PHP readfile return data - php

Question

(my first question on stack, so sorry for errors and/or inaccuracies...)
So : I've developed a Wordpress Theme and I'd like my users to download the attachments of a post. So I created a Zip Archive and use a readfile(). The function is called by link and using a $_GET['zip'] test.
The Problem : readfile() returns (i mean display) binary characters like this (here I tried to download a test .png file) : �PNG IHDRp�r�*� pHYs�� OiCCPPhotoshop ICC profilexڝSgTS�=���BK���KoR
And nothing is downloaded.
Here my code (the readfile part) :
$zip = new ZipArchive();
if ($zip->open($file_path.$archive_file_name, ZIPARCHIVE::CREATE)!==TRUE) {
exit("cannot open <$archive_file_name>\n");
}
foreach($file_names as $file){
$zip->addFile($file,$file);
}
$zip->close();
header('Content-Description: File Transfer');
header('Content-Type: application/zip');
header('Content-Disposition: attachment; filename="'.basename($file_path.$file).'"');
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($file_path.$file));
ob_clean();
flush();
readfile($file_path.'screenshot.png');
I don't know where to search, and it's my first time with zip archive AND readfile()...
Thanks for the tracks (? do we say that? ) !

Answer 1

I don't know how exactly but it works now. I added an ob_start() just at the beginning of the function. Thanks for support !
The entire function :
if (!function_exists('zipThoseFiles')) {
ob_start();
function zipThoseFiles($id){
if (!function_exists('zipFilesDownload')) {
function zipFilesDownload($file_names,$archive_file_name,$file_path){
$zip = new ZipArchive();
if ($zip->open($file_path.$archive_file_name, ZIPARCHIVE::CREATE )!==TRUE) {
exit("cannot open <$archive_file_name>\n");
}
foreach($file_names as $file){
$zip->addFile($file,$file);
}
$zip->close();
header('Content-Description: File Transfer');
header('Content-Type: application/zip');
header('Content-Disposition: attachment; filename="'.basename($file_path.$archive_file_name).'"');
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($file_path.$archive_file_name));
ob_end_clean();
flush();
readfile($file_path.$archive_file_name);
unlink($file_path.$archive_file_name);
exit;
}
}
$fileNames = array();
$args = array(
'post_type' => 'attachment',
'numberposts' => null,
'post_status' => null,
'post_parent' => $id
);
$attachments = get_posts($args);
if ($attachments) {
foreach ($attachments as $attachment) {
$fileNames[] = get_attached_file( $attachment->ID );
}
}
$zip_file_name = 'mediasArchive.zip';
$file_path = dirname(__FILE__).'/';
zipFilesDownload($fileNames,$zip_file_name,$file_path);
}
}