edns: set EXT-RCODE correctly

fixes #282

src/knot/nameserver/process_query.c

@@ -314,6 +314,12 @@ static int answer_edns_put(knot_pkt_t *resp, struct query_data *qdata)
 		return KNOT_EOK;
 	}
 
+	/* Write back extended RCODE. */
+	if (qdata->rcode_ext != 0) {
+		knot_wire_set_rcode(resp->wire, KNOT_EDNS_RCODE_LO(qdata->rcode_ext));
+		knot_edns_set_ext_rcode(&qdata->opt_rr, KNOT_EDNS_RCODE_HI(qdata->rcode_ext));
+	}
+
 	/* Reclaim reserved size. */
 	int ret = knot_pkt_reclaim(resp, knot_edns_wire_size(&qdata->opt_rr));
 	if (ret != KNOT_EOK) {

src/libknot/rrtype/opt.h

@@ -56,9 +56,15 @@ enum knot_edns_const {
 	/*! \brief NSID option code. */
 	KNOT_EDNS_OPTION_NSID          = 3,
 	/*! \brief EDNS client subnet option code. */
-	KNOT_EDNS_OPTION_CLIENT_SUBNET = 8
+	KNOT_EDNS_OPTION_CLIENT_SUBNET = 8,
+	/*! \brief Extended RCODE BADVERS. */
+	KNOT_EDNS_RCODE_BADVERS = 16,
 };
 
+/* Helpers for splitting extended RCODE. */
+#define KNOT_EDNS_RCODE_HI(rc) (rc >> 4)
+#define KNOT_EDNS_RCODE_LO(rc) (rc & 0x000f)
+
 /*!
  * \brief EDNS DO flag.
  *
@@ -67,10 +73,6 @@ enum knot_edns_const {
  */
 static const uint16_t KNOT_EDNS_FLAG_DO = (uint16_t)1 << 15;
 
-/*! \brief Extended RCODE BADVERS. */
-static const uint8_t KNOT_EDNS_RCODE_BADVERS = 16;
-
-
 /*----------------------------------------------------------------------------*/
 /* EDNS OPT RR handling functions.                                            */
 /*----------------------------------------------------------------------------*/