Merge pull request #9721 from smlng/pr/gnrc_udp/assert

gnrc_udp: assert ports not zero

sys/include/net/gnrc/udp.h

@@ -76,6 +76,8 @@ int gnrc_udp_calc_csum(gnrc_pktsnip_t *hdr, gnrc_pktsnip_t *pseudo_hdr);
  * @return  pointer to the newly created (and allocated) header
  * @return  NULL on `src == NULL`, `dst == NULL`, `src_len != 2`, `dst_len != 2`
  *          or on allocation error
+ *
+ * @pre     `src > 0` and `dst > 0`
  */
 gnrc_pktsnip_t *gnrc_udp_hdr_build(gnrc_pktsnip_t *payload, uint16_t src,
                                    uint16_t dst);

sys/net/gnrc/transport_layer/udp/gnrc_udp.c

@@ -280,6 +280,8 @@ int gnrc_udp_calc_csum(gnrc_pktsnip_t *hdr, gnrc_pktsnip_t *pseudo_hdr)
 gnrc_pktsnip_t *gnrc_udp_hdr_build(gnrc_pktsnip_t *payload, uint16_t src,
                                    uint16_t dst)
 {
+    assert((src > 0) && (dst > 0));
+
     gnrc_pktsnip_t *res;
     udp_hdr_t *hdr;