Downloading files is a common scenario, specially in connected apps like you can find in Windows 8.

When these files are hosted in Web server, downloads is really easy to perform using a WebRequest (C#) or XHR (XmlHttpRequest, in JS). But when the files are located on FTP server, it’s a bit more complicated so we have to find a way to be able to download files.

The answer to this problem is to use the BackgroundDownloader class:

var file = await KnownFolders.DocumentsLibrary.CreateFileAsync("Yoda.jpg", CreationCollisionOption.ReplaceExisting);

var pc = new PasswordCredential();
pc.UserName = "freebox";
pc.Password = "XXXXX";

var downloader = new BackgroundDownloader();
downloader.ServerCredential = pc;
var downloadOperation = downloader.CreateDownload(new Uri("ftp://hd1.freebox.fr/Disque dur/Yoda.jpg"), file);

var progressCallback = new Progress<DownloadOperation>(op =>
{
    if (op.Progress.TotalBytesToReceive > 0)
    {
        Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
        {
            this._progressPercent = op.Progress.BytesReceived * 100 / op.Progress.TotalBytesToReceive;
        });

        }
});

await downloadOperation.StartAsync().AsTask(progressCallback);

var response = downloadOperation.GetResponseInformation();

Unfortunately, if you try to execute the following code, you’ll encounter this error:

Indeed, there is actually a bug when you try to specify the ServerCredential property of the BackgroundDownloader (thanks to Katrien De Graeve, @katriendg for pointing me this). The workaround is to set the username/password in the Uri:

var file = await KnownFolders.DocumentsLibrary.CreateFileAsync("Yoda.jpg", CreationCollisionOption.ReplaceExisting);

var pc = new PasswordCredential();
pc.UserName = "freebox";
pc.Password = "XXXXX";

var downloader = new BackgroundDownloader();
//downloader.ServerCredential = pc;
var downloadOperation = downloader.CreateDownload(new Uri("ftp://freebox:XXXXX@hd1.freebox.fr/Disque dur/Yoda.jpg"), file);

var progressCallback = new Progress<DownloadOperation>(op =>
{
    if (op.Progress.TotalBytesToReceive > 0)
    {
        Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
        {
            this._progressPercent = op.Progress.BytesReceived * 100 / op.Progress.TotalBytesToReceive;
        });

    }
});

await downloadOperation.StartAsync().AsTask(progressCallback);

var response = downloadOperation.GetResponseInformation();

Using this code, you’ll be able to download the file successfully !

Note that, to use this code, you need to set the following capacities:

Happy coding!