protected function _writeBackDataOut($out, $data)
    {
        $buck = stream_bucket_new($this->bufferHandle, '');
        if (false === $buck)
            // trigger filter error
            return PSFS_ERR_FATAL;

        $buck->data = $data;
        stream_bucket_append($out, $buck);

        // data was processed successfully
        return PSFS_PASS_ON;
    }