merge_and_normalize_cache_control!

# File actionpack/lib/action_dispatch/http/cache.rb, line 183
        def merge_and_normalize_cache_control!(cache_control)
          control = cache_control_headers

          return if control.empty? && cache_control.empty?  # Let middleware handle default behavior

          if cache_control.any?
            # Any caching directive coming from a controller overrides
            # no-cache/no-store in the default Cache-Control header.
            control.delete(:no_cache)
            control.delete(:no_store)

            if extras = control.delete(:extras)
              cache_control[:extras] ||= []
              cache_control[:extras] += extras
              cache_control[:extras].uniq!
            end

            control.merge! cache_control
          end

          options = []

          if control[:no_store]
            options << PRIVATE if control[:private]
            options << NO_STORE
          elsif control[:no_cache]
            options << PUBLIC if control[:public]
            options << NO_CACHE
            options.concat(control[:extras]) if control[:extras]
          else
            extras = control[:extras]
            max_age = control[:max_age]
            stale_while_revalidate = control[:stale_while_revalidate]
            stale_if_error = control[:stale_if_error]

            options << "max-age=#{max_age.to_i}" if max_age
            options << (control[:public] ? PUBLIC : PRIVATE)
            options << MUST_REVALIDATE if control[:must_revalidate]
            options << "stale-while-revalidate=#{stale_while_revalidate.to_i}" if stale_while_revalidate
            options << "stale-if-error=#{stale_if_error.to_i}" if stale_if_error
            options.concat(extras) if extras
          end

          self._cache_control = options.join(", ")
        end