Add a DB method for checking whether transport keys exist.

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

@@ -215,6 +215,16 @@ interface Database<T> {
 	 */
 	boolean containsTransport(T txn, TransportId t) throws DbException;
 
+	/**
+	 * Returns true if the database contains keys for communicating with the
+	 * given contact over the given transport. Handshake mode and rotation mode
+	 * keys are included, whether activated or not.
+	 * <p/>
+	 * Read-only.
+	 */
+	boolean containsTransportKeys(T txn, ContactId c, TransportId t)
+			throws DbException;
+
 	/**
 	 * Returns true if the database contains the given message, the message is
 	 * shared, and the visibility of the message's group to the given contact

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

@@ -371,6 +371,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.containsPendingContact(txn, p);
 	}
 
+	@Override
+	public boolean containsTransportKeys(Transaction transaction, ContactId c,
+			TransportId t) throws DbException {
+		T txn = unbox(transaction);
+		return db.containsTransportKeys(txn, c, t);
+	}
+
 	@Override
 	public void deleteMessage(Transaction transaction, MessageId m)
 			throws DbException {

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

@@ -1277,6 +1277,29 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public boolean containsTransportKeys(Connection txn, ContactId c,
+			TransportId t) throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT NULL FROM outgoingKeys"
+					+ " WHERE contactId = ? AND transportId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setString(2, t.getString());
+			rs = ps.executeQuery();
+			boolean found = rs.next();
+			rs.close();
+			ps.close();
+			return found;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public boolean containsVisibleMessage(Connection txn, ContactId c,
 			MessageId m) throws DbException {