System.IO.MemoryStream.CopyToAsyncImpl C# (CSharp) Method

        private async Task CopyToAsyncImpl(Stream destination, int bufferSize, CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();

            // Avoid copying data from this buffer into a temp buffer:
            //   (require that InternalEmulateRead does not throw,
            //    otherwise it needs to be wrapped into try-catch-Task.FromException like memStrDest.Write below)

            int pos = _position;
            int n = InternalEmulateRead(_length - _position);

            // If destination is not a memory stream, write there asynchronously:
            MemoryStream memStrDest = destination as MemoryStream;
            if (memStrDest == null)
            {
                await destination.WriteAsync(_buffer, pos, n, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                memStrDest.Write(_buffer, pos, n);
            }
        }