public enum ConnectionStatus {
    IDLE(0),
    CONNECTED(1),
    DISCONNECTED(2),
    CONNECTING(3),
    FAILURE(4);
}

public enum ConversationType {
    UNKNOWN(0),
    /// 单聊
    PRIVATE(1),
    /// 群组
    GROUP(2),
    /// 聊天室
    CHATROOM(3),
    /// 系统会话
    SYSTEM(4);
}

public enum PullDirection {
    NEWER, OLDER
}