fix(mdns): add the maximum number of services

* Original commit: espressif/esp-idf@ba458c6

Author: lhespress

components/mdns/Kconfig

@@ -0,0 +1,13 @@
+menu "mDNS"
+
+config MDNS_MAX_SERVICES
+    int "Max number of services"
+    range 1 64
+    default 10
+    help
+        Services take up a certain amount of memory, and allowing fewer
+        services to be open at the same time conserves memory. Specify
+        the maximum amount of services here. The valid value is from 1
+        to 64.
+        
+endmenu

components/mdns/mdns.c

@@ -96,6 +96,21 @@ static mdns_srv_item_t * _mdns_get_service_item(const char * service, const char
     return NULL;
 }
 
+static bool _mdns_can_add_more_services(void)
+{
+    mdns_srv_item_t * s = _mdns_server->services;
+    uint16_t service_num = 0;
+    while (s) {
+        service_num ++;
+        s = s->next;
+        if (service_num >= MDNS_MAX_SERVICES) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 esp_err_t _mdns_send_rx_action(mdns_rx_packet_t * packet)
 {
     mdns_action_t * action = NULL;
@@ -4124,6 +4139,11 @@ esp_err_t mdns_service_add(const char * instance, const char * service, const ch
     if (!_mdns_server || _str_null_or_empty(service) || _str_null_or_empty(proto) || !port) {
         return ESP_ERR_INVALID_ARG;
     }
+
+    if (!_mdns_can_add_more_services()) {
+        return ESP_ERR_NO_MEM;
+    }
+
     mdns_srv_item_t * item = _mdns_get_service_item(service, proto);
     if (item) {
         return ESP_ERR_INVALID_ARG;

components/mdns/private_include/mdns_private.h

@@ -20,6 +20,9 @@
 #define _mdns_dbg_printf(...) printf(__VA_ARGS__)
 #endif
 
+/** The maximum number of services */
+#define MDNS_MAX_SERVICES           CONFIG_MDNS_MAX_SERVICES
+
 #define MDNS_ANSWER_PTR_TTL         4500
 #define MDNS_ANSWER_TXT_TTL         4500
 #define MDNS_ANSWER_SRV_TTL         120