php保存远程文件到本地的方法

用到了ob_start();
<?php
header("Content-type:text/html  charset=utf-8");
if(!empty($_POST['post'])){
       $url=$_POST['url'];
       $fileName=$_POST['fileName'];
       $fileName=grabImage($url,$fileName);
       echo "<img src=\"$fileName\" width='300px' height='300px'/>";
}

function  grabImage($url,$fileName){
        if($url=="") return false;
        $p=strrpos($url,".");
        $exp=substr($url,$p+1);
        if($fileName=="") $fileName=mt_rand(100000,999999).".".$ext;
        if($exp=="gif" || $exp=="jepg" || $exp=="png" || $exp=="jpg"){

                ob_start();
                readfile($url);
                $content=ob_get_contents();
                ob_end_clean();
                $f=fopen($fileName,"w");
                fwrite($f,$content);
                fclose($f);
        }else{
                return  false;
        }
        return $fileName;
}

?>

<form  action="" method="post">
图片地址：<input type="text" name="url" /><br/>
保存地址：<input type="text" name="fileName"/><br/>
<input type="submit" name="post" value="下载"/>
</form>