dns: don't relaunch query on CNAMEs.

The recursive resolver is supposed to do that for us.

(note, the old code already didn't relaunch it, but the intention was
to make it do that)

src/socket/dns.rs

@@ -330,16 +330,15 @@ impl<'a> DnsSocket<'a> {
                         }
                         RecordData::Cname(name) => {
                             net_trace!("CNAME: {:?}", name);
-                            copy_name(&mut pq.name, p.parse_name(name))?;
-
-                            // Relaunch query with the new name.
-                            // If the server has bundled A records for the CNAME in the same packet,
-                            // we'll process them in next iterations, and cancel the query relaunch.
-                            pq.retransmit_at = Instant::ZERO;
-                            pq.delay = RETRANSMIT_DELAY;
 
-                            pq.txid = cx.rand().rand_u16();
-                            pq.port = cx.rand().rand_source_port();
+                            // When faced with a CNAME, recursive resolvers are supposed to
+                            // resolve the CNAME and append the results for it.
+                            //
+                            // We update the query with the new name, so that we pick up the A/AAAA
+                            // records for the CNAME when we parse them later.
+                            // I believe it's mandatory the CNAME results MUST come *after* in the
+                            // packet, so it's enough to do one linear pass over it.
+                            copy_name(&mut pq.name, p.parse_name(name))?;
                         }
                         RecordData::Other(type_, data) => {
                             net_trace!("unknown: {:?} {:?}", type_, data)
@@ -347,10 +346,10 @@ impl<'a> DnsSocket<'a> {
                     }
                 }
 
-                if !addresses.is_empty() {
-                    q.state = State::Completed(CompletedQuery { addresses })
-                } else {
+                if addresses.is_empty() {
                     q.state = State::Failure;
+                } else {
+                    q.state = State::Completed(CompletedQuery { addresses })
                 }
 
                 // If we get here, packet matched the current query, stop processing.