let same_service_opt sp s sopt =
let same_url url = make_uri ~absolute_path:true ~sp ~service:s () = url in
match sopt with
| None -> (* MAYBE : use this or get_original_full_path_string *)
same_url ("/" ^ Eliom_sessions.get_current_full_path_string sp)
| Some s' -> same_url (make_uri ~absolute_path:true ~service:s' ~sp ())