Adds a raw file mask for dynamic requests.

        Parameters
        ----------
        start : string
            The URL prefix that must be matched to perform this request.

        method_str : string
            The HTTP method for which to trigger the request.

        method : function(esrh, args)
            The function to execute to perform the request. The function takes
            two arguments. esrh is the QuickServerRequestHandler object that
            called the function. args is a map containing the arguments to the
            request (i.e., the rest of the URL as path segment array 'paths', a
            map of all query fields / flags 'query', the fragment string
            'fragment', and if the method was a POST the JSON form content
            'post'). The function must return a file object containing the
            response (preferably BytesIO). If the result is None no response
            body is sent. In this case make sure to send an appropriate error
            code.

def _add_file_mask(self, start, method_str, method):
        """Adds a raw file mask for dynamic requests.

        Parameters
        ----------
        start : string
            The URL prefix that must be matched to perform this request.

        method_str : string
            The HTTP method for which to trigger the request.

        method : function(esrh, args)
            The function to execute to perform the request. The function takes
            two arguments. esrh is the QuickServerRequestHandler object that
            called the function. args is a map containing the arguments to the
            request (i.e., the rest of the URL as path segment array 'paths', a
            map of all query fields / flags 'query', the fragment string
            'fragment', and if the method was a POST the JSON form content
            'post'). The function must return a file object containing the
            response (preferably BytesIO). If the result is None no response
            body is sent. In this case make sure to send an appropriate error
            code.
        """
        fm = self._f_mask.get(method_str, [])
        fm.append((start, method))
        fm.sort(key=lambda k: len(k[0]), reverse=True)
        self._f_mask[method_str] = fm
        self._f_argc[method_str] = None