private string strHost, strPath, strUser, strPassword, strMessage;
    private int intPort, bytes;
    private Socket socket;
    private int intStatusNumber;
    private string strReply;
    Byte[] buffer = new Byte[1024];
    Encoding encoding = Encoding.Default;

   

    #region 基本构造函数
    /// <summary>
    /// 构造函数(默认端口21)
    /// </summary>
    /// <param name="strHost">主机IP</param>
    /// <param name="strUser">账号</param>
    /// <param name="strPassword">密码</param>
    public FTP(string strHost, string strUser, string strPassword)  : this(strHost, 21, strUser, strPassword)
    {
    }
    /// <summary>
    /// 构造函数
    /// </summary>
    /// <param name="strHost">主机IP</param>
    /// <param name="intPort">端口号</param>
    /// <param name="strUser">账号</param>
    /// <param name="strPassword">密码</param>
    public FTP(string strHost, int intPort, string strUser, string strPassword)
    {
        this.strHost = strHost;
        this.strPath = ".";
        this.strUser = strUser;
        this.strPassword = strPassword;
        this.intPort = intPort;
    }

    public void SetEncoding(Encoding encoding)
    {
        this.encoding = encoding;
    }
    public void SetEncoding(string strName)
    {
        this.encoding = Encoding.GetEncoding(strName);
    }
    public void SetEncoding(int encodingIndex)
    {
        this.encoding = Encoding.GetEncoding(encodingIndex);
    }
    public void Setbuffer(uint buff)
    {
        this.buffer = new byte[buff];
    }
    #endregion

    /// <summary>
    /// 得到一个目录下的List
    /// </summary>
    /// <param name="strName">目录名</param>
    /// <returns></returns>
    public string[] GetFileList(string strName)
    {
        Socket sk = CreateSocket();
        SetCommand("NLST " + strName);
        if (!(intStatusNumber == 150 || intStatusNumber == 125))
        {
            return null;
        }
        strMessage = string.Empty;
        while (true)
        {
            int bytes = sk.Receive(buffer, buffer.Length, 0);
            strMessage += encoding.GetString(buffer, 0, bytes);
            if (bytes < buffer.Length)
            {
                break;
            }
        }
        string[] strFileNames = strMessage.Split(new char[] { '\n' });
        sk.Close();
        ChangeValue();
        if (intStatusNumber != 226)
        {
            throw new IOException(strReply.Substring(4));
        }
        return strFileNames;
    }

    /// <summary>
    /// 得到文件大小
    /// </summary>
    /// <param name="fileName">文件路径</param>
    /// <returns>-1表示出现错误</returns>
    public int GetFileSize(string fileName)
    {
        try
        {
            SetCommand("SIZE " + fileName);
            int size = 0;
            if (intStatusNumber == 213)
            {
                size = int.Parse(strReply.Substring(4));
            }
            else
            {
                throw new IOException(strReply.Substring(4));
            }
            return size;
        }
        catch 
        {
            return -1;
        }
    }

    /// <summary>
    /// 登陆到FTP服务器
    /// </summary>
    public bool Login()
    {
        bool blLogin = false;
        socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        IPEndPoint ep = new IPEndPoint(IPAddress.Parse(strHost), intPort);
        try
        {
            socket.Connect(ep);
            ChangeValue();
            if (intStatusNumber != 220)
            {
                Close();
                throw new IOException(strReply.Substring(4));
            }
  
            SetCommand("USER " + strUser);

            if (!(intStatusNumber == 331 || intStatusNumber == 230))
            {
                CleanUP();
                throw new IOException(strReply.Substring(4));
            }

            if (intStatusNumber != 230)
            {
                SetCommand("PASS " + strPassword);
                if (!(intStatusNumber == 230 || intStatusNumber == 202))
                {
                    CleanUP();
                    throw new IOException(strReply.Substring(4));
                }
            }
            blLogin = true;
        }
        catch (Exception)
        {
            throw new IOException("Couldn't connect to remote server");
        }
        return blLogin;
    }
  
    /// <summary>
    /// 下载文件
    /// </summary>
    /// <param name="strRemoteName">远程地址</param>
    /// <param name="strLocalName">保存本地路径</param>
    public bool DownLoadFile(string strRemoteName, string strLocalName)
    {
        bool bl = true;
        FileStream stream = null;
        Socket sk = null;
        try
        {
            if (!File.Exists(strLocalName))
            {
                Stream st = File.Create(strLocalName);
                st.Close();
            }
            stream = new FileStream(strLocalName, FileMode.Open);
            sk = CreateSocket();
            SetCommand("RETR " + strRemoteName);
            if (!(intStatusNumber == 150 || intStatusNumber == 125))
            {
                throw new IOException(strReply.Substring(4));
            }
            while (true)
            {
                bytes = sk.Receive(buffer, buffer.Length, 0);
                stream.Write(buffer, 0, bytes);
                if (bytes <= 0)
                {
                    break;
                }
            }
            ChangeValue();
            if (!(intStatusNumber == 226 || intStatusNumber == 250))
            {
                throw new IOException(strReply.Substring(4));
            }
        }
        catch
        {
            bl = false;
        }
        finally
        {
            if (sk != null)
            {
                sk.Close();
            }
            if (stream != null)
            {
                stream.Close();
            }
        }
        return bl;
    }

    /// <summary>
    /// 上传文件
    /// </summary>
    /// <param name="fileName">文件名</param>
    /// <param name="strNewName">新的文件名如 abc
    /// 如果为空那么采用原来的文件名</param>
    public bool UPLoadFile(string fileName,string strNewName)
    {
        bool bl = true;
        Socket sk = CreateSocket();
        FileStream stream = null;
        try
        {
            if (strNewName.Length == 0)
            {
                SetCommand("STOR " + Path.GetFileName(fileName));
            }
            else
            {
                SetCommand("STOR " + strNewName + fileName.Substring(fileName.LastIndexOf(".")));
            }
            if (!(intStatusNumber == 125 || intStatusNumber == 150))
            {
                throw new IOException(strReply.Substring(4));
            }
             stream = new FileStream(fileName, FileMode.Open);
            while ((bytes = stream.Read(buffer, 0, buffer.Length)) > 0)
            {
                sk.Send(buffer, bytes, 0);
            }
            ChangeValue();
            if (!(intStatusNumber == 226 || intStatusNumber == 250))
            {
                throw new IOException(strReply.Substring(4));
            }
        }
        catch
        {
            bl = false;
        }
        finally
        {
            if (sk != null)
            {
                sk.Close();
            }
            if (stream != null)
            {
                stream.Close();
            }
        }

        return bl;
    }