I would not trust file extensions; File::MMagic seems to me a better solution; here is an untested snippet:

use File::MMagic;
$mm = new File::MMagic; # use internal magic file
# disable checks made against file extension
$mm->removeFileExts;
$type = $mm->checktype_filename("/somewhere/unknown/file");
...
[download]

$type will contain a MIME mediatype string.

HTH, Valerio