resolved: add authority section to mDNS probing queries

According to RFC 6762 Section 8.2 "Simultaneous Probe Tiebreaking"
probing queries' Authority Section is populated with proposed
resource records in order to resolve possible race conditions.

diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index a66d60540534de98933f8a10761b2cb5529f2de0..ea81056119b842c54067aacdd92b069cee0a3266 100644 (file)
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -1377,7 +1377,11 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
         bool add_known_answers = false;
         DnsTransaction *other;
+        Iterator i;
+        DnsResourceKey *tkey;
+        _cleanup_set_free_ Set *keys = NULL;
         unsigned qdcount;
+        unsigned nscount = 0;
         usec_t ts;
         int r;
 
@@ -1400,6 +1404,16 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
         if (dns_key_is_shared(t->key))
                 add_known_answers = true;
 
+        if (t->key->type == DNS_TYPE_ANY) {
+                r = set_ensure_allocated(&keys, &dns_resource_key_hash_ops);
+                if (r < 0)
+                        return r;
+
+                r = set_put(keys, t->key);
+                if (r < 0)
+                        return r;
+        }
+
         /*
          * For mDNS, we want to coalesce as many open queries in pending transactions into one single
          * query packet on the wire as possible. To achieve that, we iterate through all pending transactions
@@ -1459,6 +1473,16 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
 
                 if (dns_key_is_shared(other->key))
                         add_known_answers = true;
+
+                if (other->key->type == DNS_TYPE_ANY) {
+                        r = set_ensure_allocated(&keys, &dns_resource_key_hash_ops);
+                        if (r < 0)
+                                return r;
+
+                        r = set_put(keys, other->key);
+                        if (r < 0)
+                                return r;
+                }
         }
 
         DNS_PACKET_HEADER(p)->qdcount = htobe16(qdcount);
@@ -1470,6 +1494,22 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
                         return r;
         }
 
+        SET_FOREACH(tkey, keys, i) {
+                _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+                bool tentative;
+
+                r = dns_zone_lookup(&t->scope->zone, tkey, t->scope->link->ifindex, &answer, NULL, &tentative);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_append_answer(p, answer);
+                if (r < 0)
+                        return r;
+
+                nscount += dns_answer_size(answer);
+        }
+        DNS_PACKET_HEADER(p)->nscount = htobe16(nscount);
+
         t->sent = p;
         p = NULL;