don't bother caching invalid or very short lived responses

diff --git a/usr.sbin/rebound/rebound.c b/usr.sbin/rebound/rebound.c
index 3b6d514..03c9333 100644 (file)
--- a/usr.sbin/rebound/rebound.c
+++ b/usr.sbin/rebound/rebound.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: rebound.c,v 1.85 2017/07/03 09:39:48 tedu Exp $ */
+/* $OpenBSD: rebound.c,v 1.86 2017/07/03 16:36:48 tedu Exp $ */
 /*
  * Copyright (c) 2015 Ted Unangst <tedu@openbsd.org>
  *
@@ -72,7 +72,7 @@ struct dnspacket {
 /*
  * requests will point to cache entries until a response is received.
  * until then, the request owns the entry and must free it.
- * after it's on the list, the request must not free it.
+ * after the response is set, the request must not free it.
  */
 struct dnscache {
        TAILQ_ENTRY(dnscache) fifo;
@@ -433,16 +433,17 @@ sendreply(struct request *req)
        }
        sendto(req->client, buf, r, 0, &req->from.a, req->fromlen);
        if ((ent = req->cacheent)) {
+               /* check that the response is worth caching */
+               ttl = minttl(resp, r);
+               if (ttl == -1 || ttl == 0)
+                       return;
                /*
-                * we do this first, because there's a potential race against
+                * we do this next, because there's a potential race against
                 * other requests made at the same time. if we lose, abort.
                 * if anything else goes wrong, though, we need to reverse.
                 */
                if (RB_INSERT(cachetree, &cachetree, ent))
                        return;
-               ttl = minttl(resp, r);
-               if (ttl == -1)
-                       ttl = 0;
                ent->ts = now;
                ent->ts.tv_sec += MINIMUM(ttl, 300);
                ent->resp = malloc(r);