AsyncDownloadMethodWithCancellation.cs

using System;
using System.Net;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;

namespace test
{
    static class Program
    {

        public static void Main(string[] args)
        {
            var cts = new CancellationTokenSource();
            AsyncDownloadAndWrite(cts.Token);

            while (true)
            {
                ConsoleKeyInfo keyInfo = Console.ReadKey();
                if (keyInfo.Key == ConsoleKey.Backspace)
                {
                    cts.Cancel();
                    break;
                }
            }

            Console.ReadKey();
        }

        public static async Task AsyncDownloadAndWrite(CancellationToken token)
        {
            var client = new WebClient();

            TextProgressBar progressBar = new TextProgressBar(client);
            progressBar.StartDrawing();

            try
            {
                Console.WriteLine(await DownloadAsync(client, new Uri("http://ftp.byfly.by/test/100mb.txt"), token));
            }
            catch (TaskCanceledException exception)
            {
                Console.WriteLine(exception.Message);
            }
            catch (Exception exception)
            {
                Console.WriteLine(exception.Message);
                throw;
            }
        }


        public static async Task<string> DownloadAsync(WebClient client, Uri uri, CancellationToken token)
        {
            var taskCompletionSource = new TaskCompletionSource<string>();

            client.DownloadStringCompleted += SetResultAction;

            void SetResultAction(object sender, DownloadStringCompletedEventArgs data)
            {
                if (data.Cancelled)
                {
                    taskCompletionSource.SetCanceled();
                }
                else if (data.Error != null)
                {
                    taskCompletionSource.SetException(data.Error);
                }
                else
                {
                    taskCompletionSource.SetResult(data.Result);
                }
                client.DownloadStringCompleted -= SetResultAction;


            }


            using (token.Register(client.CancelAsync))
            {
                client.DownloadStringAsync(uri);

                return await taskCompletionSource.Task;
            }
        }
    }

    class TextProgressBar
    {
        private readonly object _synchronizationObject;
        private readonly WebClient _client;

        public TextProgressBar(WebClient client)
        {
            _client = client;
            Console.CursorVisible = false;
            _synchronizationObject = new object();
        }

        public void StartDrawing()
        {
            _client.DownloadProgressChanged += (sender, eventArgs) => Draw(eventArgs.BytesReceived, eventArgs.TotalBytesToReceive);

        }

        private void Draw(long progress, long total)
        {
            lock (_synchronizationObject)
            {
                Console.CursorLeft = 0;
                Console.Write("[");
                Console.CursorLeft = 32;
                Console.Write("]");
                Console.CursorLeft = 1;
                var oneChunk = 30.0f / total;

                var position = 1;
                for (var i = 0; i < oneChunk * progress; i++)
                {
                    Console.CursorLeft = position++;
                    Console.Write("#");
                }

                for (var i = position; i <= 31; i++)
                {
                    Console.CursorLeft = position++;
                    Console.Write(".");
                }
            }
        }
    }
}