code: def wrap_guess_content_type(func_, *args, **kwargs):
      
      assert isinstance(args[0], dict)
      if not args[0].get(CONTENTTYPE_FIELD, None):
          content = args[0].get(CONTENT_FIELD, b"")
          try:
              args[0][CONTENTTYPE_FIELD] = magic.from_buffer(content)
          except magic.MagicException:  # pragma: no cover
              args[0][CONTENTTYPE_FIELD] = MockMagic.DEFAULT_MAGIC
      return func_(*args, **kwargs)
docs: guesses the content type with libmagic if available
      :param func_:
      :param args:
      :param kwargs:
      :return: