How to limit download speed in php

/**
 desc: limit download speed
 link: bbs.it-home.org
 date: 2013/2/25
*/
// local file that should be send to the client
$local_file = 'test-file.zip';
// filename that the user gets as default
$download_file = 'your-download-name.zip';
// set the download rate limit (=> 20,5 kb/s)
$download_rate = 20.5;
if(file_exists($local_file) && is_file($local_file)) {
 // send headers
 header('Cache-control: private');
 header('Content-Type: application/octet-stream');
 header('Content-Length: '.filesize($local_file));
 header('Content-Disposition: filename='.$download_file);
 // flush content
 flush();
 // open file stream
 $file = fopen($local_file, "r");
 while (!feof($file)) {
 // send the current file part to the browser
 print fread($file, round($download_rate * 1024));
 // flush the content to the browser
 flush();
 // sleep one second
 sleep(1);
 }
 // close file stream
 fclose($file);
}
else {
 die('Error: The file '.$local_file.' does not exist!');
}
?>

附：修改Discuz论坛实现对附件下载的限速

研究了一下Discuz的代码，实现了一个可行的方案。 很简单，找到attachment.pnp，找到最下面，有个： function getlocalfile($filename, $readmod = 1, $range = 0)

修改为：

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();
}
?>

经过测试，发现效果还是很明显的。