how resume able file download in asp.net with c# -> best way (for large files too)

Question

see the below handler :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace FileExplorer
{
    /// 

        

Answer 1

As requested, here's a "cleaned up" version of the answer:

public static bool DownloadFileMethod(HttpContext httpContext, string filePath, long speed)
{
    // Many changes: mostly declare variables near use
    // Extracted duplicate references to HttpContext.Response and .Request
    // also duplicate reference to .HttpMethod

    // Removed try/catch blocks which hid any problems
    var response = httpContext.Response;
    var request = httpContext.Request;
    var method = request.HttpMethod.ToUpper();
    if (method != "GET" &&
        method != "HEAD")
    {
        response.StatusCode = 501;
        return false;
    }

    if (!File.Exists(filePath))
    {
        response.StatusCode = 404;
        return false;
    }

    // Stream implements IDisposable so should be in a using block
    using (var myFile = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        var fileLength = myFile.Length;
        if (fileLength > Int32.MaxValue)
        {
            response.StatusCode = 413;
            return false;
        }

        var lastUpdateTiemStr = File.GetLastWriteTimeUtc(filePath).ToString("r");
        var fileName = Path.GetFileName(filePath);
        var fileNameUrlEncoded = HttpUtility.UrlEncode(fileName, Encoding.UTF8);
        var eTag = fileNameUrlEncoded + lastUpdateTiemStr;

        var ifRange = request.Headers["If-Range"];
        if (ifRange != null && ifRange.Replace("\"", "") != eTag)
        {
            response.StatusCode = 412;
            return false;
        }

        long startBytes = 0;

        // Just guessing, but I bet you want startBytes calculated before
        // using to calculate content-length
        var rangeHeader = request.Headers["Range"];
        if (rangeHeader != null)
        {
            response.StatusCode = 206;
            var range = rangeHeader.Split(new[] {'=', '-'});
            startBytes = Convert.ToInt64(range[1]);
            if (startBytes < 0 || startBytes >= fileLength)
            {
                // TODO: Find correct status code
                response.StatusCode = (int) HttpStatusCode.BadRequest;
                response.StatusDescription =
                    string.Format("Invalid start of range: {0}", startBytes);
                return false;
            }
        }

        response.Clear();
        response.Buffer = false;
        response.AddHeader("Content-MD5", GetMD5Hash(filePath));
        response.AddHeader("Accept-Ranges", "bytes");
        response.AppendHeader("ETag", string.Format("\"{0}\"", eTag));
        response.AppendHeader("Last-Modified", lastUpdateTiemStr);
        response.ContentType = "application/octet-stream";
        response.AddHeader("Content-Disposition", "attachment;filename=" +
                                                    fileNameUrlEncoded.Replace("+", "%20"));
        var remaining = fileLength - startBytes;
        response.AddHeader("Content-Length", remaining.ToString());
        response.AddHeader("Connection", "Keep-Alive");
        response.ContentEncoding = Encoding.UTF8;

        if (startBytes > 0)
        {
            response.AddHeader("Content-Range",
                                string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
        }

        // BinaryReader implements IDisposable so should be in a using block
        using (var br = new BinaryReader(myFile))
        {
            br.BaseStream.Seek(startBytes, SeekOrigin.Begin);

            const int packSize = 1024*10; //read in block，every block 10K bytes
            var maxCount = (int) Math.Ceiling((remaining + 0.0)/packSize); //download in block
            for (var i = 0; i < maxCount && response.IsClientConnected; i++)
            {
                response.BinaryWrite(br.ReadBytes(packSize));
                response.Flush();

                // HACK: Unexplained sleep
                var sleep = (int) Math.Ceiling(1000.0*packSize/speed); //the number of millisecond
                if (sleep > 1) Thread.Sleep(sleep);
            }
        }
    }
    return true;
}