# File lib/paperclip/interpolations.rb, line 104
    def content_type_extension attachment, style_name
      mime_type = MIME::Types[attachment.content_type]
      extensions_for_mime_type = unless mime_type.empty?
        mime_type.first.extensions
      else
        []
      end

      original_extension = extension(attachment, style_name)
      if extensions_for_mime_type.include? original_extension
        original_extension
      elsif !extensions_for_mime_type.empty?
        extensions_for_mime_type.first
      else
        # It's possible, though unlikely, that the mime type is not in the
        # database, so just use the part after the '/' in the mime type as the
        # extension.
        %r{/([^/]*)$}.match(attachment.content_type)[1]
      end
    end