如何在附件管理模块中增加对FTP 上传和预览的支持？

// create an FTP clientFtpClient client = new FtpClient("123.123.123.123");// if you don't specify login credentials, we use the "anonymous" user accountclient.Credentials = new NetworkCredential("david", "pass123");// begin connecting to the serverclient.Connect();// get a list of files and directories in the "/htdocs" folderforeach (FtpListItem item in client.GetListing("/htdocs")) {    // if this is a fileif (item.Type == FtpFileSystemObjectType.File){        // get the file sizelong size = client.GetFileSize(item.FullName);
        
    }    // get modified date/time of the file or folderDateTime time = client.GetModifiedTime(item.FullName);    // calculate a hash for the file on the server side (default algorithm)FtpHash hash = client.GetHash(item.FullName);
    
}// upload a fileclient.UploadFile(@"C:\MyVideo.mp4", "/htdocs/big.txt");// rename the uploaded fileclient.Rename("/htdocs/big.txt", "/htdocs/big2.txt");// download the file againclient.DownloadFile(@"C:\MyVideo_2.mp4", "/htdocs/big2.txt");// delete the fileclient.DeleteFile("/htdocs/big2.txt");// delete a folder recursivelyclient.DeleteDirectory("/htdocs/extras/");// check if a file existsif (client.FileExists("/htdocs/big2.txt")){ }// check if a folder existsif (client.DirectoryExists("/htdocs/extras/")){ }// upload a file and retry 3 times before giving upclient.RetryAttempts = 3;
client.UploadFile(@"C:\MyVideo.mp4", "/htdocs/big.txt", FtpExists.Overwrite, false, FtpVerify.Retry);// disconnect! good bye!client.Disconnect();

    /// 
/// FTP配置信息/// 
    [DataContract]
    [Serializable]public class FTPInfo
    {/// 
/// 默认构造函数/// 
public FTPInfo()
        {

        }/// 
/// 参数化构造函数/// 
/// /// /// public FTPInfo(string server, string user, string password, string baseUrl)
        {this.Server = server;this.User = user;this.Password = password;this.BaseUrl = baseUrl;
        }/// 
/// FTP服务地址/// 
        [DataMember]public string Server { get; set; }/// 
/// FTP用户名/// 
        [DataMember]public string User { get; set; }/// 
/// FTP密码/// 
        [DataMember]public string Password { get; set; }/// 
/// FTP的基础路径，如可以指定为IIS的路径：:8000 ,方便下载打开/// 
        [DataMember]public string BaseUrl { get; set; }
    }

        /// 
/// 获取配置的FTP配置参数/// 
/// private FTPInfo GetFTPConfig()
        {var ftp_server = config.AppConfigGet("ftp_server");var ftp_user = config.AppConfigGet("ftp_user");var ftp_pass = config.AppConfigGet("ftp_password");var ftp_baseurl = config.AppConfigGet("ftp_baseurl");return new FTPInfo(ftp_server, ftp_user, ftp_pass, ftp_baseurl);
        }

//使用FluentFTP操作FTP文件FtpClient client = new FtpClient(ftpInfo.Server, ftpInfo.User, ftpInfo.Password);

//确定日期时间目录（格式：yyyy-MM），不存在则创建string savePath = string.Format("/{0}-{1:D2}/{2}", DateTime.Now.Year, DateTime.Now.Month, category);bool isExistDir = client.DirectoryExists(savePath);if(!isExistDir)
{
    client.CreateDirectory(savePath);
}

//使用FTP上传文件//避免文件重复，使用GUID命名var ext = FileUtil.GetExtension(info.FileName);var newFileName = string.Format("{0}{1}", Guid.NewGuid().ToString(), ext);//FileUtil.GetFileName(file);savePath = savePath.UriCombine(newFileName);bool uploaded = client.Upload(info.FileData, savePath, FtpExists.Overwrite, true);