mdns: Support queries in responses in mDNS non-strict mode

By default adds original queries to responses in order to be resolved by some resolvers, such as lwIP mdns library. This functionality however is discouraged by the RFC6762, so it could be disabled in menuconfig if MDNS_STRICT_MODE configured

Closes https://github.com/espressif/esp-idf/issues/5521

components/mdns/mdns.c

@@ -1313,6 +1313,17 @@ static void _mdns_create_answer_from_parsed_packet(mdns_parsed_packet_t * parsed
                     _mdns_free_tx_packet(packet);
                     return;
                 }
+#ifdef MDNS_REPEAT_QUERY_IN_RESPONSE
+                mdns_out_question_t * out_question = malloc(sizeof(mdns_out_question_t));
+                if (out_question == NULL) {
+                    HOOK_MALLOC_FAILED;
+                    _mdns_free_tx_packet(packet);
+                    return;
+                }
+                memcpy(out_question, q, sizeof(mdns_out_question_t));
+                out_question->next = NULL;
+                queueToEnd(mdns_out_question_t, packet->questions, out_question);
+#endif // MDNS_REPEAT_QUERY_IN_RESPONSE
             } else if (!_mdns_alloc_answer(&packet->answers, q->type, NULL, send_flush, false)) {
                 _mdns_free_tx_packet(packet);
                 return;

components/mdns/private_include/mdns_private.h

@@ -23,6 +23,22 @@
 #define _mdns_dbg_printf(...) printf(__VA_ARGS__)
 #endif
 
+/** mDNS strict mode: Set this to 1 for the mDNS library to strictly follow the RFC6762:
+ * Strict features:
+ *   - to do not set original questions in response packets per RFC6762, sec 6
+ *
+ * The actual 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.
+ */
+#define MDNS_STRICT_MODE 0
+
+#if !MDNS_STRICT_MODE
+/* mDNS responders sometimes repeat queries in responses
+ * but according to RFC6762, sec 6: Responses MUST NOT contain
+ * any item in question field */
+#define  MDNS_REPEAT_QUERY_IN_RESPONSE 1
+#endif
 /** The maximum number of services */
 #define MDNS_MAX_SERVICES           CONFIG_MDNS_MAX_SERVICES