强制下载PHP - 不下载整个文件

我在强制下载某些mp3/zip文件时遇到问题。

问题是一些用户体验到整个文件没有下载，我不知道为什么。

if(is_file($file_name))
{
    /*
        Do any processing you'd like here:
        1.  Increment a counter
        2.  Do something with the DB
        3.  Check user permissions
        4.  Anything you want!
    */
    // required for IE
    if(ini_get('zlib.output_compression')) { ini_set('zlib.output_compression', 'Off'); }
    // get the file mime type using the file extension
    switch(strtolower(substr(strrchr($file_name,'.'),1)))
    {
        case 'mp3': $mime = 'audio/mpeg'; break;
        case 'zip': $mime = 'application/zip'; break;
        default: $mime = 'application/force-download';
    }
    header('Pragma: public');   // required
    header('Expires: 0');       // no cache
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Last-Modified: '.gmdate ('D, d M Y H:i:s', filemtime ($file_name)).' GMT');
    header('Cache-Control: private',false);
    header('Content-Type: '.$mime);
    header('Content-Disposition: attachment; filename="'.basename($file_name).'"');
    header('Content-Transfer-Encoding: binary');
    header('Content-Length: '.filesize($file_name));    // provide file size
    header('Connection: close');
    readfile($file_name);       // push it out
    exit();
}

这是我的代码..

有什么想法吗？