fix(mdns): Remove strict mode as it's invalid

Strict mode was introduced to support "one-shot" queries (described in
RFC6762/sec5.1) that are sent by lwip or dig. It was incorrectly assumed
that responding to such queries violates the spec, as we have to repeat
queries in responces, which is forbidden in RFC6762/sec6. It is however
required to repeat query fields according to the Section 6.7. Legacy
Unicast Responses: "it MUST repeat the query ID and the question
given in the query message."

Author: david-cermak

components/mdns/Kconfig

@@ -64,17 +64,6 @@ 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

@@ -1728,7 +1728,6 @@ static void _mdns_create_answer_from_parsed_packet(mdns_parsed_packet_t *parsed_
             return;
         }
 
-#ifdef MDNS_REPEAT_QUERY_IN_RESPONSE
         if (parsed_packet->src_port != MDNS_SERVICE_PORT &&  // Repeat the queries only for "One-Shot mDNS queries"
                 (q->type == MDNS_TYPE_ANY || q->type == MDNS_TYPE_A || q->type == MDNS_TYPE_AAAA)) {
             mdns_out_question_t *out_question = malloc(sizeof(mdns_out_question_t));
@@ -1751,7 +1750,6 @@ static void _mdns_create_answer_from_parsed_packet(mdns_parsed_packet_t *parsed_
             out_question->own_dynamic_memory = true;
             queueToEnd(mdns_out_question_t, packet->questions, out_question);
         }
-#endif // MDNS_REPEAT_QUERY_IN_RESPONSE
         if (q->unicast) {
             unicast = true;
         }

components/mdns/private_include/mdns_private.h

@@ -21,27 +21,6 @@
 #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.
- */
-#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
- * but according to RFC6762, sec 6: Responses MUST NOT contain
- * any item in question field */
-#define  MDNS_REPEAT_QUERY_IN_RESPONSE 1
-#endif
-
 /** Number of predefined interfaces */
 #ifndef CONFIG_MDNS_PREDEF_NETIF_STA
 #define CONFIG_MDNS_PREDEF_NETIF_STA 0