Merge branch 'bugfix/mdns_configure_strict_mode' into 'master'

mdns: Fix mdns to correctly answer non-strict queries (+ additional fixes)

Closes IDF-2928, WIFI-3107, and IDFGH-4797

See merge request espressif/esp-idf!12645

components/mdns/Kconfig

@@ -56,6 +56,17 @@ menu "mDNS"
             Configures timeout for adding a new mDNS service. Adding a service
             fails if could not be completed within this time.
 
+    config MDNS_STRICT_MODE
+        bool "mDNS strict mode"
+        default "n"
+        help
+            Configures strict mode. Set this to 1 for the mDNS library to strictly follow the RFC6762:
+            Currently the only strict feature: Do not repeat original questions in response packets
+            (defined in RFC6762 sec. 6).
+            Default configuration is 0, i.e. non-strict mode, since some implementations,
+            such as lwIP mdns resolver (used by standard POSIX API like getaddrinfo, gethostbyname)
+            could not correctly resolve advertised names.
+
     config MDNS_TIMER_PERIOD_MS
         int "mDNS timer period (ms)"
         range 10 10000

components/mdns/mdns.c

@@ -2679,7 +2679,7 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
     }
 
     //if we have not set the hostname, we can not answer questions
-    if (header.questions && _str_null_or_empty(_mdns_server->hostname)) {
+    if (header.questions && !header.answers && _str_null_or_empty(_mdns_server->hostname)) {
         free(parsed_packet);
         return;
     }
@@ -2815,13 +2815,12 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
 
             if (parsed_packet->discovery && _mdns_name_is_discovery(name, type)) {
                 discovery = true;
-            } else {
-                if (!name->sub && _mdns_name_is_ours(name)) {
-                    ours = true;
-                    if (name->service && name->service[0] && name->proto && name->proto[0]) {
-                        service = _mdns_get_service_item(name->service, name->proto);
-                    }
+            } else if (!name->sub && _mdns_name_is_ours(name)) {
+                ours = true;
+                if (name->service && name->service[0] && name->proto && name->proto[0]) {
+                    service = _mdns_get_service_item(name->service, name->proto);
                 }
+            } else {
                 if (!parsed_packet->authoritative || record_type == MDNS_NS) {
                     //skip this record
                     continue;

components/mdns/mdns_networking.c

@@ -38,7 +38,7 @@ static esp_err_t _udp_pcb_main_init(void)
         _pcb_main = NULL;
         return ESP_ERR_INVALID_STATE;
     }
-    _pcb_main->mcast_ttl = 1;
+    _pcb_main->mcast_ttl = 255;
     _pcb_main->remote_port = MDNS_SERVICE_PORT;
     ip_addr_copy(_pcb_main->remote_ip, *(IP_ANY_TYPE));
     udp_recv(_pcb_main, &_udp_recv, _mdns_server);

components/mdns/private_include/mdns_private.h

@@ -32,7 +32,11 @@
  * such as lwIP mdns resolver (used by standard POSIX API like getaddrinfo, gethostbyname)
  * could not correctly resolve advertised names.
  */
+#ifndef CONFIG_MDNS_STRICT_MODE
 #define MDNS_STRICT_MODE 0
+#else
+#define MDNS_STRICT_MODE 1
+#endif
 
 #if !MDNS_STRICT_MODE
 /* mDNS responders sometimes repeat queries in responses