Fix bug in loop-detection: the new TTL-updating was confusing the set

proxy.rkt

@@ -190,10 +190,11 @@
 	       (transition w (send-message (answered-question q #f)))]
 	      [(network-reply (== referral-id) ans)
 	       (define-values (new-zone ignored-timers) (incorporate-complete-answer ans zone))
+	       (define nameserver-names (for/set ([rr nameserver-rrs]) (rr-rdata rr)))
 	       (extend-transition
 		   (retry-question (struct-copy question-state w
 						[nameservers-tried (set-union nameservers-tried
-									      nameserver-rrs)]
+									      nameserver-names)]
 						[zone new-zone]
 						[retry-count (+ old-retry-count 1)]))
 		 (unsubscribe referral-id))])))]

resolver.rkt

@@ -100,7 +100,7 @@
 (define (closest-untried-nameservers q zone nameservers-tried)
   (define name (question-name q))
   (define ns-rrset (closest-nameservers name zone))
-  (set-subtract ns-rrset nameservers-tried))
+  (for/set ([rr ns-rrset] #:when (not (set-member? nameservers-tried (rr-rdata rr)))) rr))
 
 (define (empty-answer q zone start-of-authority)
   (if (and start-of-authority ;; we are authoritative for something