def _validate_fetch(self):
        """Validate the fetch.txt file

        Raises `BagError` for errors and otherwise returns no value
        """
        for url, file_size, filename in self.fetch_entries():
            # fetch_entries will raise a BagError for unsafe filenames
            # so at this point we will check only that the URL is minimally
            # well formed:
            parsed_url = urlparse(url)

            # only check for a scheme component since per the spec the URL field is actually a URI per
            # RFC3986 (https://tools.ietf.org/html/rfc3986)
            if not all(parsed_url.scheme):
                raise BagError(_('Malformed URL in fetch.txt: %s') % url)
Validate the fetch.txt file

        Raises `BagError` for errors and otherwise returns no value