.net 4.0 download async

gistfile1.txt

using System;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Calibration {
    public static class Server {
        public delegate void ProgressDelegate(int percents, long bytesReceived, long totalBytesToReceive);

        public static Task<string> DownloadFileAsync(string path, string saveFilePath, ProgressDelegate onProgress = null)
        {
            return DownloadAsync((webClient) =>
            {
                TaskCompletionSource<string> tcs = new TaskCompletionSource<string>(path);

                webClient.DownloadFileCompleted += (sender, e) =>
                {
                    if (e.Error != null)
                        tcs.TrySetException(e.Error);
                    else if (e.Cancelled)
                        tcs.TrySetCanceled();
                    else
                        tcs.TrySetResult(saveFilePath);
                };

                webClient.DownloadFileAsync(new Uri(path), saveFilePath);

                return tcs.Task;

            }, onProgress);
        }

        public static Task<byte[]> DownloadDataAsync(string path, ProgressDelegate onProgress = null)
        {
            return DownloadAsync((webClient) =>
            {
                TaskCompletionSource<byte[]> tcs = new TaskCompletionSource<byte[]>(path);

                webClient.DownloadDataCompleted += (sender, e) =>
                {
                    if (e.Error != null)
                        tcs.TrySetException(e.Error);
                    else if (e.Cancelled)
                        tcs.TrySetCanceled();
                    else
                        tcs.TrySetResult(e.Result);
                };

                webClient.DownloadDataAsync(new Uri(path));

                return tcs.Task;
            }, onProgress);
        }

        public static Task<string> DownloadStringAsync(string path, ProgressDelegate onProgress = null)
        {
            return DownloadAsync((webClient) =>
            {
                TaskCompletionSource<string> tcs = new TaskCompletionSource<string>(path);

                webClient.DownloadStringCompleted += (sender, e) =>
                {
                    if (e.Error != null)
                        tcs.TrySetException(e.Error);
                    else if (e.Cancelled)
                        tcs.TrySetCanceled();
                    else
                        tcs.TrySetResult(e.Result);
                };

                webClient.DownloadStringAsync(new Uri(path));

                return tcs.Task;

            }, onProgress);
        }

        private static Task<T> DownloadAsync<T>(Func<WebClient, Task<T>> downloadAction, ProgressDelegate onProgress = null)
        {
            using (var webClient = new WebClient())
            {
                if (onProgress != null)
                {
                    webClient.DownloadProgressChanged += (sender, e) =>
                    {
                        SynchronizationContext.Current.Post((state) =>
                        {
                            onProgress.Invoke(e.ProgressPercentage, e.BytesReceived, e.TotalBytesToReceive);
                        }, null);
                    };
                }
                webClient.Encoding = Encoding.UTF8;
                return downloadAction(webClient);
            }
        }
    }
}