PHP readfile下载文件

PHP下载文件，经测试Android、IOS均可用

// 文件路径
function download($file){
  if (file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="'.basename($file).'"');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    readfile($file);
    exit;
  }else{
    exit($file."文件不存在");
  }
}