module Sinatra::Helpers

=> Expires: Mon, 08 Jun 2009 08:50:17 GMT
=> Cache-Control: public, must-revalidate, max-age=500
expires 500, :public, :must_revalidate

"values" arguments are passed to the #cache_control helper:
indicating when the response should be considered "stale". The remaining
can be an integer number of seconds in the future or a Time object
Set the Expires header and Cache-Control/max-age directive. Amount

def expires(amount, *values)
  values << {} unless values.last.is_a?(Hash)
  if amount.is_a? Integer
    time    = Time.now + amount.to_i
    max_age = amount
  else
    time    = time_for amount
    max_age = time - Time.now
  end
  values.last.merge!(max_age: max_age) { |_key, v1, v2| v1 || v2 }
  cache_control(*values)
  response['Expires'] = time.httpdate
end