protected function getErrorMessage($retval, $file)
    {
        switch ($retval) {
            case ZipArchive::ER_EXISTS:
                return sprintf("File '%s' already exists.", $file);
            case ZipArchive::ER_INCONS:
                return sprintf("Zip archive '%s' is inconsistent.", $file);
            case ZipArchive::ER_INVAL:
                return sprintf("Invalid argument (%s)", $file);
            case ZipArchive::ER_MEMORY:
                return sprintf("Malloc failure (%s)", $file);
            case ZipArchive::ER_NOENT:
                return sprintf("No such zip file: '%s'", $file);
            case ZipArchive::ER_NOZIP:
                return sprintf("'%s' is not a zip archive.", $file);
            case ZipArchive::ER_OPEN:
                return sprintf("Can't open zip file: %s", $file);
            case ZipArchive::ER_READ:
                return sprintf("Zip read error (%s)", $file);
            case ZipArchive::ER_SEEK:
                return sprintf("Zip seek error (%s)", $file);
            default:
                return sprintf("'%s' is not a valid zip archive, got error code: %s", $file, $retval);
        }
    }