Use transactional database API in Bramble.

bramble-core/src/main/java/org/briarproject/bramble/client/ClientHelperImpl.java

@@ -82,13 +82,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void addLocalMessage(Message m, BdfDictionary metadata,
 			boolean shared) throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
-		try {
-			addLocalMessage(txn, m, metadata, shared);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> addLocalMessage(txn, m, metadata, shared));
 	}
 
 	@Override
@@ -113,15 +107,7 @@ class ClientHelperImpl implements ClientHelper {
 
 	@Override
 	public Message getMessage(MessageId m) throws DbException {
-		Message message;
-		Transaction txn = db.startTransaction(true);
-		try {
-			message = getMessage(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return message;
+		return db.transactionWithResult(true, txn -> getMessage(txn, m));
 	}
 
 	@Override
@@ -132,15 +118,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfList getMessageAsList(MessageId m) throws DbException,
 			FormatException {
-		BdfList list;
-		Transaction txn = db.startTransaction(true);
-		try {
-			list = getMessageAsList(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return list;
+		return db.transactionWithResult(true, txn -> getMessageAsList(txn, m));
 	}
 
 	@Override
@@ -152,15 +130,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfDictionary getGroupMetadataAsDictionary(GroupId g)
 			throws DbException, FormatException {
-		BdfDictionary dictionary;
-		Transaction txn = db.startTransaction(true);
-		try {
-			dictionary = getGroupMetadataAsDictionary(txn, g);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return dictionary;
+		return db.transactionWithResult(true, txn ->
+				getGroupMetadataAsDictionary(txn, g));
 	}
 
 	@Override
@@ -173,15 +144,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public BdfDictionary getMessageMetadataAsDictionary(MessageId m)
 			throws DbException, FormatException {
-		BdfDictionary dictionary;
-		Transaction txn = db.startTransaction(true);
-		try {
-			dictionary = getMessageMetadataAsDictionary(txn, m);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return dictionary;
+		return db.transactionWithResult(true,
+				txn -> getMessageMetadataAsDictionary(txn, m));
 	}
 
 	@Override
@@ -194,15 +158,8 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public Map<MessageId, BdfDictionary> getMessageMetadataAsDictionary(
 			GroupId g) throws DbException, FormatException {
-		Map<MessageId, BdfDictionary> map;
-		Transaction txn = db.startTransaction(true);
-		try {
-			map = getMessageMetadataAsDictionary(txn, g);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return map;
+		return db.transactionWithResult(true,
+				txn -> getMessageMetadataAsDictionary(txn, g));
 	}
 
 	@Override
@@ -219,15 +176,8 @@ class ClientHelperImpl implements ClientHelper {
 	public Map<MessageId, BdfDictionary> getMessageMetadataAsDictionary(
 			GroupId g, BdfDictionary query) throws DbException,
 			FormatException {
-		Map<MessageId, BdfDictionary> map;
-		Transaction txn = db.startTransaction(true);
-		try {
-			map = getMessageMetadataAsDictionary(txn, g, query);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return map;
+		return db.transactionWithResult(true,
+				txn -> getMessageMetadataAsDictionary(txn, g, query));
 	}
 
 	@Override
@@ -245,13 +195,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void mergeGroupMetadata(GroupId g, BdfDictionary metadata)
 			throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
-		try {
-			mergeGroupMetadata(txn, g, metadata);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> mergeGroupMetadata(txn, g, metadata));
 	}
 
 	@Override
@@ -263,13 +207,7 @@ class ClientHelperImpl implements ClientHelper {
 	@Override
 	public void mergeMessageMetadata(MessageId m, BdfDictionary metadata)
 			throws DbException, FormatException {
-		Transaction txn = db.startTransaction(false);
-		try {
-			mergeMessageMetadata(txn, m, metadata);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> mergeMessageMetadata(txn, m, metadata));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeTaskImpl.java

@@ -13,7 +13,6 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
@@ -158,7 +157,8 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 				streamWriterFactory.createContactExchangeStreamWriter(out,
 						alice ? aliceHeaderKey : bobHeaderKey);
 		RecordWriter recordWriter =
-				recordWriterFactory.createRecordWriter(streamWriter.getOutputStream());
+				recordWriterFactory
+						.createRecordWriter(streamWriter.getOutputStream());
 
 		// Derive the nonces to be signed
 		byte[] aliceNonce = crypto.mac(ALICE_NONCE_LABEL, masterSecret,
@@ -287,19 +287,14 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private ContactId addContact(Author remoteAuthor, long timestamp,
 			Map<TransportId, TransportProperties> remoteProperties)
 			throws DbException {
-		ContactId contactId;
-		Transaction txn = db.startTransaction(false);
-		try {
-			contactId = contactManager.addContact(txn, remoteAuthor,
+		return db.transactionWithResult(false, txn -> {
+			ContactId contactId = contactManager.addContact(txn, remoteAuthor,
 					localAuthor.getId(), masterSecret, timestamp, alice,
 					true, true);
 			transportPropertyManager.addRemoteProperties(txn, contactId,
 					remoteProperties);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return contactId;
+			return contactId;
+		});
 	}
 
 	private void tryToClose(DuplexTransportConnection conn) {

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -79,42 +79,21 @@ class ContactManagerImpl implements ContactManager {
 	public ContactId addContact(Author remote, AuthorId local, SecretKey master,
 			long timestamp, boolean alice, boolean verified, boolean active)
 			throws DbException {
-		ContactId c;
-		Transaction txn = db.startTransaction(false);
-		try {
-			c = addContact(txn, remote, local, master, timestamp, alice,
-					verified, active);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return c;
+		return db.transactionWithResult(false,
+				txn -> addContact(txn, remote, local, master, timestamp, alice,
+						verified, active));
 	}
 
 	@Override
 	public Contact getContact(ContactId c) throws DbException {
-		Contact contact;
-		Transaction txn = db.startTransaction(true);
-		try {
-			contact = db.getContact(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return contact;
+		return db.transactionWithResult(true, txn -> db.getContact(txn, c));
 	}
 
 	@Override
 	public Contact getContact(AuthorId remoteAuthorId, AuthorId localAuthorId)
 			throws DbException {
-		Transaction txn = db.startTransaction(true);
-		try {
-			Contact c = getContact(txn, remoteAuthorId, localAuthorId);
-			db.commitTransaction(txn);
-			return c;
-		} finally {
-			db.endTransaction(txn);
-		}
+		return db.transactionWithResult(true,
+				txn -> getContact(txn, remoteAuthorId, localAuthorId));
 	}
 
 	@Override
@@ -132,14 +111,8 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public Collection<Contact> getActiveContacts() throws DbException {
-		Collection<Contact> contacts;
-		Transaction txn = db.startTransaction(true);
-		try {
-			contacts = db.getContacts(txn);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		Collection<Contact> contacts =
+				db.transactionWithResult(true, db::getContacts);
 		List<Contact> active = new ArrayList<>(contacts.size());
 		for (Contact c : contacts) if (c.isActive()) active.add(c);
 		return active;
@@ -147,13 +120,7 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public void removeContact(ContactId c) throws DbException {
-		Transaction txn = db.startTransaction(false);
-		try {
-			removeContact(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> removeContact(txn, c));
 	}
 
 	@Override
@@ -188,15 +155,8 @@ class ContactManagerImpl implements ContactManager {
 	@Override
 	public boolean contactExists(AuthorId remoteAuthorId,
 			AuthorId localAuthorId) throws DbException {
-		boolean exists;
-		Transaction txn = db.startTransaction(true);
-		try {
-			exists = contactExists(txn, remoteAuthorId, localAuthorId);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return exists;
+		return db.transactionWithResult(true,
+				txn -> contactExists(txn, remoteAuthorId, localAuthorId));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/identity/IdentityManagerImpl.java

@@ -67,27 +67,16 @@ class IdentityManagerImpl implements IdentityManager {
 			LOG.info("No local author to store");
 			return;
 		}
-		Transaction txn = db.startTransaction(false);
-		try {
-			db.addLocalAuthor(txn, cached);
-			db.commitTransaction(txn);
-			LOG.info("Local author stored");
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> db.addLocalAuthor(txn, cached));
+		LOG.info("Local author stored");
 	}
 
 	@Override
 	public LocalAuthor getLocalAuthor() throws DbException {
 		if (cachedAuthor == null) {
-			Transaction txn = db.startTransaction(true);
-			try {
-				cachedAuthor = loadLocalAuthor(txn);
-				LOG.info("Local author loaded");
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			cachedAuthor =
+					db.transactionWithResult(true, this::loadLocalAuthor);
+			LOG.info("Local author loaded");
 		}
 		LocalAuthor cached = cachedAuthor;
 		if (cached == null) throw new AssertionError();

bramble-core/src/main/java/org/briarproject/bramble/lifecycle/LifecycleManagerImpl.java

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MigrationListener;
-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.lifecycle.LifecycleManager;
@@ -115,20 +114,16 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 			dbLatch.countDown();
 			eventBus.broadcast(new LifecycleEvent(STARTING_SERVICES));
 
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				for (Client c : clients) {
-					start = now();
+					long start1 = now();
 					c.createLocalState(txn);
 					if (LOG.isLoggable(FINE)) {
 						logDuration(LOG, "Starting client "
-								+ c.getClass().getSimpleName(), start);
+								+ c.getClass().getSimpleName(), start1);
 					}
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 			for (Service s : services) {
 				start = now();
 				s.startService();

bramble-core/src/main/java/org/briarproject/bramble/properties/TransportPropertyManagerImpl.java

@@ -142,15 +142,7 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public Map<TransportId, TransportProperties> getLocalProperties()
 			throws DbException {
-		Map<TransportId, TransportProperties> local;
-		Transaction txn = db.startTransaction(true);
-		try {
-			local = getLocalProperties(txn);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return local;
+		return db.transactionWithResult(true, this::getLocalProperties);
 	}
 
 	@Override
@@ -176,9 +168,8 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	public TransportProperties getLocalProperties(TransportId t)
 			throws DbException {
 		try {
-			TransportProperties p = null;
-			Transaction txn = db.startTransaction(true);
-			try {
+			return db.transactionWithResult(true, txn -> {
+				TransportProperties p = null;
 				// Find the latest local update
 				LatestUpdate latest = findLatest(txn, localGroup.getId(), t,
 						true);
@@ -188,11 +179,8 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 							latest.messageId);
 					p = parseProperties(message);
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
-			return p == null ? new TransportProperties() : p;
+				return p == null ? new TransportProperties() : p;
+			});
 		} catch (FormatException e) {
 			throw new DbException(e);
 		}
@@ -201,16 +189,12 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public Map<ContactId, TransportProperties> getRemoteProperties(
 			TransportId t) throws DbException {
-		Map<ContactId, TransportProperties> remote = new HashMap<>();
-		Transaction txn = db.startTransaction(true);
-		try {
+		return db.transactionWithResult(true, txn -> {
+			Map<ContactId, TransportProperties> remote = new HashMap<>();
 			for (Contact c : db.getContacts(txn))
 				remote.put(c.getId(), getRemoteProperties(txn, c, t));
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return remote;
+			return remote;
+		});
 	}
 
 	private TransportProperties getRemoteProperties(Transaction txn, Contact c,
@@ -234,23 +218,15 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	@Override
 	public TransportProperties getRemoteProperties(ContactId c, TransportId t)
 			throws DbException {
-		TransportProperties p;
-		Transaction txn = db.startTransaction(true);
-		try {
-			p = getRemoteProperties(txn, db.getContact(txn, c), t);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return p;
+		return db.transactionWithResult(true,
+				txn -> getRemoteProperties(txn, db.getContact(txn, c), t));
 	}
 
 	@Override
 	public void mergeLocalProperties(TransportId t, TransportProperties p)
 			throws DbException {
 		try {
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				// Merge the new properties with any existing properties
 				TransportProperties merged;
 				boolean changed;
@@ -287,10 +263,7 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 							db.removeMessage(txn, latest.messageId);
 					}
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 		} catch (FormatException e) {
 			throw new DbException(e);
 		}

bramble-core/src/main/java/org/briarproject/bramble/settings/SettingsManagerImpl.java

@@ -23,15 +23,8 @@ class SettingsManagerImpl implements SettingsManager {
 
 	@Override
 	public Settings getSettings(String namespace) throws DbException {
-		Settings s;
-		Transaction txn = db.startTransaction(true);
-		try {
-			s = db.getSettings(txn, namespace);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return s;
+		return db.transactionWithResult(true,
+				txn -> db.getSettings(txn, namespace));
 	}
 
 	@Override
@@ -42,12 +35,6 @@ class SettingsManagerImpl implements SettingsManager {
 
 	@Override
 	public void mergeSettings(Settings s, String namespace) throws DbException {
-		Transaction txn = db.startTransaction(false);
-		try {
-			db.mergeSettings(txn, s, namespace);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
+		db.transaction(false, txn -> db.mergeSettings(txn, s, namespace));
 	}
 }

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

@@ -1,11 +1,11 @@
 package org.briarproject.bramble.sync;
 
+import org.briarproject.bramble.api.Maybe;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 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.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -230,17 +230,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (interrupted) return;
 			if (!generateAckQueued.getAndSet(false)) throw new AssertionError();
 			try {
-				Ack a;
-				Transaction txn = db.startTransaction(false);
-				try {
-					a = db.generateAck(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				Maybe<Ack> a = db.transactionWithResult(false,
+						txn -> new Maybe<>(db.generateAck(txn, contactId,
+								MAX_MESSAGE_IDS)));
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated ack: " + (a != null));
-				if (a != null) writerTasks.add(new WriteAck(a));
+					LOG.info("Generated ack: " + a.isPresent());
+				if (a.isPresent()) writerTasks.add(new WriteAck(a.get()));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -275,19 +270,16 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateBatchQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Collection<Message> b;
-				Transaction txn = db.startTransaction(false);
-				try {
-					b = db.generateRequestedBatch(txn, contactId,
-							MAX_RECORD_PAYLOAD_BYTES, maxLatency);
+				Maybe<Collection<Message>>
+						b = db.transactionWithResult(false, txn -> {
+					Collection<Message> batch = db.generateRequestedBatch(txn,
+							contactId, MAX_RECORD_PAYLOAD_BYTES, maxLatency);
 					setNextSendTime(db.getNextSendTime(txn, contactId));
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+					return new Maybe<>(batch);
+				});
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated batch: " + (b != null));
-				if (b != null) writerTasks.add(new WriteBatch(b));
+					LOG.info("Generated batch: " + b.isPresent());
+				if (b.isPresent()) writerTasks.add(new WriteBatch(b.get()));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -322,19 +314,15 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateOfferQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Offer o;
-				Transaction txn = db.startTransaction(false);
-				try {
-					o = db.generateOffer(txn, contactId, MAX_MESSAGE_IDS,
-							maxLatency);
+				Maybe<Offer> o = db.transactionWithResult(false, txn -> {
+					Offer offer = db.generateOffer(txn, contactId,
+							MAX_MESSAGE_IDS, maxLatency);
 					setNextSendTime(db.getNextSendTime(txn, contactId));
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+					return new Maybe<>(offer);
+				});
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated offer: " + (o != null));
-				if (o != null) writerTasks.add(new WriteOffer(o));
+					LOG.info("Generated offer: " + o.isPresent());
+				if (o.isPresent()) writerTasks.add(new WriteOffer(o.get()));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -369,17 +357,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 			if (!generateRequestQueued.getAndSet(false))
 				throw new AssertionError();
 			try {
-				Request r;
-				Transaction txn = db.startTransaction(false);
-				try {
-					r = db.generateRequest(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				Maybe<Request> r = db.transactionWithResult(false,
+						txn -> new Maybe<>(db.generateRequest(txn, contactId,
+								MAX_MESSAGE_IDS)));
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated request: " + (r != null));
-				if (r != null) writerTasks.add(new WriteRequest(r));
+					LOG.info("Generated request: " + r.isPresent());
+				if (r.isPresent()) writerTasks.add(new WriteRequest(r.get()));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();

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

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 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.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -120,13 +119,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
-				try {
-					db.receiveAck(txn, contactId, ack);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				db.transaction(false,
+						txn -> db.receiveAck(txn, contactId, ack));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -146,13 +140,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
-				try {
-					db.receiveMessage(txn, contactId, message);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				db.transaction(false,
+						txn -> db.receiveMessage(txn, contactId, message));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -172,13 +161,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
-				try {
-					db.receiveOffer(txn, contactId, offer);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				db.transaction(false,
+						txn -> db.receiveOffer(txn, contactId, offer));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -198,13 +182,8 @@ class IncomingSession implements SyncSession, EventListener {
 		@Override
 		public void run() {
 			try {
-				Transaction txn = db.startTransaction(false);
-				try {
-					db.receiveRequest(txn, contactId, request);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				db.transaction(false,
+						txn -> db.receiveRequest(txn, contactId, request));
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();

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

@@ -1,11 +1,11 @@
 package org.briarproject.bramble.sync;
 
+import org.briarproject.bramble.api.Maybe;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
 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.db.Transaction;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventListener;
@@ -47,7 +47,8 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private static final Logger LOG =
 			Logger.getLogger(SimplexOutgoingSession.class.getName());
 
-	private static final ThrowingRunnable<IOException> CLOSE = () -> {};
+	private static final ThrowingRunnable<IOException> CLOSE = () -> {
+	};
 
 	private final DatabaseComponent db;
 	private final Executor dbExecutor;
@@ -128,18 +129,13 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		public void run() {
 			if (interrupted) return;
 			try {
-				Ack a;
-				Transaction txn = db.startTransaction(false);
-				try {
-					a = db.generateAck(txn, contactId, MAX_MESSAGE_IDS);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				Maybe<Ack> a = db.transactionWithResult(false,
+						txn -> new Maybe<>(db.generateAck(txn, contactId,
+								MAX_MESSAGE_IDS)));
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated ack: " + (a != null));
-				if (a == null) decrementOutstandingQueries();
-				else writerTasks.add(new WriteAck(a));
+					LOG.info("Generated ack: " + a.isPresent());
+				if (a.isPresent()) writerTasks.add(new WriteAck(a.get()));
+				else decrementOutstandingQueries();
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();
@@ -172,19 +168,13 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		public void run() {
 			if (interrupted) return;
 			try {
-				Collection<Message> b;
-				Transaction txn = db.startTransaction(false);
-				try {
-					b = db.generateBatch(txn, contactId,
-							MAX_RECORD_PAYLOAD_BYTES, maxLatency);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				Maybe<Collection<Message>> b = db.transactionWithResult(false,
+						txn -> new Maybe<>(db.generateBatch(txn, contactId,
+								MAX_RECORD_PAYLOAD_BYTES, maxLatency)));
 				if (LOG.isLoggable(INFO))
-					LOG.info("Generated batch: " + (b != null));
-				if (b == null) decrementOutstandingQueries();
-				else writerTasks.add(new WriteBatch(b));
+					LOG.info("Generated batch: " + b.isPresent());
+				if (b.isPresent()) writerTasks.add(new WriteBatch(b.get()));
+				else decrementOutstandingQueries();
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 				interrupt();

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

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.sync;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.db.DbException;
@@ -97,14 +98,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void validateOutstandingMessages() {
 		try {
-			Queue<MessageId> unvalidated = new LinkedList<>();
-			Transaction txn = db.startTransaction(true);
-			try {
-				unvalidated.addAll(db.getMessagesToValidate(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			Queue<MessageId> unvalidated = new LinkedList<>(
+					db.transactionWithResult(true, db::getMessagesToValidate));
 			validateNextMessageAsync(unvalidated);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -119,18 +114,14 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void validateNextMessage(Queue<MessageId> unvalidated) {
 		try {
-			Message m;
-			Group g;
-			Transaction txn = db.startTransaction(true);
-			try {
+			Pair<Message, Group> mg = db.transactionWithResult(true, txn -> {
 				MessageId id = unvalidated.poll();
-				m = db.getMessage(txn, id);
-				g = db.getGroup(txn, m.getGroupId());
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
-			validateMessageAsync(m, g);
+				if (id == null) throw new AssertionError();
+				Message m = db.getMessage(txn, id);
+				Group g = db.getGroup(txn, m.getGroupId());
+				return new Pair<>(m, g);
+			});
+			validateMessageAsync(mg.getFirst(), mg.getSecond());
 			validateNextMessageAsync(unvalidated);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before validation");
@@ -150,14 +141,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void deliverOutstandingMessages() {
 		try {
-			Queue<MessageId> pending = new LinkedList<>();
-			Transaction txn = db.startTransaction(true);
-			try {
-				pending.addAll(db.getPendingMessages(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			Queue<MessageId> pending = new LinkedList<>(
+					db.transactionWithResult(true, db::getPendingMessages));
 			deliverNextPendingMessageAsync(pending);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -172,12 +157,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void deliverNextPendingMessage(Queue<MessageId> pending) {
 		try {
-			boolean anyInvalid = false, allDelivered = true;
-			Queue<MessageId> toShare = null;
-			Queue<MessageId> invalidate = null;
-			Transaction txn = db.startTransaction(false);
-			try {
+			Queue<MessageId> toShare = new LinkedList<>();
+			Queue<MessageId> invalidate = new LinkedList<>();
+			db.transaction(false, txn -> {
+				boolean anyInvalid = false, allDelivered = true;
 				MessageId id = pending.poll();
+				if (id == null) throw new AssertionError();
 				// Check if message is still pending
 				if (db.getMessageState(txn, id) == PENDING) {
 					// Check if dependencies are valid and delivered
@@ -189,7 +174,7 @@ class ValidationManagerImpl implements ValidationManager, Service,
 					}
 					if (anyInvalid) {
 						invalidateMessage(txn, id);
-						invalidate = getDependentsToInvalidate(txn, id);
+						addDependentsToInvalidate(txn, id, invalidate);
 					} else if (allDelivered) {
 						Message m = db.getMessage(txn, id);
 						Group g = db.getGroup(txn, m.getGroupId());
@@ -200,22 +185,19 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						DeliveryResult result =
 								deliverMessage(txn, m, c, majorVersion, meta);
 						if (result.valid) {
-							pending.addAll(getPendingDependents(txn, id));
+							addPendingDependents(txn, id, pending);
 							if (result.share) {
 								db.setMessageShared(txn, id);
-								toShare = new LinkedList<>(states.keySet());
+								toShare.addAll(states.keySet());
 							}
 						} else {
-							invalidate = getDependentsToInvalidate(txn, id);
+							addDependentsToInvalidate(txn, id, invalidate);
 						}
 					}
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
-			if (invalidate != null) invalidateNextMessageAsync(invalidate);
-			if (toShare != null) shareNextMessageAsync(toShare);
+			});
+			if (!invalidate.isEmpty()) invalidateNextMessageAsync(invalidate);
+			if (!toShare.isEmpty()) shareNextMessageAsync(toShare);
 			deliverNextPendingMessageAsync(pending);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before delivery");
@@ -264,12 +246,11 @@ class ValidationManagerImpl implements ValidationManager, Service,
 			MessageContext context) {
 		try {
 			MessageId id = m.getId();
-			boolean anyInvalid = false, allDelivered = true;
-			Queue<MessageId> invalidate = null;
-			Queue<MessageId> pending = null;
-			Queue<MessageId> toShare = null;
-			Transaction txn = db.startTransaction(false);
-			try {
+			Queue<MessageId> invalidate = new LinkedList<>();
+			Queue<MessageId> pending = new LinkedList<>();
+			Queue<MessageId> toShare = new LinkedList<>();
+			db.transaction(false, txn -> {
+				boolean anyInvalid = false, allDelivered = true;
 				// Check if message has any dependencies
 				Collection<MessageId> dependencies = context.getDependencies();
 				if (!dependencies.isEmpty()) {
@@ -285,7 +266,7 @@ class ValidationManagerImpl implements ValidationManager, Service,
 				if (anyInvalid) {
 					if (db.getMessageState(txn, id) != INVALID) {
 						invalidateMessage(txn, id);
-						invalidate = getDependentsToInvalidate(txn, id);
+						addDependentsToInvalidate(txn, id, invalidate);
 					}
 				} else {
 					Metadata meta = context.getMetadata();
@@ -294,25 +275,22 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						DeliveryResult result =
 								deliverMessage(txn, m, c, majorVersion, meta);
 						if (result.valid) {
-							pending = getPendingDependents(txn, id);
+							addPendingDependents(txn, id, pending);
 							if (result.share) {
 								db.setMessageShared(txn, id);
-								toShare = new LinkedList<>(dependencies);
+								toShare.addAll(dependencies);
 							}
 						} else {
-							invalidate = getDependentsToInvalidate(txn, id);
+							addDependentsToInvalidate(txn, id, invalidate);
 						}
 					} else {
 						db.setMessageState(txn, id, PENDING);
 					}
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
-			if (invalidate != null) invalidateNextMessageAsync(invalidate);
-			if (pending != null) deliverNextPendingMessageAsync(pending);
-			if (toShare != null) shareNextMessageAsync(toShare);
+			});
+			if (!invalidate.isEmpty()) invalidateNextMessageAsync(invalidate);
+			if (!pending.isEmpty()) deliverNextPendingMessageAsync(pending);
+			if (!toShare.isEmpty()) shareNextMessageAsync(toShare);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed during validation");
 		} catch (NoSuchGroupException e) {
@@ -342,14 +320,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	}
 
 	@DatabaseExecutor
-	private Queue<MessageId> getPendingDependents(Transaction txn, MessageId m)
-			throws DbException {
-		Queue<MessageId> pending = new LinkedList<>();
+	private void addPendingDependents(Transaction txn, MessageId m,
+			Queue<MessageId> pending) throws DbException {
 		Map<MessageId, State> states = db.getMessageDependents(txn, m);
 		for (Entry<MessageId, State> e : states.entrySet()) {
 			if (e.getValue() == PENDING) pending.add(e.getKey());
 		}
-		return pending;
 	}
 
 	private void shareOutstandingMessagesAsync() {
@@ -359,14 +335,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void shareOutstandingMessages() {
 		try {
-			Queue<MessageId> toShare = new LinkedList<>();
-			Transaction txn = db.startTransaction(true);
-			try {
-				toShare.addAll(db.getMessagesToShare(txn));
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			Queue<MessageId> toShare = new LinkedList<>(
+					db.transactionWithResult(true, db::getMessagesToShare));
 			shareNextMessageAsync(toShare);
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
@@ -387,15 +357,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void shareNextMessage(Queue<MessageId> toShare) {
 		try {
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				MessageId id = toShare.poll();
+				if (id == null) throw new AssertionError();
 				db.setMessageShared(txn, id);
 				toShare.addAll(db.getMessageDependencies(txn, id).keySet());
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 			shareNextMessageAsync(toShare);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before sharing");
@@ -416,17 +383,14 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void invalidateNextMessage(Queue<MessageId> invalidate) {
 		try {
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				MessageId id = invalidate.poll();
+				if (id == null) throw new AssertionError();
 				if (db.getMessageState(txn, id) != INVALID) {
 					invalidateMessage(txn, id);
-					invalidate.addAll(getDependentsToInvalidate(txn, id));
+					addDependentsToInvalidate(txn, id, invalidate);
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 			invalidateNextMessageAsync(invalidate);
 		} catch (NoSuchMessageException e) {
 			LOG.info("Message removed before invalidation");
@@ -445,14 +409,12 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	}
 
 	@DatabaseExecutor
-	private Queue<MessageId> getDependentsToInvalidate(Transaction txn,
-			MessageId m) throws DbException {
-		Queue<MessageId> invalidate = new LinkedList<>();
+	private void addDependentsToInvalidate(Transaction txn,
+			MessageId m, Queue<MessageId> invalidate) throws DbException {
 		Map<MessageId, State> states = db.getMessageDependents(txn, m);
 		for (Entry<MessageId, State> e : states.entrySet()) {
 			if (e.getValue() != INVALID) invalidate.add(e.getKey());
 		}
-		return invalidate;
 	}
 
 	@Override
@@ -472,14 +434,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void loadGroupAndValidate(Message m) {
 		try {
-			Group g;
-			Transaction txn = db.startTransaction(true);
-			try {
-				g = db.getGroup(txn, m.getGroupId());
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			Group g = db.transactionWithResult(true,
+					txn -> db.getGroup(txn, m.getGroupId()));
 			validateMessageAsync(m, g);
 		} catch (NoSuchGroupException e) {
 			LOG.info("Group removed before validation");

bramble-core/src/main/java/org/briarproject/bramble/transport/KeyManagerImpl.java

@@ -72,8 +72,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 		for (DuplexPluginFactory f : pluginConfig.getDuplexFactories())
 			transports.put(f.getId(), f.getMaxLatency());
 		try {
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				for (Contact c : db.getContacts(txn))
 					if (c.isActive()) activeContacts.put(c.getId(), true);
 				for (Entry<TransportId, Integer> e : transports.entrySet())
@@ -85,10 +84,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 					managers.put(e.getKey(), m);
 					m.start(txn);
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 		} catch (DbException e) {
 			throw new ServiceException(e);
 		}
@@ -141,15 +137,8 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx;
-		Transaction txn = db.startTransaction(false);
-		try {
-			ctx = m.getStreamContext(txn, c);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return ctx;
+		return db.transactionWithResult(false,
+				txn -> m.getStreamContext(txn, c));
 	}
 
 	@Override
@@ -160,15 +149,8 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			if (LOG.isLoggable(INFO)) LOG.info("No key manager for " + t);
 			return null;
 		}
-		StreamContext ctx;
-		Transaction txn = db.startTransaction(false);
-		try {
-			ctx = m.getStreamContext(txn, tag);
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
-		}
-		return ctx;
+		return db.transactionWithResult(false,
+				txn -> m.getStreamContext(txn, tag));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManagerImpl.java

@@ -162,13 +162,7 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 	private void rotateKeys() {
 		dbExecutor.execute(() -> {
 			try {
-				Transaction txn = db.startTransaction(false);
-				try {
-					rotateKeys(txn);
-					db.commitTransaction(txn);
-				} finally {
-					db.endTransaction(txn);
-				}
+				db.transaction(false, this::rotateKeys);
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 			}

bramble-core/src/main/java/org/briarproject/bramble/versioning/ClientVersioningManagerImpl.java

@@ -123,16 +123,12 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 		List<ClientVersion> versions = new ArrayList<>(clients);
 		Collections.sort(versions);
 		try {
-			Transaction txn = db.startTransaction(false);
-			try {
+			db.transaction(false, txn -> {
 				if (updateClientVersions(txn, versions)) {
 					for (Contact c : db.getContacts(txn))
 						clientVersionsUpdated(txn, c, versions);
 				}
-				db.commitTransaction(txn);
-			} finally {
-				db.endTransaction(txn);
-			}
+			});
 		} catch (DbException e) {
 			throw new ServiceException(e);
 		}