Add method for getting cooked message from DB.

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

@@ -298,6 +298,15 @@ interface Database<T> {
 	 */
 	Collection<LocalAuthor> getLocalAuthors(T txn) throws DbException;
 
+	/**
+	 * Returns the message with the given ID.
+	 * <p/>
+	 * Read-only.
+	 *
+	 * @throws MessageDeletedException if the message has been deleted
+	 */
+	Message getMessage(T txn, MessageId m) throws DbException;
+
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
 	 * For missing dependencies and dependencies in other groups, the state

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

@@ -457,6 +457,15 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getLocalAuthors(txn);
 	}
 
+	@Override
+	public Message getMessage(Transaction transaction, MessageId m)
+			throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsMessage(txn, m))
+			throw new NoSuchMessageException();
+		return db.getMessage(txn, m);
+	}
+
 	@Override
 	public Collection<MessageId> getMessageIds(Transaction transaction,
 			GroupId g) throws DbException {

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

@@ -1483,6 +1483,32 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public Message getMessage(Connection txn, MessageId m) throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT groupId, timestamp, raw FROM messages"
+					+ " WHERE messageId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, m.getBytes());
+			rs = ps.executeQuery();
+			if (!rs.next()) throw new DbStateException();
+			GroupId g = new GroupId(rs.getBytes(1));
+			long timestamp = rs.getLong(2);
+			byte[] raw = rs.getBytes(3);
+			if (rs.next()) throw new DbStateException();
+			rs.close();
+			ps.close();
+			if (raw == null) throw new MessageDeletedException();
+			return new Message(m, g, timestamp, raw);
+		} catch (SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public Collection<MessageId> getMessageIds(Connection txn, GroupId g)
 			throws DbException {