Rack Middleware or after filter

Hi All
           I need an solution that i should catch response and based
on some conditions i have to modify response body and send back to
client.

      I have tried with a Middleware and got a solution.Can i use a
Middleware or simply one after_filter.
On performance wise which is best.Or is there any other ways to do it.

                           thanks in advance.

If you are letting the request go through the Rails stack already I
don't see how you can make the response go any faster either way. If
you were catching the request in the middleware on its way to the
Rails stack and returned right away without going through Rails then
it would be a different story and the response would be faster.