public IDisposable RegisterFileUploadHandler(string id, FileUploadHandlerDelegate handler)
        {
            FileUploadHandler fileUploadHandler =
                new FileUploadHandler(handler, () => _registeredInputFiles.TryRemove(id, out _));

            if (!_registeredInputFiles.TryAdd(id, fileUploadHandler))
            {
                throw new InvalidOperationException($"Id '{id}' is already registered");
            }

            return(fileUploadHandler);
        }
 public FileUploadHandler(FileUploadHandlerDelegate handler, Action disposeAction)
 {
     Handler       = handler;
     DisposeAction = disposeAction;
 }