文件在php中下载

Question

function download($data = false){
            $file_name = '2013-07-01-093847test';   
    $extension = 'txt'; 
    $filename = $file_name.".".$extension;
    $upload_folder='path\to\folder\';
    $uploadDir = WWW_ROOT.$upload_folder;
    $file=$uploadDir.'\\'.$file_name;
    $new_file=$uploadDir.'\\'.$filename;
    copy($file, $new_file); 
    $ext = end(explode('.',$new_file));
    if($ext && array_key_exists($ext,$file_types)){
          if(file_exists($new_file)) {
             header('Content-Description: File Transfer');
             header('Content-Type: application/stream');
             header('Content-Disposition: attachment; filename='.basename($new_file));
             header('Content-Transfer-Encoding: binary');
             header('Expires: 78000');
             header('Cache-Control: private');
             header('Pragma: public');
             header('Content-Length: ' . filesize($new_file));
             #readfile($new_file);
             unlink($new_file);
             exit;
          }
    }
    else {
        die('The provided file path is not valid.');
    }
}

当我尝试使用extjs界面中的上述代码下载文件时，文件内容会显示在firebug控制台部分而不会下载到客户端计算机上？