如何使用 C# 中的 ftpwebrequest 从 FTP 服务器下载非常大的文件~50 GB

问题描述

我尝试使用 FtpWebRequest 从 FTP 服务器分块下载文件并将这些块合并到原始文件。该过程适用于 4GB 或更低的文件，但是当对 8GB 或 9GB 的文件尝试相同的过程时，我收到错误

这是我得到的错误

这是我制定的示例代码

private static long limitSize = Convert.ToInt64(ConfigurationManager.AppSettings["LimitSize"]);

public static void DownloadFromFTP()
    {
        var guid = Guid.NewGuid().ToString();

        var path = $"{System.Environment.CurrentDirectory}/UploadedFiles/{guid}";

        try
        {

            string strFilePath = ConfigurationManager.AppSettings["FilePath"];
            NetworkCredential credentials = new NetworkCredential(ConfigurationManager.AppSettings["UserName"],ConfigurationManager.AppSettings["Password"]);
            Console.WriteLine("Starting...");
            string name = ConfigurationManager.AppSettings["FileName"];
            var strFolderPath = ConfigurationManager.AppSettings["Key"] + name;
            FtpWebRequest sizeRequest = (FtpWebRequest)WebRequest.Create(strFilePath);
            sizeRequest.KeepAlive = false;
            sizeRequest.Credentials = credentials;
            sizeRequest.Method = WebRequestMethods.Ftp.GetFileSize;
            long size = sizeRequest.GetResponse().ContentLength;
            Console.WriteLine($"File has {size} bytes");

            double filesizecheck = Convert.Todouble(size) / Convert.Todouble(limitSize);
            int chunks = Convert.ToInt32(Math.Ceiling(filesizecheck));
            long chunkLength = size / chunks;

            List<Task> tasks = new List<Task>();


            if (!System.IO.Directory.Exists(path))
            {
                System.IO.Directory.CreateDirectory(path);
            }
            var filepath = $"{path}/{name}";


            for (int chunk = 0; chunk < chunks; chunk++)
            {
                int i = chunk;
                tasks.Add(Task.Run(() =>
                {
                    try
                    {
                        FtpWebRequest request = (FtpWebRequest)WebRequest.Create(strFilePath);
                        request.Credentials = credentials;
                        request.Method = WebRequestMethods.Ftp.DownloadFile;
                        request.UseBinary = true;
                        request.UsePassive = true;
                        request.KeepAlive = false;
                        request.ContentOffset = chunkLength * i;
                        long toread =
                            (i < chunks - 1) ? chunkLength : size - request.ContentOffset;
                        Console.WriteLine(
                            $"Downloading chunk {i + 1}/{chunks} with {toread} bytes ...");

                        using (Stream ftpStream = request.GetResponse().GetResponseStream())
                        using (Stream fileStream = File.Create(filepath + "." + i))
                        {
                            var bufferSize = Convert.ToInt32(ConfigurationManager.AppSettings["BufferSize"]);
                            byte[] buffer = new byte[bufferSize];
                            int read;
                            while (((read = (int)Math.Min(buffer.Length,toread)) > 0) &&
                                   ((read = ftpStream.Read(buffer,read)) > 0))
                            {
                                fileStream.Write(buffer,read);
                                toread -= read;
                            }
                        }
                        Console.WriteLine($"Downloaded chunk {i + 1}/{chunks}");
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine($"Exception: {ex}");
                        Console.ReadKey();
                    }
                }));
            }

            Console.WriteLine("Started all chunks downloads,waiting for them to complete...");
            Task.WaitAll(tasks.ToArray());
            CombineMultipleFilesIntoSingleFile(path,filepath);

            var result = UploadToS3(filepath,strFolderPath,size,path).Result;

            Console.WriteLine("Done");
            Console.ReadKey();

        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception " + ex.Message);
            DeleteFiles(path);
            Console.ReadKey();
        }
        Console.ReadKey();
        Console.ReadKey();
    }

这里是合并文件的方法

private static void CombineMultipleFilesIntoSingleFile(string inputDirectoryPath,string outputFilePath)
    {
        string[] inputFilePaths = Directory.GetFiles(inputDirectoryPath);
        Console.WriteLine("Number of files: {0}.",inputFilePaths.Length);
        using (var outputStream = File.Create(outputFilePath))
        {
            foreach (var inputFilePath in inputFilePaths)
            {
                using (var inputStream = File.OpenRead(inputFilePath))
                {
                    // Buffer size can be passed as the second argument.
                    inputStream.copyTo(outputStream);
                }
                Console.WriteLine("The file {0} has been processed.",inputFilePath);
            }
        }
    }

应用配置设置

    <add key="LimitSize" value="10000000"/>
    <add key="BufferSize" value="10240"/>

解决方法

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