通过php程序进行文件下载

<?php
    
    $file_name = $_GET['file'] . ".apk";
    
    $file_dir = $_SERVER['DOCUMENT_ROOT'] . "\\";
    
    if(!file_exists($file_dir . $file_name)) {
        
        echo "file is not exists";
        
    } else {
        
        $file = fopen($file_dir . $file_name, "r");
        
        header("Content-type: application/vnd.android.package-archive");
        
        header("Accept-Ranges: bytes");
        
        header("Accept-Length: ".filesize($file_dir . $file_name));
        
        header("Content-Disposition: attachment; filename=" . $file_name); 
    
        echo fread($file,filesize($file_dir . $file_name)); 
        
        fclose($file);

        exit;
    }
?>