断开连接时如何使用自动恢复下载FTP文件 [英] How to download FTP files with automatic resume in case of disconnect

问题描述

我可以下载FTP文件，但是下载代码没有简历功能，也没有多部分文件下载.因为文件大于500 MB，所以我无法连续下载它们，因为连接已关闭并且从头开始下载.如果断开连接，我希望我的代码恢复工作.

I can download FTP files, but the download code does not have a resume facility and multi part files download. Because there are file larger than 500 MB, I can't download them continuously, because the connection gets closed and it starts download from beginning. I wanted my code a resume facility if it gets disconnected.

我正在使用的代码是:

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);
    }
}

推荐答案

在开始下载之前，请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 FtpWebRequest 对象的> ContentOffset 成员.但是，FTP服务器可能不支持此功能.

Before you start downloading check for the existence of the file on the local filesystem. If it exists, then get the size and use that for the ContentOffset member of the FtpWebRequest object. This functionality may not be supported by the FTP server, though.

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