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.

Answer 2

In Ruby on Rails you can do:

MIME::Types.type_for("filename.gif").first.content_type # => "image/gif"