fix(esp_netif): Prevent running esp_netif_sntp_init() multiple times

Closes https://github.com/espressif/esp-idf/issues/12854

components/esp_netif/lwip/esp_netif_sntp.c

@@ -91,6 +91,7 @@ void esp_netif_sntp_renew_servers(void *handler_args, esp_event_base_t base, int
 esp_err_t esp_netif_sntp_init(const esp_sntp_config_t * config)
 {
     esp_err_t ret = ESP_OK;
+    ESP_RETURN_ON_FALSE(s_storage == NULL, ESP_ERR_INVALID_STATE, TAG, "esp_netif_sntp already initialized");
     s_storage = calloc(1, sizeof(sntp_storage_t) + // allocate space for servers only if we are supposed to refresh the settings
                           (config->renew_servers_after_new_IP ? config->num_of_servers * sizeof(char*) : 0));
     ESP_GOTO_ON_FALSE(s_storage != NULL, ESP_ERR_NO_MEM, err, TAG, "Failed to allocate SNTP storage");

components/esp_netif/test_apps/test_app_esp_netif/main/esp_netif_test.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2022-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2022-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Unlicense OR CC0-1.0
  */
@@ -48,7 +48,15 @@ TEST(esp_netif, init_and_destroy_sntp)
 {
     esp_sntp_config_t config = ESP_NETIF_SNTP_DEFAULT_CONFIG("127.0.0.1");
     config.start = false;
-    esp_netif_sntp_init(&config);
+    TEST_ESP_OK(esp_netif_sntp_init(&config));
+    // Cannot initialize multiple times
+    TEST_ASSERT_NOT_EQUAL(ESP_OK, esp_netif_sntp_init(&config));
+    // Try again to see that the state didn't change
+    TEST_ASSERT_NOT_EQUAL(ESP_OK, esp_netif_sntp_init(&config));
+    esp_netif_sntp_deinit();
+
+    // Can initialize again once it's destroyed
+    TEST_ESP_OK(esp_netif_sntp_init(&config));
     esp_netif_sntp_deinit();
 }
 

docs/en/api-reference/network/esp_netif.rst

@@ -264,7 +264,7 @@ You can find a brief introduction to SNTP in general, its initialization code, a
 
 This section provides more details about specific use cases of the SNTP service, with statically configured servers, or use the DHCP-provided servers, or both. The workflow is usually very simple:
 
-1) Initialize and configure the service using :cpp:func:`esp_netif_sntp_init()`.
+1) Initialize and configure the service using :cpp:func:`esp_netif_sntp_init()`. This operations can only be called once (unless the SNTP service has been destroyed by :cpp:func:`esp_netif_sntp_deinit()`)
 2) Start the service via :cpp:func:`esp_netif_sntp_start()`. This step is not needed if we auto-started the service in the previous step (default). It is useful to start the service explicitly after connecting if we want to use the DHCP-obtained NTP servers. Please note, this option needs to be enabled before connecting, but the SNTP service should be started after.
 3) Wait for the system time to synchronize using :cpp:func:`esp_netif_sntp_sync_wait()` (only if needed).
 4) Stop and destroy the service using :cpp:func:`esp_netif_sntp_deinit()`.

docs/zh_CN/api-reference/network/esp_netif.rst

@@ -264,7 +264,7 @@ SNTP 的简要介绍、初始化代码和基本模式请参阅 :doc:`系统时
 
 本节介绍了使用 SNTP 服务特定用例的详细信息，包括静态配置的服务器、使用 DHCP 提供的服务器或两者兼备的情况，操作流程如下：
 
-1) 调用 :cpp:func:`esp_netif_sntp_init()` 初始化服务并完成配置。
+1) 调用 :cpp:func:`esp_netif_sntp_init()` 初始化服务并完成配置。此操作只能执行一次（除非已调用 :cpp:func:`esp_netif_sntp_deinit()` 销毁 SNTP 服务）。
 2) 调用 :cpp:func:`esp_netif_sntp_start()` 启动服务。如果在前一步中已经默认启动了服务，则不需要此步骤。如果需使用通过 DHCP 获取的 NTP 服务器，推荐在完成连接后显式启动该服务。注意，应在连接前启用通过 DHCP 获取的 NTP 服务器选项，并在连接后再启用 SNTP 服务。
 3) 需要时，可调用 :cpp:func:`esp_netif_sntp_sync_wait()` 等待系统时间同步。
 4) 调用 :cpp:func:`esp_netif_sntp_deinit()` 停止并销毁服务。