resolved: store just the DnsAnswer instead of a DnsPacket as answer in DnsTransaction objects

Previously we'd only store the DnsPacket in the DnsTransaction, and the
DnsQuery would then take the DnsPacket's DnsAnswer and return it. With
this change we already pull the DnsAnswer out inside the transaction.

We still store the DnsPacket in the transaction, if we have it, since we
still need to determine from which peer a response originates, to
implement caching properly. However, the DnsQuery logic doesn't care
anymore for the packet, it now only looks at answers and rcodes from the
successfuly candidate.

This also has the benefit of unifying how we propagate incoming packets,
data from the local zone or the local cache.

1 files changed, 18 insertions, 7 deletions

diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index 2fc84aec6f..ef5097db39 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -39,7 +39,8 @@ DnsTransaction* dns_transaction_free(DnsTransaction *t) {
 
         dns_packet_unref(t->sent);
         dns_packet_unref(t->received);
-        dns_answer_unref(t->cached);
+
+        dns_answer_unref(t->answer);
 
         sd_event_source_unref(t->dns_udp_event_source);
         safe_close(t->dns_udp_fd);
@@ -137,6 +138,9 @@ static void dns_transaction_stop(DnsTransaction *t) {
 
         t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
         t->stream = dns_stream_free(t->stream);
+
+        /* Note that we do not drop the UDP socket here, as we want to
+         * reuse it to repeat the interaction. */
 }
 
 static void dns_transaction_tentative(DnsTransaction *t, DnsPacket *p) {
@@ -315,6 +319,8 @@ static int dns_transaction_open_tcp(DnsTransaction *t) {
         dns_server_unref(t->server);
         t->server = dns_server_ref(server);
         t->received = dns_packet_unref(t->received);
+        t->answer = dns_answer_unref(t->answer);
+        t->answer_rcode = 0;
         t->stream->complete = on_stream_complete;
         t->stream->transaction = t;
 
@@ -454,6 +460,11 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
                 return;
         }
 
+        /* Install the answer as answer to the transaction */
+        dns_answer_unref(t->answer);
+        t->answer = dns_answer_ref(p->answer);
+        t->answer_rcode = DNS_PACKET_RCODE(p);
+
         /* Only consider responses with equivalent query section to the request */
         if (p->question->n_keys != 1 || dns_resource_key_equal(p->question->keys[0], t->key) <= 0) {
                 dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
@@ -624,18 +635,18 @@ int dns_transaction_go(DnsTransaction *t) {
         t->n_attempts++;
         t->start_usec = ts;
         t->received = dns_packet_unref(t->received);
-        t->cached = dns_answer_unref(t->cached);
-        t->cached_rcode = 0;
+        t->answer = dns_answer_unref(t->answer);
+        t->answer_rcode = 0;
 
         /* Check the zone, but obly if this transaction is not used
          * for probing or verifying a zone item. */
         if (set_isempty(t->zone_items)) {
 
-                r = dns_zone_lookup(&t->scope->zone, t->key, &t->cached, NULL, NULL);
+                r = dns_zone_lookup(&t->scope->zone, t->key, &t->answer, NULL, NULL);
                 if (r < 0)
                         return r;
                 if (r > 0) {
-                        t->cached_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
                         dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                         return 0;
                 }
@@ -653,11 +664,11 @@ int dns_transaction_go(DnsTransaction *t) {
                 /* Let's then prune all outdated entries */
                 dns_cache_prune(&t->scope->cache);
 
-                r = dns_cache_lookup(&t->scope->cache, t->key, &t->cached_rcode, &t->cached);
+                r = dns_cache_lookup(&t->scope->cache, t->key, &t->answer_rcode, &t->answer);
                 if (r < 0)
                         return r;
                 if (r > 0) {
-                        if (t->cached_rcode == DNS_RCODE_SUCCESS)
+                        if (t->answer_rcode == DNS_RCODE_SUCCESS)
                                 dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                         else
                                 dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);