internet: solve DS query bellow a delegation point as a delegation

src/knot/nameserver/internet.c

@@ -358,10 +358,10 @@ static int name_found(knot_pkt_t *pkt, knotd_qdata_t *qdata)
 		return follow_cname(pkt, KNOT_RRTYPE_CNAME, qdata);
 	}
 
-	/* DS query is answered normally, but everything else at/below DP
+	/* DS query at DP is answered normally, but everything else at/below DP
 	 * triggers referral response. */
-	if (qtype != KNOT_RRTYPE_DS &&
-	    ((qdata->extra->node->flags & NODE_FLAGS_DELEG) || qdata->extra->node->flags & NODE_FLAGS_NONAUTH)) {
+	if (((qdata->extra->node->flags & NODE_FLAGS_DELEG) && qtype != KNOT_RRTYPE_DS) ||
+	    (qdata->extra->node->flags & NODE_FLAGS_NONAUTH)) {
 		return KNOTD_IN_STATE_DELEG;
 	}
 

tests-extra/data/flags.zone

@@ -69,6 +69,10 @@ f.dname-tree	DNAME	dname-tree
 
 dname-out	DNAME	outside.zone.
 
+; DS tests
+ds-sub		NS	dns.net.ds-sub
+dns.net.ds-sub	A	1.1.1.1
+
 ; Fourth level domain with A record
 fourth.third.second A	1.1.1.1
 

tests-extra/tests/basic/query/test.py

@@ -61,6 +61,16 @@ resp = knot.dig("bellow.ns.sub.flags", "A", udp=True)
 resp.check(rcode="NOERROR", flags="QR", noflags="AA TC AD RA")
 resp.cmp(bind, additional=True)
 
+# Positive (NODATA, at delegation, DS type)
+resp = knot.dig("ds-sub.flags", "DS", udp=True)
+resp.check(rcode="NOERROR", flags="QR AA", noflags="TC AD RA")
+resp.cmp(bind, additional=True)
+
+# Positive (REFERRAL, below delegation, DS type)
+resp = knot.dig("net.ds-sub.flags", "DS", udp=True)
+resp.check(rcode="NOERROR", flags="QR", noflags="AA TC AD RA")
+resp.cmp(bind, additional=True)
+
 ''' ANY query type. '''
 
 # ANY to SOA record