mdns: fix bit order issue in DNS header flags

The bit field in the header flags does not match its intended order on
little endian machines. The PR removes the bit field and uses bit
operations instead.

Author: gjc13

components/mdns/mdns.c

@@ -1686,7 +1686,7 @@ static void _mdns_create_answer_from_parsed_packet(mdns_parsed_packet_t *parsed_
     if (!packet) {
         return;
     }
-    packet->flags = MDNS_FLAGS_AUTHORITATIVE;
+    packet->flags = MDNS_FLAGS_QR_AUTHORITATIVE;
     packet->distributed = parsed_packet->distributed;
     packet->id = parsed_packet->id;
 
@@ -1935,7 +1935,7 @@ static mdns_tx_packet_t * _mdns_create_announce_packet(mdns_if_t tcpip_if, mdns_
     if (!packet) {
         return NULL;
     }
-    packet->flags = MDNS_FLAGS_AUTHORITATIVE;
+    packet->flags = MDNS_FLAGS_QR_AUTHORITATIVE;
 
     uint8_t i;
     for (i=0; i<len; i++) {
@@ -1965,7 +1965,7 @@ static mdns_tx_packet_t * _mdns_create_announce_from_probe(mdns_tx_packet_t * pr
     if (!packet) {
         return NULL;
     }
-    packet->flags = MDNS_FLAGS_AUTHORITATIVE;
+    packet->flags = MDNS_FLAGS_QR_AUTHORITATIVE;
 
     mdns_out_answer_t * s = probe->servers;
     while (s) {
@@ -2005,7 +2005,7 @@ static void _mdns_pcb_send_bye(mdns_if_t tcpip_if, mdns_ip_protocol_t ip_protoco
     if (!packet) {
         return;
     }
-    packet->flags = MDNS_FLAGS_AUTHORITATIVE;
+    packet->flags = MDNS_FLAGS_QR_AUTHORITATIVE;
     size_t i;
     for (i=0; i<len; i++) {
         if (!_mdns_alloc_answer(&packet->answers, MDNS_TYPE_PTR, services[i]->service, NULL, true, true)) {
@@ -3342,13 +3342,13 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
     memset(name, 0, sizeof(mdns_name_t));
 
     header.id = _mdns_read_u16(data, MDNS_HEAD_ID_OFFSET);
-    header.flags.value = _mdns_read_u16(data, MDNS_HEAD_FLAGS_OFFSET);
+    header.flags = _mdns_read_u16(data, MDNS_HEAD_FLAGS_OFFSET);
     header.questions = _mdns_read_u16(data, MDNS_HEAD_QUESTIONS_OFFSET);
     header.answers = _mdns_read_u16(data, MDNS_HEAD_ANSWERS_OFFSET);
     header.servers = _mdns_read_u16(data, MDNS_HEAD_SERVERS_OFFSET);
     header.additional = _mdns_read_u16(data, MDNS_HEAD_ADDITIONAL_OFFSET);
 
-    if (header.flags.value == MDNS_FLAGS_AUTHORITATIVE && packet->src_port != MDNS_SERVICE_PORT) {
+    if (header.flags == MDNS_FLAGS_QR_AUTHORITATIVE && packet->src_port != MDNS_SERVICE_PORT) {
         free(parsed_packet);
         return;
     }
@@ -3362,8 +3362,8 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
     parsed_packet->tcpip_if = packet->tcpip_if;
     parsed_packet->ip_protocol = packet->ip_protocol;
     parsed_packet->multicast = packet->multicast;
-    parsed_packet->authoritative = header.flags.value == MDNS_FLAGS_AUTHORITATIVE;
-    parsed_packet->distributed = header.flags.value == MDNS_FLAGS_DISTRIBUTED;
+    parsed_packet->authoritative = (header.flags == MDNS_FLAGS_QR_AUTHORITATIVE);
+    parsed_packet->distributed = header.flags == MDNS_FLAGS_DISTRIBUTED;
     parsed_packet->id = header.id;
     esp_netif_ip_addr_copy(&parsed_packet->src, &packet->src);
     parsed_packet->src_port = packet->src_port;
@@ -3499,7 +3499,7 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
                     service = _mdns_get_service_item(name->service, name->proto, NULL);
                 }
             } else {
-                if (!header.flags.qr || record_type == MDNS_NS) {
+                if ((header.flags & MDNS_FLAGS_QUERY_REPSONSE) == 0 || record_type == MDNS_NS) {
                     //skip this record
                     continue;
                 }
@@ -6075,11 +6075,11 @@ void mdns_debug_packet(const uint8_t * data, size_t len)
     header.additional = _mdns_read_u16(data, MDNS_HEAD_ADDITIONAL_OFFSET);
 
     _mdns_dbg_printf("%s",
-        (header.flags.value == MDNS_FLAGS_AUTHORITATIVE)?"AUTHORITATIVE\n":
+        (header.flags.value == MDNS_FLAGS_QR_AUTHORITATIVE)?"AUTHORITATIVE\n":
         (header.flags.value == MDNS_FLAGS_DISTRIBUTED)?"DISTRIBUTED\n":
         (header.flags.value == 0)?"\n":" "
     );
-    if (header.flags.value && header.flags.value != MDNS_FLAGS_AUTHORITATIVE) {
+    if (header.flags.value && header.flags.value != MDNS_FLAGS_QR_AUTHORITATIVE) {
         _mdns_dbg_printf("0x%04X\n", header.flags.value);
     }
 

components/mdns/private_include/mdns_private.h

@@ -71,7 +71,9 @@
 #define MDNS_ANSWER_A_TTL           120
 #define MDNS_ANSWER_AAAA_TTL        120
 
-#define MDNS_FLAGS_AUTHORITATIVE    0x8400
+#define MDNS_FLAGS_QUERY_REPSONSE   0x8000
+#define MDNS_FLAGS_AUTHORITATIVE    0x0400
+#define MDNS_FLAGS_QR_AUTHORITATIVE (MDNS_FLAGS_QUERY_REPSONSE | MDNS_FLAGS_AUTHORITATIVE)
 #define MDNS_FLAGS_DISTRIBUTED      0x0200
 
 #define MDNS_NAME_REF               0xC000
@@ -211,21 +213,7 @@ typedef enum {
 
 typedef struct {
     uint16_t id;
-    union {
-        struct {
-            uint16_t qr :1;
-            uint16_t opCode :4;
-            uint16_t aa :1;
-            uint16_t tc :1;
-            uint16_t rd :1;
-            uint16_t ra :1;
-            uint16_t z :1;
-            uint16_t ad :1;
-            uint16_t cd :1;
-            uint16_t rCode :4;//response/error code
-        };
-        uint16_t value;
-    } flags;
+    uint16_t flags;
     uint16_t questions; //QDCOUNT
     uint16_t answers;   //ANCOUNT
     uint16_t servers;   //NSCOUNT