Cache\Adapter\Filesystem\FilesystemCachePool::getFilePath PHP Method

    private function getFilePath($key)
    {
        if (!preg_match('|^[a-zA-Z0-9_\\.! ]+$|', $key)) {
            throw new InvalidArgumentException(sprintf('Invalid key "%s". Valid keys must match [a-zA-Z0-9_\\.! ].', $key));
        }
        return sprintf('%s/%s', $this->folder, $key);
    }