Download a file from web Server - php

Question

I have a web running on a server and I manage several files. I want users can download a certain files generated but I can't force to download this files, and I tried several ways to do it. Mails with files attached (3 different ways) or by forcing the file download through the web browser... Nothing happens.
I have this configuration in JS (jQuery) to PHP script:
$.ajax({
type: "POST",
url: "./download_file.php",
data: {download_file: jsonFilename},
cache: false,
success: function(data){
alert(data);
}
});
In PHP force download:
$file = json_decode($_POST['download_file']);
header("Content-type: application/octet-stream");
header("Content-disposition: attachment; filename=" . $file);
readfile("./uploads/subtitles/" . $file);
In PHP PHPMailer:
require_once('./PHPMailer-master/class.phpmailer.php');
$file = json_decode($_POST['download_file']);
$bodytext = 'Here is your file!';
$email = new PHPMailer();
$email->From = 'admin#mail.com';
$email->FromName = 'Web Administrator';
$email->Subject = 'Download';
$email->Body = $bodytext;
$email->AddAddress( 'user#mail.co' );
$file_to_attach = './path/' . $file;
$email->AddAttachment( $file_to_attach , $file );
return $email->Send();
Also I tried this other way in PHP:
function mail_attachment($filename, $path, $mailto,$from_mail, $from_name, $replyto, $subject, $message) {
$file = $path.$filename;
$file_size = filesize($file);
$handle = fopen($file, "r");
$content = fread($handle, $file_size);
fclose($handle);
$content = chunk_split(base64_encode($content));
$uid = md5(uniqid(time()));
$header = "From: ".$from_name." <".$from_mail.">\r\n";
$header .= "Reply-To: ".$replyto."\r\n";
$header .= "MIME-Version: 1.0\r\n";
$header .= "Content-Type: multipart/mixed; boundary=\"".$uid."\"\r\n\r\n";
$header .= "This is a multi-part message in MIME format.\r\n";
$header .= "--".$uid."\r\n";
$header .= "Content-type:text/plain; charset=iso-8859-1\r\n";
$header .= "Content-Transfer-Encoding: 7bit\r\n\r\n";
$header .= $message."\r\n\r\n";
$header .= "--".$uid."\r\n";
$header .= "Content-Type: application/octet-stream; name=\"".$filename."\"\r\n"; // use different content types here
$header .= "Content-Transfer-Encoding: base64\r\n";
$header .= "Content-Disposition: attachment; filename=\"".$filename."\"\r\n\r\n";
$header .= $content."\r\n\r\n";
$header .= "--".$uid."--";
if (mail($mailto, $subject, "", $header)) {
echo "mail send ... OK"; // or use booleans here
} else {
echo "mail send ... ERROR!";
}
}
$file = json_decode($_POST['download_file']);
$bodytext = 'Here is your file';
//start editing and inputting attachment details here
$my_file = $file;
$my_path = "./path/";
$my_name = "Web Administrator";
$my_mail = "admin#mail.com";
$my_replyto = "admin#mail.com";
$my_subject = "whatever";
$my_message = $bodytext;
mail_attachment($my_file, $my_path, "user#mail.co", $my_mail, $my_name, $my_replyto, $my_subject, $my_message);
I only want user gets his file, but nothing seems to work by the moment.
My web is running on a CentOS server and web-server lighthttpd.
Thank you