从 FTP 服务器下载大文件(~150MB)挂起

问题描述

我正在尝试使用以下代码从 ftp 服务器下载文件:

I am trying to download files from ftp server with this code:

using (System.IO.FileStream fileStream = System.IO.File.OpenWrite(filePath))
              {

                byte[] buffer = new byte[4096];

                int bytesRead = responseStream.Read(buffer, 0, 4096);
                while (bytesRead > 0)
                {
                  fileStream.Write(buffer, 0, bytesRead);                      
                  bytesRead = responseStream.Read(buffer, 0, 4096);
                }

              }

responseStream的创建:

The creation of responseStream:

System.IO.Stream responseStream = GetFileAsStream(url, username, password, false);

public static System.IO.Stream GetFileAsStream(string ftpUrl, string username, string password, bool usePassive)
{
  System.Net.FtpWebRequest request = (System.Net.FtpWebRequest)System.Net.WebRequest.Create(ftpUrl);
  request.KeepAlive = false;
  request.ReadWriteTimeout = 120000;
  request.Timeout = -1;
  request.UsePassive = usePassive;

  request.Credentials = new System.Net.NetworkCredential(username, password);

  request.Method = System.Net.WebRequestMethods.Ftp.DownloadFile;

  System.IO.Stream fileResponseStream;


  System.Net.FtpWebResponse fileResponse = (System.Net.FtpWebResponse)request.GetResponse();



  fileResponseStream = fileResponse.GetResponseStream();

  return fileResponseStream;
}

它适用于较小的文件，但当文件较大(例如 150mb)时，进程会挂起.出于某种原因，程序不理解它已完成下载，并且仍在尝试读取更多字节.

It works fine with smaller files but when a file is bigger (e.g. 150mb) the process hangs. For some reason the program does not understand that it has completed the download and it still tries to read more bytes.

我更喜欢不包括使用外部库的答案.谢谢

I prefer answers which do not include using external libraries. Thank you

推荐答案

我通过引入请求超时解决了我的问题——如果达到，程序会抛出 WebException.在这种情况下，程序会从它离开的地方继续下载.这是我的代码:

I have solved my problem by introducing a request timeout- which, if reached, makes the program to throw a WebException. In that case, the program resumes the download from the place it left of. Here's my code :

这是一个方法的内部，如果文件被下载则返回 true，否则返回 false-

This is inside of a method which is returning true if the file is downloaded, false- otherwise

Digitalez.DirectoryUtil.EnsureDirectoryExists(relativePath);

        string filePath = System.IO.Path.Combine(relativePath, fileInfo.Name);
        long length = Digitalez.FtpUtil.GetFileLength(fileInfo.FullPath, userName, password, usePassive);
        long offset = 0;
        int retryCount = 10;
        int? readTimeout = 5 * 60 * 1000; //five minutes

        // if the file exists, do not download it
        if (System.IO.File.Exists(filePath))
        {
          return false;
        }

        while (retryCount > 0)
        {

          using (System.IO.Stream responseStream = Captator.Eifos.Net.FtpUtil.GetFileAsStream(fileInfo.FullPath, userName, password, usePassive, offset, requestTimeout: readTimeout != null ? readTimeout.Value : System.Threading.Timeout.Infinite))
          {

            using (System.IO.FileStream fileStream = new System.IO.FileStream(filePath, System.IO.FileMode.Append))
            {
              byte[] buffer = new byte[4096];
              try
              {
                int bytesRead = responseStream.Read(buffer, 0, buffer.Length);

                while (bytesRead > 0)
                {
                  fileStream.Write(buffer, 0, bytesRead);

                  bytesRead = responseStream.Read(buffer, 0, buffer.Length);
                }

                return true;
              }
              catch (System.Net.WebException)
              {
                // Do nothing - consume this exception to force a new read of the rest of the file
              }
            }

            if (System.IO.File.Exists(filePath))
            {
              offset = new System.IO.FileInfo(filePath).Length;
            }
            else
            {
              offset = 0;
            }

            retryCount--;

            if (offset == length)
            {
              return true;
            }

          }
        }

Digitalez.FtpUtil:

Digitalez.FtpUtil:

public static System.IO.Stream GetFileAsStream(string ftpUrl, string username, string password, bool usePassive, long offset, int requestTimeout)
{
  System.Net.FtpWebRequest request = (System.Net.FtpWebRequest)System.Net.WebRequest.Create(ftpUrl);

  request.KeepAlive = false;
  request.ReadWriteTimeout = requestTimeout;
  request.Timeout = requestTimeout;
  request.ContentOffset = offset;
  request.UsePassive = usePassive;
  request.UseBinary = true;

  request.Credentials = new System.Net.NetworkCredential(username, password);

  request.Method = System.Net.WebRequestMethods.Ftp.DownloadFile;

  System.IO.Stream fileResponseStream;

  System.Net.FtpWebResponse fileResponse = (System.Net.FtpWebResponse)request.GetResponse();

  fileResponseStream = fileResponse.GetResponseStream();

  return fileResponseStream;
}

public static long GetFileLength(string ftpUrl, string username, string password, bool usePassive)
{
  System.Net.FtpWebRequest request = (System.Net.FtpWebRequest)System.Net.WebRequest.Create(ftpUrl);

  request.KeepAlive = false;
  request.UsePassive = usePassive;


  request.Credentials = new System.Net.NetworkCredential(username, password);
  request.Method = System.Net.WebRequestMethods.Ftp.GetFileSize;

  System.Net.FtpWebResponse lengthResponse = (System.Net.FtpWebResponse)request.GetResponse();
  long length = lengthResponse.ContentLength;
  lengthResponse.Close();
  return length;

}

我没有尝试过其他服务器，但这确实可以解决问题.

I haven't tried other servers but this certainly does the trick.

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