add transactional versions of some API calls

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactManager.java

@@ -107,6 +107,12 @@ public interface ContactManager {
 	 */
 	String getHandshakeLink() throws DbException;
 
+	/**
+	 * Returns the handshake link that needs to be sent to a contact we want
+	 * to add.
+	 */
+	String getHandshakeLink(Transaction txn) throws DbException;
+
 	/**
 	 * Creates a {@link PendingContact} from the given handshake link and
 	 * alias, adds it to the database and returns it.

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

@@ -121,8 +121,12 @@ class ContactManagerImpl implements ContactManager, EventListener {
 
 	@Override
 	public String getHandshakeLink() throws DbException {
-		KeyPair keyPair = db.transactionWithResult(true,
+		return db.transactionWithResult(true, this::getHandshakeLink);
-				identityManager::getHandshakeKeys);
+	}
+
+	@Override
+	public String getHandshakeLink(Transaction txn) throws DbException {
+		KeyPair keyPair = identityManager.getHandshakeKeys(txn);
 		return pendingContactFactory.createHandshakeLink(keyPair.getPublic());
 	}
 

briar-api/src/main/java/org/briarproject/briar/api/conversation/ConversationManager.java

@@ -38,6 +38,15 @@ public interface ConversationManager {
 	Collection<ConversationMessageHeader> getMessageHeaders(ContactId c)
 			throws DbException;
 
+	/**
+	 * Returns the headers of all messages in the given private conversation.
+	 * <p>
+	 * Only {@link MessagingManager} returns only headers.
+	 * The others also return the message text.
+	 */
+	Collection<ConversationMessageHeader> getMessageHeaders(Transaction txn, ContactId c)
+			throws DbException;
+
 	/**
 	 * Returns the unified group count for all private conversation messages.
 	 */
@@ -72,6 +81,9 @@ public interface ConversationManager {
 	void setReadFlag(GroupId g, MessageId m, boolean read)
 			throws DbException;
 
+	void setReadFlag(Transaction txn, GroupId g, MessageId m, boolean read)
+			throws DbException;
+
 	/**
 	 * Returns a timestamp for an outgoing message, which is later than the
 	 * timestamp of any message in the conversation with the given contact.

briar-api/src/main/java/org/briarproject/briar/api/messaging/MessagingManager.java

@@ -74,6 +74,13 @@ public interface MessagingManager extends ConversationClient {
 	@Nullable
 	String getMessageText(MessageId m) throws DbException;
 
+	/**
+	 * Returns the text of the private message with the given ID, or null if
+	 * the private message has no text.
+	 */
+	@Nullable
+	String getMessageText(Transaction txn, MessageId m) throws DbException;
+
 	/**
 	 * Returns the private message format supported by the given contact.
 	 */

briar-core/src/main/java/org/briarproject/briar/conversation/ConversationManagerImpl.java

@@ -58,15 +58,16 @@ class ConversationManagerImpl implements ConversationManager {
 	@Override
 	public Collection<ConversationMessageHeader> getMessageHeaders(ContactId c)
 			throws DbException {
+		return db.transactionWithResult(true,
+				txn -> getMessageHeaders(txn, c));
+	}
+
+	@Override
+	public Collection<ConversationMessageHeader> getMessageHeaders(Transaction txn, ContactId c)
+			throws DbException {
 		List<ConversationMessageHeader> messages = new ArrayList<>();
-		Transaction txn = db.startTransaction(true);
+		for (ConversationClient client : clients) {
-		try {
+			messages.addAll(client.getMessageHeaders(txn, c));
-			for (ConversationClient client : clients) {
-				messages.addAll(client.getMessageHeaders(txn, c));
-			}
-			db.commitTransaction(txn);
-		} finally {
-			db.endTransaction(txn);
 		}
 		return messages;
 	}
@@ -125,10 +126,14 @@ class ConversationManagerImpl implements ConversationManager {
 	@Override
 	public void setReadFlag(GroupId g, MessageId m, boolean read)
 			throws DbException {
-		db.transaction(false, txn -> {
+		db.transaction(false, txn -> setReadFlag(txn, g, m, read));
-			boolean wasRead = messageTracker.setReadFlag(txn, g, m, read);
+	}
-			if (read && !wasRead) db.startCleanupTimer(txn, m);
+
-		});
+	@Override
+	public void setReadFlag(Transaction txn, GroupId g, MessageId m, boolean read)
+			throws DbException {
+		boolean wasRead = messageTracker.setReadFlag(txn, g, m, read);
+		if (read && !wasRead) db.startCleanupTimer(txn, m);
 	}
 
 	@Override

briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java

@@ -466,8 +466,14 @@ class MessagingManagerImpl implements MessagingManager, IncomingMessageHook,
 
 	@Override
 	public String getMessageText(MessageId m) throws DbException {
+		return db.transactionWithNullableResult(true, txn ->
+				getMessageText(txn, m));
+	}
+
+	@Override
+	public String getMessageText(Transaction txn, MessageId m) throws DbException {
 		try {
-			BdfList body = clientHelper.getMessageAsList(m);
+			BdfList body = clientHelper.getMessageAsList(txn, m);
 			if (body.size() == 1) return body.getString(0); // Legacy format
 			else return body.getOptionalString(1);
 		} catch (FormatException e) {