C＃FTP下载文件出现远程服务器返回错误: (500) 语法错误，无法识别命令

布满荆棘的人生 2022-01-31 07:19 449阅读 0赞

如果下载多个文件的时候，有时候莫名其妙的出现500服务器错误，很有可能是没有设置KeepAlive 属性导致的。

出现应用程序未处理的异常：2015/1/6 11:40:56  
异常类型：WebException  
异常消息：远程服务器返回错误: (500) 语法错误，无法识别命令。

参考：[http://www.cnblogs.com/webabcd/archive/2007/01/21/626242.html][http_www.cnblogs.com_webabcd_archive_2007_01_21_626242.html]

KeepAlive - 指定连接是应该关闭还是在请求完成之后关闭，默认为true

/// <summary>
            /// FTP下载文件（带进度条）
            /// </summary>
            /// <param name="filename"></param>
            public void DownloadFile(string filename)
            {
                float percent = 0;
                string filePathName = string.Empty;
                string url = string.Empty;
                filePathName = Path.Combine(Application.StartupPath, filename);
                string dirPath = GetDirPath(filePathName);
                if (!Directory.Exists(dirPath))
                    Directory.CreateDirectory(dirPath);
                //=>替换文件目录中的路径为网络路径
                filename = filename.Replace("\\", "/");
                url = "ftp://" + clientUpdateInfo.UpdateFTPIP + "/" + clientUpdateInfo.UpdatePath + "/" + filename;
                var reqFtp = (FtpWebRequest)FtpWebRequest.Create(new Uri(url));
                reqFtp.Method = WebRequestMethods.Ftp.DownloadFile;
                reqFtp.UseBinary = true;
                reqFtp.KeepAlive = false;//一定要设置此属性，否则一次性下载多个文件的时候，会出现异常。
                reqFtp.Credentials = new NetworkCredential(clientUpdateInfo.FtpUserName, clientUpdateInfo.FtpUserPwd);
                var response = (FtpWebResponse)reqFtp.GetResponse();
                long totalBytes = response.ContentLength;
                if (prog != null)
                {
                    this.BeginInvoke(new MethodInvoker(delegate()
                    {
                        prog.Maximum = (int)totalBytes;
                    }));
                }
                Stream st = response.GetResponseStream();
                var so = new FileStream(filePathName, FileMode.Create);
                long totalDownloadedByte = 0;
                byte[] by = new byte[1024];
                int osize = st.Read(by, 0, (int)by.Length);
                while (osize > 0)
                {
                    totalDownloadedByte = osize + totalDownloadedByte;
                    so.Write(by, 0, osize);
                    if (prog != null)
                    {
                        this.BeginInvoke(new MethodInvoker(delegate()
                        {
                            prog.Value = (int)totalDownloadedByte;
                        }));
    
                    }
                    osize = st.Read(by, 0, (int)by.Length);
                    percent = (float)totalDownloadedByte * 1.0f / (float)totalBytes * 100;
                    Application.DoEvents();
                    this.BeginInvoke(new MethodInvoker(delegate()
                    {
                        lbDownInfo.Text = "正在下载" + filename + ",下载进度为:" + Math.Round(percent, 2) + "%";
                        lbDownInfo.Refresh();
                    }));
                    Application.DoEvents();
                }
                so.Close();
                st.Close();
                response.Close();
            }
    
            private void FtpDownload(string filename)
            {
                string filePathName = string.Empty;
                string url = string.Empty;
                filePathName = Path.Combine(Application.StartupPath, filename);
                string dirPath = GetDirPath(filePathName);
                if (!Directory.Exists(dirPath))
                    Directory.CreateDirectory(dirPath);
                //=>替换文件目录中的路径为网络路径
                filename = filename.Replace("\\", "/");
                url = "ftp://" + clientUpdateInfo.UpdateFTPIP + "/" + clientUpdateInfo.UpdatePath + "/" + filename;
                FtpWebRequest reqFTP;
                this.BeginInvoke(new MethodInvoker(delegate()
                {
                    this.lbDownInfo.Text = "开始下载中...";
                }));
                FileStream outputStream = new FileStream(filePathName, FileMode.Create);
                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(url));
                reqFTP.Credentials = new NetworkCredential(clientUpdateInfo.FtpUserName, clientUpdateInfo.FtpUserPwd);
                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
                reqFTP.UseBinary = true;
                reqFTP.KeepAlive = false;
    
                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();
                Stream ftpStream = response.GetResponseStream();
                int bufferSize = 1024;
                int readCount;
                byte[] buffer = new byte[bufferSize];
                readCount = ftpStream.Read(buffer, 0, bufferSize);
                //FTP上文件的大小
                int allbye = GetFtpFileSize(filename);// (int)response.ContentLength;
                int startbye = 0;
                this.BeginInvoke(new MethodInvoker(delegate()
                  {
                      this.prog.Maximum = allbye;
                      this.prog.Minimum = 0;
                      this.prog.Visible = true;
                      this.lbDownInfo.Visible = true;
                  }));
                while (readCount > 0)
                {
                    outputStream.Write(buffer, 0, readCount);
                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                    startbye += readCount;
                    this.BeginInvoke(new MethodInvoker(delegate()
                      {
                          this.lbDownInfo.Text = "已下载:" + (int)(startbye / 1024) + "KB/" + "总长度:"
                                                + (int)(allbye / 1024) + "KB" + " " + " 文件名:" + filename;
                          prog.Value = startbye;
                          this.lbDownInfo.Refresh();
                      }));
                    Application.DoEvents();
                    Thread.Sleep(5);
                }
                this.BeginInvoke(new MethodInvoker(delegate()
                {
                    this.prog.Visible = false;
                    this.lbDownInfo.Text = "下载成功!";
                }));
                ftpStream.Close();
                outputStream.Close();
                response.Close();
            }

[http_www.cnblogs.com_webabcd_archive_2007_01_21_626242.html]: http://www.cnblogs.com/webabcd/archive/2007/01/21/626242.html