Detect MIME type of uploaded file in Ruby

Question

Is there a bullet proof way to detect MIME type of uploaded file in Ruby or Ruby on Rails? I'm uploading JPEGs and PNGs using SWFupload and content_type is always "application/octet-stream"

Answer 1

The ruby-filemagic gem will do it:

require 'filemagic'

puts FileMagic.new(FileMagic::MAGIC_MIME).file(__FILE__)
# => text/x-ruby; charset=us-ascii

This gem does not look at the file extension at all. It reads a bit of the file contents and uses that to guess the file's type.