@chaizhenhua  "why not use copy_response_headers_from_ngx? they share some same code."
Because we may end up adding a Date header - we would need to call `ComputeCaching()` twice. 
Also note the comment `We need to investigate why we don't receive it.`: this date handling might not be the proper solution. If it is though, we should probably refactor it to use `copy_response_headers_from_ngx()` like you mention