php 下載限速

function getlocalfile($filename, $readmod = 1, $range = 0)
{
    if ($fp = @fopen($filename, 'rb')) {
        @fseek($fp, $range);
        $download_rate = 10;//限制网速10kb/s
        while (! feof($fp)) {
            print fread($fp, round($download_rate * 1024));
            flush();
            ob_flush();
            sleep(1);
        }
    }
    @fclose($fp);
    @flush();
    @ob_flush();
}