如何在断开连接的情况下自动恢复下载 FTP 文件答案

【问题标题】：How to download FTP files with automatic resume in case of disconnect如何在断开连接的情况下自动恢复下载 FTP 文件
【发布时间】：2011-09-13 22:33:06
【问题描述】：

我可以下载 FTP 文件，但下载代码没有恢复功能和多部分文件下载。因为有大于 500 MB 的文件，我不能连续下载它们，因为连接被关闭，它从头开始下载。如果我的代码断开连接，我希望我的代码成为恢复工具。

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);
    }
}

【问题讨论】：

标签： c# .net ftp ftpwebrequest

【解决方案1】：

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。不过，FTP 服务器可能不支持此功能。

【讨论】：

【解决方案2】：

使用FtpWebRequest 恢复FTP 下载的本机实现：

bool resume = false;
do
{
    try
    {
        FileMode mode = resume ? FileMode.Append : FileMode.Create;
        resume = false;
        using (Stream fileStream = File.Open(@"C:\local\path\file.dat", mode))
        {
            var url = "ftp://ftp.example.com/remote/path/file.dat";
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create(url);
            request.Credentials = new NetworkCredential("username", "password");
            request.Method = WebRequestMethods.Ftp.DownloadFile;
            request.ContentOffset = fileStream.Position;
            using (Stream ftpStream = request.GetResponse().GetResponseStream())
            {
                ftpStream.CopyTo(fileStream);
            }
        }
    }
    catch (WebException)
    {
        resume = true;
    }
}
while (resume);

或者使用可以自动恢复传输的 FTP 库。

例如WinSCP .NET assembly 可以。有了它，可恢复的下载就变得如此简单：

// Setup session options
var sessionOptions = new WinSCP.SessionOptions
{
    Protocol = Protocol.Ftp,
    HostName = "ftp.example.com",
    UserName = "user",
    Password = "mypassword"
};

using (var session = new Session())
{
    // Connect
    session.Open(sessionOptions);

    // Resumable download
    session.GetFileToDirectory("/home/user/file.zip", @"C:\path");
}

（我是 WinSCP 的作者）

【讨论】：