public function putFileContents($filePath, $string)
    {
        if ($this->fileIsReadable($filePath) === true) {
            // Existing file. Most likely a html log file.
            file_put_contents($filePath, $string, FILE_APPEND);
            return;
        }

        // New file. We tell the caching, that we have read access here.
        file_put_contents($filePath, $string, FILE_APPEND);
        static::$isReadableCache[$filePath] = true;
    }