module ActionDispatch::Http::Cache::Response

def set_conditional_cache_control!
  control = {}
  cc_headers = cache_control_headers
  if extras = cc_headers.delete(:extras)
    @cache_control[:extras] ||= []
    @cache_control[:extras] += extras
    @cache_control[:extras].uniq!
  end
  control.merge! cc_headers
  control.merge! @cache_control
  if control.empty?
    headers[CACHE_CONTROL] = DEFAULT_CACHE_CONTROL
  elsif control[:no_cache]
    headers[CACHE_CONTROL] = NO_CACHE
    if control[:extras]
      headers[CACHE_CONTROL] += ", #{control[:extras].join(', ')}"
    end
  else
    extras  = control[:extras]
    max_age = control[:max_age]
    options = []
    options << "max-age=#{max_age.to_i}" if max_age
    options << (control[:public] ? PUBLIC : PRIVATE)
    options << MUST_REVALIDATE if control[:must_revalidate]
    options.concat(extras) if extras
    headers[CACHE_CONTROL] = options.join(", ")
  end
end