bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -25,6 +25,7 @@ import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 
 import javax.annotation.Nullable;
@@ -150,6 +151,8 @@ public interface DatabaseComponent {
 	boolean containsLocalAuthor(Transaction txn, AuthorId local)
 			throws DbException;
 
+	int countFakes(Transaction txn, List<byte[]> ids) throws DbException;
+
 	/**
 	 * Deletes the message with the given ID. Unlike
 	 * {@link #removeMessage(Transaction, MessageId)}, the message ID,

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

@@ -28,6 +28,7 @@ import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 
 import javax.annotation.Nullable;
@@ -188,6 +189,8 @@ interface Database<T> {
 	boolean containsVisibleMessage(T txn, ContactId c, MessageId m)
 			throws DbException;
 
+	int countFakes(T txn, List<byte[]> ids) throws DbException;
+
 	/**
 	 * Returns the number of messages offered by the given contact.
 	 * <p/>

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

@@ -313,6 +313,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.containsLocalAuthor(txn, local);
 	}
 
+	@Override
+	public int countFakes(Transaction transaction, List<byte[]> ids)
+		throws DbException {
+		T txn = unbox(transaction);
+		return db.countFakes(txn, ids);
+	}
+
 	@Override
 	public void deleteMessage(Transaction transaction, MessageId m)
 			throws DbException {

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

 package org.briarproject.bramble.db;
 
+import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
@@ -47,6 +48,7 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.Lock;
@@ -92,6 +94,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 	private static final int OFFSET_CURR = 0;
 	private static final int OFFSET_NEXT = 1;
 
+	private static final int NUM_FAKES = 32 * 1024;
+
 	private static final String CREATE_SETTINGS =
 			"CREATE TABLE settings"
 					+ " (namespace _STRING NOT NULL,"
@@ -285,6 +289,20 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " REFERENCES contacts (contactId)"
 					+ " ON DELETE CASCADE)";
 
+	// In H2 the MEMORY keyword creates a persistent table with in-memory
+	// indexes, which must be dropped and recreated when reopening the database.
+	// In HyperSQL it creates a persistent table that's entirely cached in
+	// memory, which is the default. Dropping and recreating indexes is
+	// unnecessary.
+	private static final String CREATE_FAKES =
+			"CREATE MEMORY TABLE fakes (fakeId _HASH NOT NULL)";
+
+	private static final String DROP_INDEX_FAKES_BY_FAKE_ID =
+			"DROP INDEX IF EXISTS fakesByFakeId";
+
+	private static final String INDEX_FAKES_BY_FAKE_ID =
+			"CREATE INDEX fakesByFakeId ON fakes (fakeId)";
+
 	private static final String INDEX_CONTACTS_BY_AUTHOR_ID =
 			"CREATE INDEX IF NOT EXISTS contactsByAuthorId"
 					+ " ON contacts (authorId)";
@@ -376,6 +394,16 @@ abstract class JdbcDatabase implements Database<Connection> {
 			txn = startTransaction();
 			try {
 				storeLastCompacted(txn);
+				createInMemoryIndexes(txn);
+				commitTransaction(txn);
+			} catch (DbException e) {
+				abortTransaction(txn);
+				throw e;
+			}
+		} else {
+			txn = startTransaction();
+			try {
+				createInMemoryIndexes(txn);
 				commitTransaction(txn);
 			} catch (DbException e) {
 				abortTransaction(txn);
@@ -461,6 +489,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	private void createTables(Connection txn) throws DbException {
 		Statement s = null;
+		PreparedStatement ps = null;
 		try {
 			s = txn.createStatement();
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_SETTINGS));
@@ -477,9 +506,29 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_TRANSPORTS));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_OUTGOING_KEYS));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_INCOMING_KEYS));
+			s.executeUpdate(dbTypes.replaceTypes(CREATE_FAKES));
 			s.close();
+			Random random = new Random();
+			long start = now();
+			ps = txn.prepareStatement("INSERT INTO fakes (fakeId) VALUES (?)");
+			int inserted = 0;
+			while (inserted < NUM_FAKES) {
+				int batchSize = Math.min(1024, NUM_FAKES - inserted);
+				for (int i = 0; i < batchSize; i++) {
+					byte[] id = new byte[UniqueId.LENGTH];
+					random.nextBytes(id);
+					ps.setBytes(1, id);
+					ps.addBatch();
+				}
+				ps.executeBatch();
+				inserted += batchSize;
+			}
+			ps.close();
+			LOG.info("Inserting " + NUM_FAKES + " fakes took "
+					+ (now() - start) + " ms");
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -501,6 +550,21 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	private void createInMemoryIndexes(Connection txn) throws DbException {
+		Statement s = null;
+		try {
+			long start = now();
+			s = txn.createStatement();
+			s.executeUpdate(dbTypes.replaceTypes(DROP_INDEX_FAKES_BY_FAKE_ID));
+			s.executeUpdate(dbTypes.replaceTypes(INDEX_FAKES_BY_FAKE_ID));
+			s.close();
+			LOG.info("Indexing fakes took " + (now() - start) + " ms");
+		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public Connection startTransaction() throws DbException {
 		Connection txn;
@@ -1153,6 +1217,41 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public int countFakes(Connection txn, List<byte[]> ids)
+			throws DbException {
+		if (ids.isEmpty()) return 0;
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			long start = now();
+			StringBuilder sb = new StringBuilder();
+			sb.append("SELECT COUNT (fakeId) FROM fakes WHERE fakeId IN (?");
+			for (int i = 1; i < ids.size(); i++) {
+				sb.append(",?");
+			}
+			sb.append(')');
+			String sql = sb.toString();
+			ps = txn.prepareStatement(sql);
+			for (int i = 0; i < ids.size(); i++) {
+				ps.setBytes(i + 1, ids.get(i));
+			}
+			rs = ps.executeQuery();
+			if (!rs.next()) throw new DbException();
+			int count = rs.getInt(1);
+			if (rs.next()) throw new DbException();
+			rs.close();
+			ps.close();
+			LOG.info("Counting " + ids.size() + " fakes took "
+					+ (now() - start) + " ms, found " + count);
+			return count;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public int countOfferedMessages(Connection txn, ContactId c)
 			throws DbException {

bramble-core/src/test/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

@@ -131,6 +131,19 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertTrue(testDir.mkdirs());
 	}
 
+	@Test
+	public void testFakes() throws Exception {
+		List<byte[]> ids = new ArrayList<>(1024);
+		for (int i = 0; i < 1024; i++) {
+			ids.add(getRandomId());
+		}
+		Database<Connection> db = open(false);
+		Connection txn = db.startTransaction();
+		assertEquals(0, db.countFakes(txn, ids));
+		db.commitTransaction(txn);
+		db.close();
+	}
+
 	@Test
 	public void testPersistence() throws Exception {
 		// Store some records

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

@@ -12,6 +12,7 @@ import org.briarproject.bramble.api.contact.ContactExchangeTask;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
 import org.briarproject.bramble.api.crypto.PasswordStrengthEstimator;
+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.identity.IdentityManager;
@@ -82,6 +83,8 @@ public interface AndroidComponent
 	@DatabaseExecutor
 	Executor databaseExecutor();
 
+	DatabaseComponent databaseComponent();
+
 	MessageTracker messageTracker();
 
 	LifecycleManager lifecycleManager();

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerActivity.java

@@ -223,6 +223,7 @@ public class NavDrawerActivity extends BriarActivity implements
 
 	@Override
 	public boolean onNavigationItemSelected(@NonNull MenuItem item) {
+		controller.countFakes();
 		drawerLayout.closeDrawer(START);
 		clearBackStack();
 		if (item.getItemId() == R.id.nav_btn_lock) {

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerController.java

@@ -21,4 +21,5 @@ public interface NavDrawerController extends ActivityLifecycleController {
 	void shouldAskForDozeWhitelisting(Context ctx,
 			ResultHandler<Boolean> handler);
 
+	void countFakes();
 }

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerControllerImpl.java

@@ -3,6 +3,8 @@ package org.briarproject.briar.android.navdrawer;
 import android.app.Activity;
 import android.content.Context;
 
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.event.Event;
@@ -21,6 +23,9 @@ import org.briarproject.bramble.api.settings.SettingsManager;
 import org.briarproject.briar.android.controller.DbControllerImpl;
 import org.briarproject.briar.android.controller.handler.ResultHandler;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
@@ -49,6 +54,7 @@ public class NavDrawerControllerImpl extends DbControllerImpl
 	private static final String EXPIRY_DATE_WARNING = "expiryDateWarning";
 	private static final String EXPIRY_SHOW_UPDATE = "expiryShowUpdate";
 
+	private final DatabaseComponent db;
 	private final PluginManager pluginManager;
 	private final SettingsManager settingsManager;
 	private final EventBus eventBus;
@@ -57,9 +63,11 @@ public class NavDrawerControllerImpl extends DbControllerImpl
 
 	@Inject
 	NavDrawerControllerImpl(@DatabaseExecutor Executor dbExecutor,
-			LifecycleManager lifecycleManager, PluginManager pluginManager,
-			SettingsManager settingsManager, EventBus eventBus) {
+			DatabaseComponent db, LifecycleManager lifecycleManager,
+			PluginManager pluginManager, SettingsManager settingsManager,
+			EventBus eventBus) {
 		super(dbExecutor, lifecycleManager);
+		this.db = db;
 		this.pluginManager = pluginManager;
 		this.settingsManager = settingsManager;
 		this.eventBus = eventBus;
@@ -185,6 +193,25 @@ public class NavDrawerControllerImpl extends DbControllerImpl
 		});
 	}
 
+	@Override
+	public void countFakes() {
+		int numFakes = 1024;
+		Random random = new Random();
+		List<byte[]> ids = new ArrayList<>(numFakes);
+		for (int i = 0; i < numFakes; i++) {
+			byte[] id = new byte[UniqueId.LENGTH];
+			random.nextBytes(id);
+			ids.add(id);
+		}
+		runOnDbThread(() -> {
+			try {
+				db.transaction(true, txn -> db.countFakes(txn, ids));
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
 	@Override
 	public boolean isTransportRunning(TransportId transportId) {
 		Plugin plugin = pluginManager.getPlugin(transportId);