resolved: add dns_answer_contains() helper

src/resolve/resolved-dns-answer.c

@@ -284,6 +284,16 @@ int dns_answer_contains_zone_nsec3(DnsAnswer *answer, const char *zone) {
         return false;
 }
 
+int dns_answer_contains(DnsAnswer *answer, DnsResourceRecord *rr) {
+        DnsResourceRecord *i;
+
+        DNS_ANSWER_FOREACH(i, answer)
+                if (dns_resource_record_equal(i, rr))
+                        return true;
+
+        return false;
+}
+
 int dns_answer_find_soa(DnsAnswer *a, const DnsResourceKey *key, DnsResourceRecord **ret, DnsAnswerFlags *flags) {
         DnsResourceRecord *rr, *soa = NULL;
         DnsAnswerFlags rr_flags, soa_flags = 0;

src/resolve/resolved-dns-answer.h

@@ -47,6 +47,7 @@ int dns_answer_add_soa(DnsAnswer *a, const char *name, uint32_t ttl, int ifindex
 int dns_answer_match_key(DnsAnswer *a, const DnsResourceKey *key, DnsAnswerFlags *combined_flags);
 int dns_answer_contains_nsec_or_nsec3(DnsAnswer *a);
 int dns_answer_contains_zone_nsec3(DnsAnswer *answer, const char *zone);
+int dns_answer_contains(DnsAnswer *answer, DnsResourceRecord *rr);
 
 int dns_answer_find_soa(DnsAnswer *a, const DnsResourceKey *key, DnsResourceRecord **ret, DnsAnswerFlags *flags);
 int dns_answer_find_cname_or_dname(DnsAnswer *a, const DnsResourceKey *key, DnsResourceRecord **ret, DnsAnswerFlags *flags);