Adding pause and continue ability in my downloader

Question

I am creating a downloader in C#. I am using WebClient class. To pause downloading on a button click I could just think of using Thread. So when I created thread and attached it with my file downloading as below

WebClient web = new WebLCient();
Thread dwnd_thread = new Thread(Program.web.DownloadFileAsync(new Uri(Program.src), Program.dest));

it is giving me following errors: "The best overloaded method match for 'System.Threading.Thread.Thread(System.Threading.ThreadStart)' has some invalid arguments" and "Argument '1': cannot convert from 'void' to 'System.Threading.ThreadStart'".

Then I thought if I pause my system main thread then it could block my whole process for that I used below line of code

System.Threading.Thread.Sleep(100);

but it is doing nothing at all. Can somebody tell me what could be a better approach for pause/downloading and how to use thread to pause my downloading process.

Answer 1

As there's no standard way of pause/resume a download request, you'll have to implement your own mechanism. Below is a block of code, containing an example of how such a mechanism could look. The class FileDownload takes 3 parameters:

• source - url to the file, to download.

• destination - where to save the file.

• chunkSize - how many bytes to read, before checking whether to pause or continue the download.

---

public class FileDownload
{
    private volatile bool _allowedToRun;
    private string _source;
    private string _destination;
    private int _chunkSize;

    private Lazy<int> _contentLength;

    public int BytesWritten { get; private set; }
    public int ContentLength { get { return _contentLength.Value; } }

    public bool Done { get { return ContentLength == BytesWritten; } }

    public FileDownload(string source, string destination, int chunkSize)
    {
        _allowedToRun = true;

        _source = source;
        _destination = destination;
        _chunkSize = chunkSize;
        _contentLength = new Lazy<int>(() => Convert.ToInt32(GetContentLength()));

        BytesWritten = 0;
    }

    private long GetContentLength()
    {
        var request = (HttpWebRequest)WebRequest.Create(_source);
        request.Method = "HEAD";

        using (var response = request.GetResponse())
            return response.ContentLength;
    }

    private async Task Start(int range)
    {
        if (!_allowedToRun)
            throw new InvalidOperationException();

        var request = (HttpWebRequest)WebRequest.Create(_source);
        request.Method = "GET";
        request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)";
        request.AddRange(range);

        using (var response = await request.GetResponseAsync())
        {
            using (var responseStream = response.GetResponseStream())
            {
                using (var fs = new FileStream(_destination, FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
                {
                    while (_allowedToRun)
                    {
                        var buffer = new byte[_chunkSize];
                        var bytesRead = await responseStream.ReadAsync(buffer, 0, buffer.Length);

                        if (bytesRead == 0) break;

                        await fs.WriteAsync(buffer, 0, bytesRead);
                        BytesWritten += bytesRead;
                    }

                    await fs.FlushAsync();
                }
            }
        }
    }

    public Task Start()
    {
        _allowedToRun = true;
        return Start(BytesWritten);
    }

    public void Pause()
    {
        _allowedToRun = false;
    }
}

Usage:

static void Main(string[] args)
{
    var fw = new FileDownload("http://download.microsoft.com/download/E/E/2/EE2D29A1-2D5C-463C-B7F1-40E4170F5E2C/KinectSDK-v1.0-Setup.exe", @"D:\KinetSDK.exe", 5120);

    // Display progress...
    Task.Factory.StartNew(() =>
    {
        while (!fw.Done)
        {
            Console.SetCursorPosition(0, Console.CursorTop);
            Console.Write(string.Format("ContentLength: {0} | BytesWritten: {1}", fw.ContentLength, fw.BytesWritten));
        }
    });

    // Start the download...
    fw.Start();

    // Simulate pause...
    Thread.Sleep(500);
    fw.Pause();
    Thread.Sleep(2000);

    // Start the download from where we left, and when done print to console.
    fw.Start().ContinueWith(t => Console.WriteLine("Done"));

    Console.ReadKey();
}