virtual QList<Message> requestMsgs(UserId user, BufferId bufferId, QDateTime since, int offset = -1);
virtual QList<Message> requestMsgRange(UserId user, BufferId bufferId, int first, int last);
virtual QList<Message> requestMsgs(UserId user, BufferId bufferId, QDateTime since, int offset = -1);
virtual QList<Message> requestMsgRange(UserId user, BufferId bufferId, int first, int last);