请大家帮写用socket检测FTP上目录/文件是否存在的代码

Question

我从网上找了好些FTP的代码，测试了一下，就socket的最快。其它的代码，不知为何，在第一次连接FTP时都慢，有时长达一分钟，之后还行。 用SOCKET的就没这问题。 
下面是找到的SOCKET操作FTP的源码，但是它没有检测ftp上的目录或文件是否存在的功能，而我很需要这个，能不能请大家帮写一下，谢谢。using System;
using System.Net;
using System.IO;
using System.Text;
using System.Net.Sockets;
namespace FTP
{
    /// <summary>
    /// FTPClient 的摘要说明。
    /// </summary>
    public class FTPClient
    {
        #region 构造函数
        /// <summary>
        /// 缺省构造函数
        /// </summary>
        public FTPClient()
        {
            strRemoteHost = "";
            strRemotePath = "";
            strRemoteUser = "";
            strRemotePass = "";
            strRemotePort = 21;
            bConnected = false;
        } /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="remoteHost"></param>
        /// <param name="remotePath"></param>
        /// <param name="remoteUser"></param>
        /// <param name="remotePass"></param>
        /// <param name="remotePort"></param>
        public FTPClient(string remoteHost, string remotePath, string remoteUser, string remotePass, int remotePort)
        {
            strRemoteHost = remoteHost;
            strRemotePath = remotePath;
            strRemoteUser = remoteUser;
            strRemotePass = remotePass;
            strRemotePort = remotePort;
            Connect();
        }
        #endregion
        #region 登陆
        /// <summary>
        /// FTP服务器IP地址
        /// </summary>
        private string strRemoteHost;
        public string RemoteHost
        {
            get
            {
                return strRemoteHost;
            }
            set
            {
                strRemoteHost = value;
            }
        }
        /// <summary>
        /// FTP服务器端口
        /// </summary>
        private int strRemotePort;
        public int RemotePort
        {
            get
            {
                return strRemotePort;
            }
            set
            {
                strRemotePort = value;
            }
        }
        /// <summary>
        /// 当前服务器目录
        /// </summary>
        private string strRemotePath;
        public string RemotePath
        {
            get
            {
                return strRemotePath;
            }
            set
            {
                strRemotePath = value;
            }
        }
        /// <summary>
        /// 登录用户账号
        /// </summary>
        private string strRemoteUser;
        public string RemoteUser
        {
            set
            {
                strRemoteUser = value;
            }
        }
        /// <summary>
        /// 用户登录密码
        /// </summary>
        private string strRemotePass;
        public string RemotePass
        {
            set
            {
                strRemotePass = value;
            }
        } /// <summary>
        /// 是否登录
        /// </summary>
        private Boolean bConnected;
        public bool Connected
        {
            get
            {
                return bConnected;
            }
        }
        #endregion
        #region 链接
        /// <summary>
        /// 建立连接 
        /// </summary>
        public void Connect()
        {
            socketControl = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IPEndPoint ep = new IPEndPoint(IPAddress.Parse(RemoteHost), strRemotePort);
            // 链接
            try
            {
                socketControl.Connect(ep);
            }
            catch (Exception)
            {
                throw new IOException("Couldn't connect to remote server");
            }   // 获取应答码
            ReadReply();
            if (iReplyCode != 220)
            {
                DisConnect();
                throw new IOException(strReply.Substring(4));
            }   // 登陆
            SendCommand("USER " + strRemoteUser);
            if (!(iReplyCode == 331 || iReplyCode == 230))
            {
                CloseSocketConnect();//关闭连接
                throw new IOException(strReply.Substring(4));
            }
            if (iReplyCode != 230)
            {
                SendCommand("PASS " + strRemotePass);
                if (!(iReplyCode == 230 || iReplyCode == 202))
                {
                    CloseSocketConnect();//关闭连接
                    throw new IOException(strReply.Substring(4));
                }
            }
            bConnected = true;   // 切换到目录
            ChDir(strRemotePath);
        }
        /// <summary>
        /// 关闭连接
        /// </summary>
        public void DisConnect()
        {
            if (socketControl != null)
            {
                SendCommand("QUIT");
            }
            CloseSocketConnect();
        }
        #endregion
        #region 传输模式 /// <summary>
        /// 传输模式:二进制类型、ASCII类型
        /// </summary>
        public enum TransferType { Binary, ASCII }; /// <summary>
        /// 设置传输模式
        /// </summary>
        /// <param name="ttType">传输模式</param>
        public void SetTransferType(TransferType ttType)
        {
            if (ttType == TransferType.Binary)
            {
                SendCommand("TYPE I");//binary类型传输
            }
            else
            {
                SendCommand("TYPE A");//ASCII类型传输
            }
            if (iReplyCode != 200)
            {
                throw new IOException(strReply.Substring(4));
            }
            else
            {
                trType = ttType;
            }
        }
        /// <summary>
        /// 获得传输模式
        /// </summary>
        /// <returns>传输模式</returns>
        public TransferType GetTransferType()
        {
            return trType;
        }        #endregion
        #region 文件操作
        /// <summary>
        /// 获得文件列表
        /// </summary>
        /// <param name="strMask">文件名的匹配字符串</param>
        /// <returns></returns>
        public string[] Dir(string strMask)
        {
            // 建立链接
            if (!bConnected)
            {
                Connect();
            }   //建立进行数据连接的socket
            Socket socketData = CreateDataSocket();            //传送命令
            SendCommand("NLST " + strMask);   //分析应答代码
            if (!(iReplyCode == 150 || iReplyCode == 125 || iReplyCode == 226))
            {
                throw new IOException(strReply.Substring(4));
            }   //获得结果
            strMsg = "";
            while (true)
            {
                int iBytes = socketData.Receive(buffer, buffer.Length, 0);
                strMsg += ASCII.GetString(buffer, 0, iBytes);
                if (iBytes < buffer.Length)
                {
                    break;
                }
            }
            char[] seperator = { '\n' };
            string[] strsFileList = strMsg.Split(seperator);
            socketData.Close();//数据socket关闭时也会有返回码
            if (iReplyCode != 226)
            {
                ReadReply();
                if (iReplyCode != 226)
                {
                    throw new IOException(strReply.Substring(4));
                }
            }
            return strsFileList;
        }
        /// <summary>
        /// 获取文件大小
        /// </summary>
        /// <param name="strFileName">文件名</param>
        /// <returns>文件大小</returns>
      
        #endregion
        #region 目录操作
        /// <summary>
        /// 创建目录
        /// </summary>
        /// <param name="strDirName">目录名</param>
        public void MkDir(string strDirName)
        {
            if (!bConnected)
            {
                Connect();
            }
            SendCommand("MKD " + strDirName);
            if (iReplyCode != 257)
            {
                throw new IOException(strReply.Substring(4));
            }
        }
        /// <summary>
        /// 删除目录
        /// </summary>
        /// <param name="strDirName">目录名</param>
        public void RmDir(string strDirName)
        {
            if (!bConnected)
            {
                Connect();
            }
            SendCommand("RMD " + strDirName);
            if (iReplyCode != 250)
            {
                throw new IOException(strReply.Substring(4));
            }
        }......................
      一次贴不下全部的代码

Answer 1

有一个WebRequestMethods.Ftp.ListDirectory;