file_type (MIME::ContentTypes)

    # File lib/mime/content_types.rb, line 87
        def file_type file
          filename = file.respond_to?(:path) ? file.path : file
          extension = File.extname(filename)[1..-1] # array index removes period
          typ_exts = CONTENT_TYPES.find {|type, extentions| extentions.include? extension}
          typ_exts ? typ_exts.first : typ_exts      # returns +type+ from above or nil
        end