Merge branch 'bugfix/udp_multicast_example_errors' into 'master'

udp_multicast_example: better handling wrong addresses

Closes IDFGH-979

See merge request idf/esp-idf!4784

examples/protocols/sockets/udp_multicast/main/udp_multicast_example_main.c

@@ -74,6 +74,8 @@ static int socket_add_ipv4_multicast_group(int sock, bool assign_source_if)
     err = inet_aton(MULTICAST_IPV4_ADDR, &imreq.imr_multiaddr.s_addr);
     if (err != 1) {
         ESP_LOGE(V4TAG, "Configured IPV4 multicast address '%s' is invalid.", MULTICAST_IPV4_ADDR);
+        // Errors in the return value have to be negative
+        err = -1;
         goto err;
     }
     ESP_LOGI(TAG, "Configured IPV4 Multicast address %s", inet_ntoa(imreq.imr_multiaddr.s_addr));
@@ -426,6 +428,10 @@ static void mcast_example_task(void *pvParameters)
                     ESP_LOGE(TAG, "getaddrinfo() failed for IPV4 destination address. error: %d", err);
                     break;
                 }
+                if (res == 0) {
+                    ESP_LOGE(TAG, "getaddrinfo() did not return any addresses");
+                    break;
+                }
 #ifdef CONFIG_EXAMPLE_IPV4_ONLY
                 ((struct sockaddr_in *)res->ai_addr)->sin_port = htons(UDP_PORT);
                 inet_ntoa_r(((struct sockaddr_in *)res->ai_addr)->sin_addr, addrbuf, sizeof(addrbuf)-1);