这么为什么不能实现文件下载

<?php<br />$root="D:/ghost/";<br />if(is_dir($root)){<br />   $openHandle=opendir($root);<br />   while(false!==($file=readdir($openHandle))){<br />	   if(!is_dir($root.$file)){<br />		 echo "<a href='?do=down&file=".$file."&path=".urlencode($root)."'>".$root.$file."</a><br/>";<br />	   }<br />   }<br />   closedir($openHandle);<br />}else{<br />echo "文件夹不存在";<br />}<br /><br />$do=(isset($_REQUEST['do'])) ? addslashes($_REQUEST['do']) : '';<br />if($do=='down') {<br />	$file=(isset($_REQUEST['file'])) ? addslashes($_REQUEST['file']) : '';<br />	$path=(isset($_REQUEST['path'])) ? addslashes($_REQUEST['path']) : '';<br /><br />	OB_start();<br />	function DownLoad($info,$file) {<br />		OB_Clean();<br />		if(!file_exists($info)) {<br />			exit('Error:'.__LINE__.','.basename(__FILE__).'!');<br />		}<br />		$info=file_get_contents($info);<br /><br />		header('Content-Transfer-Encoding: binary');<br />		header('Content-Type: application/force-download; name="'.$file.'"');<br />		header('Content-Disposition: attachment; filename='.$file.'');<br />		header('Cache-control: private');<br />		header('Pragma: no-cache');<br />		header('Expires: 0');<br />		echo $info;<br />		die();<br />	}<br />	DownLoad($path.$file,$file);<br />}