19,6 @@ import net.sf.briar.api.db.NoSuchContactException;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.Batch;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.BundleReader;
 import net.sf.briar.api.protocol.BundleWriter;
 import net.sf.briar.api.protocol.GroupId;
@@ -396,7 +395,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine("Received " + batches + " batches");
 		b.finish();
-		retransmitLostBatches(c, h.getId());
+		findLostBatches(c);
 		System.gc();
 	}
 
@@ -432,7 +431,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		}
 	}
 
-	private void retransmitLostBatches(ContactId c, BundleId b)
+	private void findLostBatches(ContactId c)
 	throws DbException {
 		// Find any lost batches that need to be retransmitted
 		Set<BatchId> lost;
@@ -442,7 +441,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				synchronized(messageStatusLock) {
 					Txn txn = db.startTransaction();
 					try {
-						lost = db.addReceivedBundle(txn, c, b);
+						lost = db.getLostBatches(txn, c);
 						db.commitTransaction(txn);
 					} catch(DbException e) {
 						db.abortTransaction(txn);

components/net/sf/briar/protocol/BundleReaderImpl.java

@@ -15,7 +15,6 @@ import java.util.Set;
 
 import net.sf.briar.api.protocol.Batch;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.BundleReader;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Header;
@@ -66,7 +65,6 @@ class BundleReaderImpl implements BundleReader {
 		signature.initVerify(publicKey);
 		messageDigest.reset();
 		// Read the signed data
-		in.setDigesting(true);
 		in.setSigning(true);
 		r.setReadLimit(Header.MAX_SIZE);
 		Set<BatchId> acks = new HashSet<BatchId>();
@@ -86,11 +84,9 @@ class BundleReaderImpl implements BundleReader {
 		in.setSigning(false);
 		// Read and verify the signature
 		byte[] sig = r.readRaw();
-		in.setDigesting(false);
 		if(!signature.verify(sig)) throw new SignatureException();
 		// Build and return the header
-		BundleId id = new BundleId(messageDigest.digest());
+		return headerFactory.createHeader(acks, subs, transports);
-		return headerFactory.createHeader(id, acks, subs, transports);
 	}
 
 	public Batch getNextBatch() throws IOException, GeneralSecurityException {

components/net/sf/briar/protocol/BundleWriterImpl.java

@@ -2,7 +2,6 @@ package net.sf.briar.protocol;
 
 import java.io.IOException;
 import java.io.OutputStream;
-import java.security.DigestOutputStream;
 import java.security.GeneralSecurityException;
 import java.security.MessageDigest;
 import java.security.PrivateKey;
@@ -10,7 +9,6 @@ import java.security.Signature;
 import java.util.Map;
 
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.BundleWriter;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Message;
@@ -22,7 +20,7 @@ class BundleWriterImpl implements BundleWriter {
 
 	private static enum State { START, FIRST_BATCH, MORE_BATCHES, END };
 
-	private final SigningOutputStream out;
+	private final SigningDigestingOutputStream out;
 	private final Writer w;
 	private final PrivateKey privateKey;
 	private final Signature signature;
@@ -33,8 +31,8 @@ class BundleWriterImpl implements BundleWriter {
 	BundleWriterImpl(OutputStream out, WriterFactory writerFactory,
 			PrivateKey privateKey, Signature signature,
 			MessageDigest messageDigest, long capacity) {
-		OutputStream out1 = new DigestOutputStream(out, messageDigest);
+		this.out =
-		this.out = new SigningOutputStream(out1, signature);
+			new SigningDigestingOutputStream(out, signature, messageDigest);
 		w = writerFactory.createWriter(this.out);
 		this.privateKey = privateKey;
 		this.signature = signature;
@@ -46,13 +44,12 @@ class BundleWriterImpl implements BundleWriter {
 		return capacity - w.getRawBytesWritten();
 	}
 
-	public BundleId addHeader(Iterable<BatchId> acks, Iterable<GroupId> subs,
+	public void addHeader(Iterable<BatchId> acks, Iterable<GroupId> subs,
 			Map<String, String> transports) throws IOException,
 			GeneralSecurityException {
 		if(state != State.START) throw new IllegalStateException();
 		// Initialise the output stream
 		signature.initSign(privateKey);
-		messageDigest.reset();
 		// Write the data to be signed
 		out.setSigning(true);
 		w.writeListStart();
@@ -66,9 +63,8 @@ class BundleWriterImpl implements BundleWriter {
 		// Create and write the signature
 		byte[] sig = signature.sign();
 		w.writeRaw(sig);
-		// Calculate and return the ID
+		// Expect a (possibly empty) list of batches
 		state = State.FIRST_BATCH;
-		return new BundleId(messageDigest.digest());
 	}
 
 	public BatchId addBatch(Iterable<Message> messages) throws IOException,
@@ -82,6 +78,7 @@ class BundleWriterImpl implements BundleWriter {
 		signature.initSign(privateKey);
 		messageDigest.reset();
 		// Write the data to be signed
+		out.setDigesting(true);
 		out.setSigning(true);
 		w.writeListStart();
 		for(Message m : messages) w.writeRaw(m);
@@ -90,6 +87,7 @@ class BundleWriterImpl implements BundleWriter {
 		// Create and write the signature
 		byte[] sig = signature.sign();
 		w.writeRaw(sig);
+		out.setDigesting(false);
 		// Calculate and return the ID
 		return new BatchId(messageDigest.digest());
 	}

components/net/sf/briar/protocol/HeaderFactory.java

@@ -4,12 +4,11 @@ import java.util.Map;
 import java.util.Set;
 
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Header;
 
 interface HeaderFactory {
 
-	Header createHeader(BundleId id, Set<BatchId> acks, Set<GroupId> subs,
+	Header createHeader(Set<BatchId> acks, Set<GroupId> subs,
 			Map<String, String> transports);
 }

components/net/sf/briar/protocol/HeaderFactoryImpl.java

@@ -4,14 +4,13 @@ import java.util.Map;
 import java.util.Set;
 
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Header;
 
 class HeaderFactoryImpl implements HeaderFactory {
 
-	public Header createHeader(BundleId id, Set<BatchId> acks,
+	public Header createHeader(Set<BatchId> acks, Set<GroupId> subs,
-			Set<GroupId> subs, Map<String, String> transports) {
+			Map<String, String> transports) {
-		return new HeaderImpl(id, acks, subs, transports);
+		return new HeaderImpl(acks, subs, transports);
 	}
 }

components/net/sf/briar/protocol/HeaderImpl.java

@@ -4,30 +4,23 @@ import java.util.Map;
 import java.util.Set;
 
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Header;
 
 /** A simple in-memory implementation of a header. */
 class HeaderImpl implements Header {
 
-	private final BundleId id;
 	private final Set<BatchId> acks;
 	private final Set<GroupId> subs;
 	private final Map<String, String> transports;
 
-	HeaderImpl(BundleId id, Set<BatchId> acks, Set<GroupId> subs,
+	HeaderImpl(Set<BatchId> acks, Set<GroupId> subs,
 			Map<String, String> transports) {
-		this.id = id;
 		this.acks = acks;
 		this.subs = subs;
 		this.transports = transports;
 	}
 
-	public BundleId getId() {
-		return id;
-	}
-
 	public Set<BatchId> getAcks() {
 		return acks;
 	}

components/net/sf/briar/protocol/SigningDigestingOutputStream.java

@@ -3,24 +3,35 @@ package net.sf.briar.protocol;
 import java.io.FilterOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.security.MessageDigest;
 import java.security.Signature;
 import java.security.SignatureException;
 
-/** An output stream that passes its output through a signature. */
+/**
-class SigningOutputStream extends FilterOutputStream {
+ * An output stream that passes its output through a signature and a message
+ * digest.
+ */
+class SigningDigestingOutputStream extends FilterOutputStream {
 
 	private final Signature signature;
-	private boolean signing = false;
+	private final MessageDigest messageDigest;
+	private boolean signing = false, digesting = false;
 
-	public SigningOutputStream(OutputStream out, Signature signature) {
+	public SigningDigestingOutputStream(OutputStream out, Signature signature,
+			MessageDigest messageDigest) {
 		super(out);
 		this.signature = signature;
+		this.messageDigest = messageDigest;
 	}
 
 	void setSigning(boolean signing) {
 		this.signing = signing;
 	}
 
+	void setDigesting(boolean digesting) {
+		this.digesting = digesting;
+	}
+
 	@Override
 	public void write(byte[] b) throws IOException {
 		write(b, 0, b.length);
@@ -36,6 +47,7 @@ class SigningOutputStream extends FilterOutputStream {
 				throw new IOException(e);
 			}
 		}
+		if(digesting) messageDigest.update(b, off, len);
 	}
 
 	@Override
@@ -48,5 +60,6 @@ class SigningOutputStream extends FilterOutputStream {
 				throw new IOException(e);
 			}
 		}
+		if(digesting) messageDigest.update((byte) b);
 	}
 }

test/net/sf/briar/db/DatabaseComponentTest.java

@@ -15,7 +15,6 @@ import net.sf.briar.api.db.Status;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.Batch;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.BundleReader;
 import net.sf.briar.api.protocol.BundleWriter;
 import net.sf.briar.api.protocol.GroupId;
@@ -33,7 +32,6 @@ public abstract class DatabaseComponentTest extends TestCase {
 	protected final Object txn = new Object();
 	protected final AuthorId authorId;
 	protected final BatchId batchId;
-	protected final BundleId bundleId;
 	protected final ContactId contactId;
 	protected final GroupId groupId;
 	protected final MessageId messageId, parentId;
@@ -51,7 +49,6 @@ public abstract class DatabaseComponentTest extends TestCase {
 		super();
 		authorId = new AuthorId(TestUtils.getRandomId());
 		batchId = new BatchId(TestUtils.getRandomId());
-		bundleId = new BundleId(TestUtils.getRandomId());
 		contactId = new ContactId(123);
 		groupId = new GroupId(TestUtils.getRandomId());
 		messageId = new MessageId(TestUtils.getRandomId());
@@ -478,7 +475,6 @@ public abstract class DatabaseComponentTest extends TestCase {
 			will(returnValue(transports));
 			// Build the header
 			oneOf(bundleWriter).addHeader(acks, subs, transports);
-			will(returnValue(bundleId));
 			// Add a batch to the bundle
 			oneOf(bundleWriter).getRemainingCapacity();
 			will(returnValue(1024L * 1024L - headerSize));
@@ -579,9 +575,7 @@ public abstract class DatabaseComponentTest extends TestCase {
 			will(returnValue(null));
 			oneOf(bundleReader).finish();
 			// Lost batches
-			oneOf(header).getId();
+			oneOf(database).getLostBatches(txn, contactId);
-			will(returnValue(bundleId));
-			oneOf(database).addReceivedBundle(txn, contactId, bundleId);
 			will(returnValue(Collections.singleton(batchId)));
 			oneOf(database).removeLostBatch(txn, contactId, batchId);
 		}});

test/net/sf/briar/db/H2DatabaseTest.java

@@ -21,7 +21,6 @@ import net.sf.briar.api.db.DbException;
 import net.sf.briar.api.db.Status;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.BatchId;
-import net.sf.briar.api.protocol.BundleId;
 import net.sf.briar.api.protocol.GroupId;
 import net.sf.briar.api.protocol.Message;
 import net.sf.briar.api.protocol.MessageFactory;
@@ -489,13 +488,10 @@ public class H2DatabaseTest extends TestCase {
 
 	@Test
 	public void testRetransmission() throws DbException {
-		BundleId bundleId = new BundleId(TestUtils.getRandomId());
+		BatchId[] ids = new BatchId[Database.RETRANSMIT_THRESHOLD + 5];
-		BundleId bundleId1 = new BundleId(TestUtils.getRandomId());
+		for(int i = 0; i < ids.length; i++) {
-		BundleId bundleId2 = new BundleId(TestUtils.getRandomId());
+			ids[i] = new BatchId(TestUtils.getRandomId());
-		BundleId bundleId3 = new BundleId(TestUtils.getRandomId());
+		}
-		BundleId bundleId4 = new BundleId(TestUtils.getRandomId());
-		BatchId batchId1 = new BatchId(TestUtils.getRandomId());
-		BatchId batchId2 = new BatchId(TestUtils.getRandomId());
 		Set<MessageId> empty = Collections.emptySet();
 		Mockery context = new Mockery();
 		MessageFactory messageFactory = context.mock(MessageFactory.class);
@@ -504,30 +500,62 @@ public class H2DatabaseTest extends TestCase {
 		// Add a contact
 		Connection txn = db.startTransaction();
 		assertEquals(contactId, db.addContact(txn, null));
-		// Add an oustanding batch (associated with BundleId.NONE)
+		// Add some outstanding batches, a few ms apart
-		db.addOutstandingBatch(txn, contactId, batchId, empty);
+		for(int i = 0; i < ids.length; i++) {
-		// Receive a bundle
+			db.addOutstandingBatch(txn, contactId, ids[i], empty);
-		Set<BatchId> lost = db.addReceivedBundle(txn, contactId, bundleId);
+			try {
-		assertTrue(lost.isEmpty());
+				Thread.sleep(5);
-		// Add a couple more outstanding batches (associated with bundleId)
+			} catch(InterruptedException ignored) {}
-		db.addOutstandingBatch(txn, contactId, batchId1, empty);
+		}
-		db.addOutstandingBatch(txn, contactId, batchId2, empty);
+		// The contact acks the batches in reverse order. The first
-		// Receive another bundle
+		// RETRANSMIT_THRESHOLD - 1 acks should not trigger any retransmissions
-		lost = db.addReceivedBundle(txn, contactId, bundleId1);
+		for(int i = 0; i < Database.RETRANSMIT_THRESHOLD - 1; i++) {
-		assertTrue(lost.isEmpty());
+			db.removeAckedBatch(txn, contactId, ids[ids.length - i - 1]);
-		// The contact acks one of the batches - it should not be retransmitted
+			Set<BatchId> lost = db.getLostBatches(txn, contactId);
-		db.removeAckedBatch(txn, contactId, batchId1);
+			assertEquals(Collections.emptySet(), lost);
-		// Receive another bundle - batchId should now be considered lost
+		}
-		lost = db.addReceivedBundle(txn, contactId, bundleId2);
+		// The next ack should trigger the retransmission of the remaining
-		assertEquals(1, lost.size());
+		// five outstanding batches
-		assertTrue(lost.contains(batchId));
+		int index = ids.length - Database.RETRANSMIT_THRESHOLD;
-		// Receive another bundle - batchId2 should now be considered lost
+		db.removeAckedBatch(txn, contactId, ids[index]);
-		lost = db.addReceivedBundle(txn, contactId, bundleId3);
+		Set<BatchId> lost = db.getLostBatches(txn, contactId);
-		assertEquals(1, lost.size());
+		for(int i = 0; i < index; i++) {
-		assertTrue(lost.contains(batchId2));
+			assertTrue(lost.contains(ids[i]));
-		// Receive another bundle - no further losses
+		}
-		lost = db.addReceivedBundle(txn, contactId, bundleId4);
+		db.commitTransaction(txn);
-		assertTrue(lost.isEmpty());
+
+		db.close();
+		context.assertIsSatisfied();
+	}
+
+	@Test
+	public void testNoRetransmission() throws DbException {
+		BatchId[] ids = new BatchId[Database.RETRANSMIT_THRESHOLD * 2];
+		for(int i = 0; i < ids.length; i++) {
+			ids[i] = new BatchId(TestUtils.getRandomId());
+		}
+		Set<MessageId> empty = Collections.emptySet();
+		Mockery context = new Mockery();
+		MessageFactory messageFactory = context.mock(MessageFactory.class);
+		Database<Connection> db = open(false, messageFactory);
+
+		// Add a contact
+		Connection txn = db.startTransaction();
+		assertEquals(contactId, db.addContact(txn, null));
+		// Add some outstanding batches, a few ms apart
+		for(int i = 0; i < ids.length; i++) {
+			db.addOutstandingBatch(txn, contactId, ids[i], empty);
+			try {
+				Thread.sleep(5);
+			} catch(InterruptedException ignored) {}
+		}
+		// The contact acks the batches in the order they were sent - nothing
+		// should be retransmitted
+		for(int i = 0; i < ids.length; i++) {
+			db.removeAckedBatch(txn, contactId, ids[i]);
+			Set<BatchId> lost = db.getLostBatches(txn, contactId);
+			assertEquals(Collections.emptySet(), lost);
+		}
 		db.commitTransaction(txn);
 
 		db.close();

test/net/sf/briar/protocol/SigningStreamTest.java

@@ -2,7 +2,6 @@ package net.sf.briar.protocol;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.security.DigestOutputStream;
 import java.security.KeyPair;
 import java.security.KeyPairGenerator;
 import java.security.MessageDigest;
@@ -39,7 +38,8 @@ public class SigningStreamTest extends TestCase {
 		random.nextBytes(input);
 
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
-		SigningOutputStream signOut = new SigningOutputStream(out, sig);
+		SigningDigestingOutputStream signOut =
+			new SigningDigestingOutputStream(out, sig, dig);
 		sig.initSign(keyPair.getPrivate());
 
 		signOut.setSigning(true);
@@ -80,7 +80,8 @@ public class SigningStreamTest extends TestCase {
 		random.nextBytes(input);
 
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
-		SigningOutputStream signOut = new SigningOutputStream(out, sig);
+		SigningDigestingOutputStream signOut =
+			new SigningDigestingOutputStream(out, sig, dig);
 		sig.initSign(keyPair.getPrivate());
 
 		// Sign bytes 0-499, skip bytes 500-749, sign bytes 750-999
@@ -121,16 +122,17 @@ public class SigningStreamTest extends TestCase {
 		random.nextBytes(input);
 
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
-		DigestOutputStream digOut = new DigestOutputStream(out, dig);
+		SigningDigestingOutputStream signOut =
+			new SigningDigestingOutputStream(out, sig, dig);
 		dig.reset();
 
 		// Digest bytes 0-499, skip bytes 500-749, digest bytes 750-999
-		digOut.on(true);
+		signOut.setDigesting(true);
-		digOut.write(input, 0, 500);
+		signOut.write(input, 0, 500);
-		digOut.on(false);
+		signOut.setDigesting(false);
-		digOut.write(input, 500, 250);
+		signOut.write(input, 500, 250);
-		digOut.on(true);
+		signOut.setDigesting(true);
-		digOut.write(input, 750, 250);
+		signOut.write(input, 750, 250);
 
 		byte[] hash = dig.digest();