php - 这个下载错误的强制下载代码有什么问题？

Question

thisforce 下载代码出现错误下载有什么问题？

<?php

if (ini_get('zlib.output_compression'))
    ini_set('zlib.output_compression', 'Off');

$file_extension = strtolower(substr(strrchr($filename,"."),1));

$filename = $_GET['file'];

switch( $file_extension )
{     
    case "gif": $ctype="image/gif"; break;
    case "png": $ctype="image/png"; break;
    case "jpeg": $ctype="image/jpeg";
    case "jpg": $ctype="image/jpg"; break;
    case "mp3": $ctype="audio/mpeg3"; break;     
    case "mp3": $ctype="audio/x-mpeg-3"; break;
    case "mp3": $ctype="video/mpeg"; break;
    case "mp3": $ctype="video/x-mpeg"; break;
    case "mpa": $ctype="audio/mpeg"; break;
    case "mpa": $ctype="video/mpeg"; break;
    default: $ctype="application/force-download";
}

header("Pragma: public"); 
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");

header("Content-Type: $ctype"); 
header("Content-Disposition: attachment;filename=\"".basename($filename)."\";" );  

header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($filename));
readfile("$filename");
exit();

?>

Answer 1

我自己找到的，标头 Content-Type 必须是：

 header("Content-Type: ".$filename->mediaType);