// 启动服务器
        private void btnFtpServerStartStop_Click(object sender, EventArgs e)
        {
            if (myTcpListener == null)
            {
                listenThread = new Thread(ListenClientConnect);
                listenThread.IsBackground = true;
                listenThread.Start();

                lstboxStatus.Enabled = true;
                lstboxStatus.Items.Clear();
                lstboxStatus.Items.Add("启动Ftp服务...");
                btnFtpServerStartStop.Text = "停止";
            }
            else
            {
                myTcpListener.Stop();
                myTcpListener = null;
                listenThread.Abort();
                lstboxStatus.Items.Add("Ftp服务已停止！");
                lstboxStatus.TopIndex = lstboxStatus.Items.Count - 1;

                btnFtpServerStartStop.Text = "启动";
            }
        }

        // 监听端口，处理客户端连接
        private void ListenClientConnect()
        {
            myTcpListener = new TcpListener(IPAddress.Parse(tbxFtpServerIp.Text), int.Parse(tbxFtpServerPort.Text));
            // 开始监听传入的请求
            myTcpListener.Start();
            AddInfo("启动成功！");
            AddInfo("Ftp服务运行中...[单机”停止“退出]");
            while (true)
            {
                try
                {
                    // 接收连接请求
                    TcpClient tcpClient = myTcpListener.AcceptTcpClient();
                    AddInfo(string.Format("客户端（{0}）与本机（{1}）建立Ftp连接", tcpClient.Client.RemoteEndPoint, myTcpListener.LocalEndpoint));
                    User user = new User();
                    user.commandSession = new UserSeesion(tcpClient);
                    user.workDir = tbxFtpRoot.Text;
                    Thread t = new Thread(UserProcessing);
                    t.IsBackground = true;
                    t.Start(user);
                }
                catch
                {
                    break;
                }
            }
        }

        // 处理客户端用户请求
        private void UserProcessing(object obj)
        {
            User user = (User)obj;
            string sendString = "220 FTP Server v1.0";
            RepleyCommandToUser(user, sendString);
            while (true)
            {
                string receiveString = null;
                try
                {
                    // 读取客户端发来的请求信息
                    receiveString = user.commandSession.streamReader.ReadLine();
                }
                catch(Exception ex)
                {
                    if (user.commandSession.tcpClient.Connected == false)
                    {
                        AddInfo(string.Format("客户端({0}断开连接！)", user.commandSession.tcpClient.Client.RemoteEndPoint));
                    }
                    else
                    {
                        AddInfo("接收命令失败！" + ex.Message);
                    }

                    break;
                }

                if (receiveString == null)
                {
                    AddInfo("接收字符串为null,结束线程！");
                    break;
                }

                AddInfo(string.Format("来自{0}：[{1}]", user.commandSession.tcpClient.Client.RemoteEndPoint, receiveString));
                
                // 分解客户端发来的控制信息中的命令和参数
                string command = receiveString;
                string param = string.Empty;
                int index = receiveString.IndexOf(' ');
                if (index != -1)
                {
                    command = receiveString.Substring(0, index).ToUpper();
                    param = receiveString.Substring(command.Length).Trim();
                }

                // 处理不需登录即可响应的命令（这里只处理QUIT）
                if (command == "QUIT")
                {
                    // 关闭TCP连接并释放与其关联的所有资源
                    user.commandSession.Close();
                    return;
                }
                else
                {
                    switch (user.loginOK)
                    {
                        // 等待用户输入用户名：
                        case 0:
                            CommandUser(user, command, param);
                            break;

                        // 等待用户输入密码
                        case 1:
                            CommandPassword(user, command, param);
                            break;

                        // 用户名和密码验证正确后登陆
                        case 2:
                            switch (command)
                            {
                                case "CWD":
                                    CommandCWD(user, param);
                                    break;
                                case "PWD":
                                    CommandPWD(user);
                                    break;
                                case "PASV":
                                    CommandPASV(user);
                                    break;
                                case "PORT":
                                    CommandPORT(user, param);
                                    break;
                                case "LIST":
                                    CommandLIST(user, param);
                                    break;
                                case "NLIST":
                                    CommandLIST(user, param);
                                    break;
                                // 处理下载文件命令
                                case "RETR":
                                    CommandRETR(user, param);
                                    break;
                                // 处理上传文件命令
                                case "STOR":
                                    CommandSTOR(user, param);
                                    break;
                                // 处理删除命令
                                case "DELE":
                                    CommandDELE(user, param);
                                    break;
                                // 使用Type命令在ASCII和二进制模式进行变换
                                case "TYPE":
                                    CommandTYPE(user, param);
                                    break;
                                default:
                                    sendString = "502 command is not implemented.";
                                    RepleyCommandToUser(user, sendString);
                                    break;
                            }

                            break;
                    }          
                }
            }       
        }