protected function getPartBodyFromFile(&$part)
    {
        $start = $part['starting-pos-body'];
        $end = $part['ending-pos-body'];
        $body = '';
        if ($end - $start > 0) {
            fseek($this->stream, $start, SEEK_SET);
            $body = fread($this->stream, $end - $start);
        }

        return $body;
    }