fix(examples): Make multi-netif example working with DNS_PER_DEFAULT_NETIF feature

Author: david-cermak

examples/esp_netif/multiple_netifs/README.md

@@ -19,6 +19,14 @@ This example demonstrates working with multiple different interfaces with differ
   * It tries to reconfigure DNS server if host name resolution fails
   * It tries to manually change the default interface if connection fails
 
+### Handling DNS server across interfaces
+
+This example also demonstrates how DNS servers could be handled on network interface level, as lwIP used global DNS server information.
+
+All network interfaces store their DNS info upon acquiring an IP in the internal structure (in the application code) and the DNS servers are restored if host name resolution fails.
+
+This functionality is handled in IDF (supported from v5.3) automatically if `CONFIG_ESP_NETIF_SET_DNS_PER_DEFAULT_NETIF` is enabled, the DNS server info keeps updating per network interface in IDF layers. This examples uses the IDF functionality if `CONFIG_ESP_NETIF_SET_DNS_PER_DEFAULT_NETIF=1`.
+
 ### Hardware Required
 
 To run this example, it's recommended that you have an official ESP32 Ethernet development board - [ESP32-Ethernet-Kit](https://docs.espressif.com/projects/esp-idf/en/latest/hw-reference/get-started-ethernet-kit.html).

examples/esp_netif/multiple_netifs/main/Kconfig.projbuild

@@ -54,4 +54,14 @@ menu "Example Configuration"
             bool "Using simple UART-PPP driver"
     endchoice
 
+    config EXAMPLE_DEMONSTRATE_DNS_CLEAR_CACHE
+        bool "Run DNS clear cache"
+        default n
+        help
+            This example will cleanup the DNS cache
+            every iteration of the demo network operation.
+            This forces the TCP/IP stack to always resolve DNS names,
+            thus exercising potentially invalid DNS configuration.
+            Set this to "y" for testing, but keep as "n" for production.
+
 endmenu

examples/esp_netif/multiple_netifs/main/ethernet_connect.c

@@ -95,7 +95,7 @@ static void eth_destroy(iface_info_t *info)
     free(eth_info);
 }
 
-iface_info_t *eth_init(int prio)
+iface_info_t *example_eth_init(int prio)
 {
     struct eth_info_t *eth_info = malloc(sizeof(struct eth_info_t));
     assert(eth_info);
@@ -124,7 +124,7 @@ iface_info_t *eth_init(int prio)
     eth_info->parent.netif = esp_netif_new(&cfg);
     eth_info->glue = esp_eth_new_netif_glue(eth_info->eth_handle);
     // Attach Ethernet driver to TCP/IP stack
-    ESP_ERROR_CHECK(esp_netif_attach(eth_info->parent.netif, eth_info->glue ));
+    ESP_ERROR_CHECK(esp_netif_attach(eth_info->parent.netif, eth_info->glue));
 
     // Register user defined event handers
     ESP_ERROR_CHECK(esp_event_handler_register(ETH_EVENT, ESP_EVENT_ANY_ID, &eth_event_handler, eth_info));

examples/esp_netif/multiple_netifs/main/multi_netif_main.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2023-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Unlicense OR CC0-1.0
  */
@@ -23,9 +23,9 @@
 #include "nvs_flash.h"
 #include "iface_info.h"
 
-iface_info_t *eth_init(int prio);
-iface_info_t *wifi_init(int prio);
-iface_info_t *ppp_init(int prio);
+iface_info_t *example_eth_init(int prio);
+iface_info_t *example_wifi_init(int prio);
+iface_info_t *example_ppp_init(int prio);
 esp_err_t check_connectivity(const char *host);
 
 #define HOST        "www.espressif.com"
@@ -69,14 +69,18 @@ void app_main(void)
 
     // all interfaces
     iface_info_t *ifaces[] = {
-        eth_init(ETH_PRIO),
-        wifi_init(WIFI_PRIO),
-        ppp_init(PPP_PRIO),
+        example_eth_init(ETH_PRIO),
+        example_wifi_init(WIFI_PRIO),
+        example_ppp_init(PPP_PRIO),
     };
     size_t num_of_ifaces = sizeof(ifaces) / sizeof(ifaces[0]);
 
     while (true) {
+#ifdef CONFIG_EXAMPLE_DEMONSTRATE_DNS_CLEAR_CACHE
+        // For demonstration purposes we clear DNS table every iteration to exercise
+        // a condition of DNS servers being misconfigured
         dns_clear_cache();
+#endif
         vTaskDelay(pdMS_TO_TICKS(2000));
         ssize_t i = get_default(ifaces, num_of_ifaces);
         if (i == -1) {  // default netif is NULL, probably all interfaces are down -> retry
@@ -91,7 +95,9 @@ void app_main(void)
             continue;
         }
         if (connect_status == ESP_ERR_NOT_FOUND) {
+#ifndef CONFIG_ESP_NETIF_SET_DNS_PER_DEFAULT_NETIF
             // set the default DNS info to global DNS server list
+            // manually if DNS_PER_DEFAULT_NETIF if OFF or not-supported
             for (int j = 0; j < 2; ++j) {
                 esp_netif_dns_info_t dns_info;
                 esp_netif_get_dns_info(ifaces[i]->netif, j, &dns_info);
@@ -102,6 +108,12 @@ void app_main(void)
                     ESP_LOGI(TAG, "Reconfigured DNS%i=" IPSTR, j, IP2STR(&ifaces[i]->dns[j].ip.u_addr.ip4));
                 }
             }
+#else
+            // simulate that the (default) netif is brought UP
+            // this is only needed, since we explicitly clear DNS servers every iteration using dns_clear_cache()
+            // (for demonstration purpose only, won't be needed in your project, unless you delete DNS info for some reasons)
+            esp_netif_action_connected(ifaces[i]->netif, NULL, 0, NULL);
+#endif
         }
         if (connect_status == ESP_FAIL) {
             ESP_LOGE(TAG, "No connection via the default netif!");

examples/esp_netif/multiple_netifs/main/ppp_connect.c

@@ -85,7 +85,7 @@ static void ppp_destroy(iface_info_t *info)
     free(info);
 }
 
-iface_info_t *init_ppp(int prio)
+iface_info_t *example_ppp_init(int prio)
 {
     struct ppp_info_t *ppp_info = calloc(1, sizeof(struct ppp_info_t));
     assert(ppp_info);

examples/esp_netif/multiple_netifs/main/wifi_connect.c

@@ -75,7 +75,7 @@ static void wifi_destroy(iface_info_t *info)
     free(info);
 }
 
-iface_info_t *wifi_init(int prio)
+iface_info_t *example_wifi_init(int prio)
 {
     struct iface_info_t *wifi_info = malloc(sizeof(iface_info_t));
     assert(wifi_info);
@@ -100,9 +100,9 @@ iface_info_t *wifi_init(int prio)
             .password = CONFIG_ESP_WIFI_PASSWORD,
         },
     };
-    ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_STA) );
-    ESP_ERROR_CHECK(esp_wifi_set_config(WIFI_IF_STA, &wifi_config) );
-    ESP_ERROR_CHECK(esp_wifi_start() );
+    ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_STA));
+    ESP_ERROR_CHECK(esp_wifi_set_config(WIFI_IF_STA, &wifi_config));
+    ESP_ERROR_CHECK(esp_wifi_start());
 
     ESP_LOGI(TAG, "wifi_init_sta finished.");
 

examples/esp_netif/multiple_netifs/sdkconfig.defaults

@@ -1,2 +1,5 @@
+# You can use CONFIG_ESP_NETIF_SET_DNS_PER_DEFAULT_NETIF
+# to perform DNS server updates automatically in esp_netif layers
+# instead of manually as it is demonstrated in this example
 CONFIG_LWIP_PPP_SUPPORT=y
 CONFIG_LWIP_PPP_NOTIFY_PHASE_SUPPORT=y