c# - 如何在断开连接的情况下自动恢复下载 FTP 文件

Question

我可以下载 FTP 文件，但下载代码没有恢复工具和多部分文件下载。因为有大于 500 MB 的文件，我无法连续下载它们，因为连接关闭并从头开始下载。如果它断开连接，我希望我的代码有一个恢复工具。

我使用的代码是:

public string[] GetFileList()
{
    string[] downloadFiles;
    StringBuilder result = new StringBuilder();
    FtpWebRequest reqFTP;
    try
    {
        reqFTP = (FtpWebRequest)FtpWebRequest.Create(
            new Uri("ftp://" + ftpServerIP + "/"));
        reqFTP.UseBinary = true;
        reqFTP.Credentials = new NetworkCredential(ftpUserID, ftpPassword);
        reqFTP.Method = WebRequestMethods.Ftp.ListDirectory;
        WebResponse response = reqFTP.GetResponse();
        StreamReader reader = new StreamReader(response.GetResponseStream());
        //MessageBox.Show(reader.ReadToEnd());
        string line = reader.ReadLine();
        while (line != null)
        {
            result.Append(line);
            result.Append("\n");
            line = reader.ReadLine();
        }
        result.Remove(result.ToString().LastIndexOf('\n'), 1);
        reader.Close();
        response.Close();
        //MessageBox.Show(response.StatusDescription);
        return result.ToString().Split('\n');
    }
    catch (Exception ex)
    {
        System.Windows.Forms.MessageBox.Show(ex.Message);
        downloadFiles = null;
        return downloadFiles;
    }
}

private void Download(string filePath, string fileName)
{
    FtpWebRequest reqFTP;
    try
    {
        //filePath = <<The full path where the file is to be created.>>, 
        //fileName = <<Name of the file to be created
        //             (Need not be the name of the file on FTP server).>>
        FileStream outputStream =
            new FileStream(filePath + "\\" + fileName, FileMode.Create);

        reqFTP = (FtpWebRequest)FtpWebRequest.Create(
            new Uri("ftp://" + ftpServerIP + "/" + fileName));
        reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
        reqFTP.UseBinary = true;
        reqFTP.Credentials = new NetworkCredential(ftpUserID, ftpPassword);
        FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();
        Stream ftpStream = response.GetResponseStream();
        long cl = response.ContentLength;
        int bufferSize = 2048;
        int readCount;
        byte[] buffer = new byte[bufferSize];

        readCount = ftpStream.Read(buffer, 0, bufferSize);
        while (readCount > 0)
        {
            outputStream.Write(buffer, 0, readCount);
            readCount = ftpStream.Read(buffer, 0, bufferSize);
        }

        ftpStream.Close();
        outputStream.Close();
        response.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Answer 1

在开始下载之前，检查本地文件系统上是否存在该文件。如果存在，则获取大小并将其用于 ContentOffset FtpWebRequest 对象的成员。不过，FTP 服务器可能不支持此功能。