[#8] Add auto update checker

Elwig/Helpers/StreamExtensions.cs

@@ -0,0 +1,25 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Elwig.Helpers {
+    public static class StreamExtensions {
+        public static async Task CopyToAsync(this Stream source, Stream destination, int bufferSize, IProgress<long>? progress = null, CancellationToken cancellationToken = default) {
+            ArgumentNullException.ThrowIfNull(source);
+            if (!source.CanRead) throw new ArgumentException("Has to be readable", nameof(source));
+            ArgumentNullException.ThrowIfNull(destination);
+            if (!destination.CanWrite) throw new ArgumentException("Has to be writable", nameof(destination));
+            ArgumentOutOfRangeException.ThrowIfNegative(bufferSize);
+
+            var buffer = new byte[bufferSize];
+            long totalBytesRead = 0;
+            int bytesRead;
+            while ((bytesRead = await source.ReadAsync(buffer, cancellationToken).ConfigureAwait(false)) != 0) {
+                await destination.WriteAsync(buffer.AsMemory(0, bytesRead), cancellationToken).ConfigureAwait(false);
+                totalBytesRead += bytesRead;
+                progress?.Report(totalBytesRead);
+            }
+        }
+    }
+}