Question

我正在尝试使用以下代码从ftp服务器下载文件：

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);
                }

              }

创建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是当文件较大（例如150mb）时，该过程会挂起。由于某种原因，该程序不理解它已完成下载并仍尝试读取更多字节。

我更喜欢不包含使用外部库的答案。谢谢

Answer 1

我已使用您的代码成功下载了超过150MB的多个文件。正如其他人所建议的那样，您的FTP服务器可能存在问题。

Answer 2

我通过引入请求超时解决了我的问题 - 如果达到，则会使程序抛出WebException。在这种情况下，程序将从其剩余的位置恢复下载。这是我的代码：

这是一个方法，如果文件被下载则返回true，否则为

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：

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。

从FTP服务器下载大文件（~150MB）会挂起

2 个答案: