class GdsApi::JsonClient

def response_cache_time(response)

or nil if no cache information is provided
Return either a Time object representing the expiry time of the response 
def response_cache_time(response)
  if response.headers[:cache_control]
    cache_control = Rack::Cache::CacheControl.new(response.headers[:cache_control])
    if cache_control.private? || cache_control.no_cache? || cache_control.no_store?
      Time.now.utc
    elsif cache_control.max_age
      Time.now.utc + cache_control.max_age
    end
  elsif response.headers[:expires]
    Time.httpdate response.headers[:expires]
  end
end