expires_in (ActionController::Base)

    # File lib/action_controller/base.rb, line 1216
          def expires_in(seconds, options = {}) #:doc:
            cache_control = response.headers["Cache-Control"].split(",").map {|k| k.strip }

            cache_control << "max-age=#{seconds}"
            cache_control.delete("no-cache")
            if options[:public]
              cache_control.delete("private")
              cache_control << "public"
            else
              cache_control << "private"
            end

            # This allows for additional headers to be passed through like 'max-stale' => 5.hours
            cache_control += options.symbolize_keys.reject{|k,v| k == :public || k == :private }.map{ |k,v| v == true ? k.to_s : "#{k.to_s}=#{v.to_s}"}

            response.headers["Cache-Control"] = cache_control.join(', ')
          end