gistfile1.txt

 if (!this.stream.CanSeek) 
            { 
                var tcs = new TaskCompletionSource<Stream>();
                var buffer = 
                    new MemoryStream((int)this.stream.Length); 
 
                this.stream.CopyTo(buffer, (source, destination, ex) => 
                { 
                    if (ex != null)
                    {
                      tcs.SetException(ex);
                    }
                    else
                    {
                      tcs.SetResult(destination);
                    }
                }); 
                var task = tcs.Task;
                // ^^ pull this out into a method that returns tcs.task

                task.Wait();
  
                if (task.IsFaulted)
                {
                   throw new InvalidOperationException("Unable to copy stream", task.Exception);
                }

                this.stream = task.Result.
            }