# File lib-plugins/yapra/plugin/publish/file_download.rb, line 32
    def discover_extensions page
      require 'mime/types'
      types = MIME::Types[page.content_type]
      if types.size > 0 && types[0].extensions.size > 0
        return type[0].extensions[0]
      else
        logger.info 'suitable extention is not found.'
        return nil
      end
    rescue LoadError => ex
      logger.warn 'require mime-types is failed.'
    end