php - Utility of HTTP header "Content-Type: application/force-download" for mobile?

Question

I am currently working on a PHP script that allows you to download media contents (video, audio, pictures...) from your mobile device by accessing a link. (i.e. http://www.my-web-site.com/download.php?id=7ejs8ap) My script worked very vell when I was testing it with recent mobile (Samsung Galaxy S, iPhone 4S, some others...) but an error occured on my old mobile Samsung C3050. The media I wanted to download was just an audio mp3 file that I usually download easily.

The error appears to be "Unknown content type." So, as my only HTTP header Content-Type was "application/force-download", I try to comment this and try again. Then, it works. But now, I am currently asking what this Content-Type means and if it can be mandatory for others mobile. I tested without the Content-Type on the iPhone 4 and it works, but I'm not sure of this compatibility for all mobile.

Can someone explain me how that Content-Type works, why this isn't a standard MIME or everything else that can help me to be sure this is an optionnal Content-Type for every download, whatever the file, the browser or the device I am downloading on?

Thanks everyone.

Here is my PHP headers sent:

<?php
//Assume that $filename and $filePath are correclty set.
header('Content-Description: File Transfer');
header('Content-Disposition: attachment; filename="'.$filename.'"');
// header('Content-Type: application/force-download'); Non-standard MIME-Type, incompatible with Samsung C3050 for example. Let it commented
readfile($filePath);
?>

EDIT : I just tried with a Sony Xperia, and the download wasn't successful: I only see the "html-encoded" bytes of my file I want to download. How can I know what content-type I have to use if application/octet-stream or application/force-download doesn't work?

Answer 1

Content-Type: application/force-download means "I, the web server, am going to lie to you (the browser) about what this file is so that you will not treat it as a PDF/Word Document/MP3/whatever and prompt the user to save the mysterious file to disk instead". It is a dirty hack that breaks horribly when the client doesn't do "save to disk".

Use the correct mime type for whatever media you are using (e.g. audio/mpeg for mp3).

Use the Content-Disposition: attachment; etc etc header if you want to encourage the client to download it instead of following the default behaviour.