public static function search_contacts_returns() {
        return new external_multiple_structure(
            new external_single_structure(
                array(
                    'id' => new external_value(PARAM_INT, 'User ID'),
                    'fullname' => new external_value(PARAM_NOTAGS, 'User full name'),
                    'profileimageurl' => new external_value(PARAM_URL, 'User picture URL', VALUE_OPTIONAL),
                    'profileimageurlsmall' => new external_value(PARAM_URL, 'Small user picture URL', VALUE_OPTIONAL)
                )
            ),
            'List of contacts'
        );
    }