def METHOD_NAME(self, environ, start_response):
    self.assertEqual(environ, self.environ)
    if self.serve_file:
        headers = {FileServerMiddleware.DIGEST_HEADER: self.digest}
        if self.provide_filename:
            headers[FileServerMiddleware.FILENAME_HEADER] = self.filename
        return Response(headers=headers, mimetype=self.mimetype)
    else:
        return Response(b"some other content", mimetype="text/plain")