hints: change the handling of repeated hints (again)

In reverse (PTR) records, now the last definition wins,
and non-canonical names don't get (shadowed) records.

lib/generic/pack.h

@@ -23,6 +23,8 @@
  * backed by an array.
  *
  * @note Maximum object size is 2^16 bytes, see  ::pack_objlen_t
+ * @TODO If some mistake happens somewhere, the access may end up in an infinite loop.
+ *       (equality comparison on pointers)
  *
  * # Example usage:
  *
@@ -113,6 +115,23 @@ static inline uint8_t *pack_obj_next(uint8_t *it)
 	return pack_obj_val(it) + pack_obj_len(it);
 }
 
+/** Return pointer to the last packed object. */
+static inline uint8_t *pack_last(pack_t pack)
+{
+	if (pack.len == 0) {
+		return NULL;
+	}
+	uint8_t *it = pack_head(pack);
+	uint8_t *tail = pack_tail(pack);
+	while (true) {
+		uint8_t *next = pack_obj_next(it);
+		if (next == tail) {
+			return it;
+		}
+		it = next;
+	}
+}
+
 /** Push object to the end of the pack
   * @return 0 on success, negative number on failure
   */

modules/hints/hints.c

@@ -83,7 +83,7 @@ static int satisfy_reverse(struct kr_zonecut *hints, knot_pkt_t *pkt, struct kr_
 	knot_rrset_init(&rr, qname, KNOT_RRTYPE_PTR, KNOT_CLASS_IN);
 
 	/* Append address records from hints */
-	uint8_t *addr = pack_head(*addr_set);
+	uint8_t *addr = pack_last(*addr_set);
 	if (addr != NULL) {
 		size_t len = pack_obj_len(addr);
 		void *addr_val = pack_obj_val(addr);
@@ -334,8 +334,12 @@ static int load_map(struct hints_data *data, FILE *fp)
 			continue;
 		}
 		char *name_tok = strtok_r(NULL, " \t\n", &saveptr);
+		bool canonical_name = true;
 		while (name_tok != NULL) {
-			add_reverse_pair(&data->reverse_hints, name_tok, tok);
+			if (canonical_name) {
+				add_reverse_pair(&data->reverse_hints, name_tok, tok);
+				canonical_name = false;
+			}
 			if (add_pair(&data->hints, name_tok, tok) == 0) {
 				count += 1;
 			}