php强制下载文件函数

public function down()

{
  $id = $this->_get('id');
  $m = m("downloads");
  $data=$m->where("id=$id and status=1")->find();
  !$data && exit;
  $filename = iconv('utf-8','gbk',$data['filename']);
  $savename = $data['savename']; 
  $myfile = $data[url] ? $data[url] : 'uploads/file/'.$savename;
  if(file_exists($myfile)){
  　　$m->where("id=$id")->setinc('downloads');
  　　$file = @ fopen($myfile, "r");
  　　header("content-type: application/octet-stream");
  　　header("content-disposition: attachment; filename=" .$filename );
  　　while (!feof($file)) {
    echo fread($file, 50000);
  　　}
  　　fclose($file);
  　　exit;
  }else{
  　　echo '文件不存在！';

  }
}