fix(esp_netif): Add API docs to DHCP client/server operations

components/esp_netif/include/esp_netif.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2019-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2019-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -594,6 +594,23 @@ esp_err_t esp_netif_napt_disable(esp_netif_t *esp_netif);
 /**
  * @brief  Set or Get DHCP server option
  *
+ * @note Please note that not all combinations of identifiers and options are supported.
+ * Get operations:
+ *  * IP_ADDRESS_LEASE_TIME
+ *  * ESP_NETIF_SUBNET_MASK/REQUESTED_IP_ADDRESS (both options do the same, they reflect dhcps_lease_t)
+ *  * ROUTER_SOLICITATION_ADDRESS
+ *  * DOMAIN_NAME_SERVER
+ * Set operations:
+ *  * IP_ADDRESS_LEASE_TIME
+ *  * ESP_NETIF_SUBNET_MASK -- set operation is allowed only if the configured mask corresponds to the settings,
+ *                             if not, please use esp_netif_set_ip_info() to prevent misconfiguration of DHCPS.
+ *  * REQUESTED_IP_ADDRESS -- if the address pool is enabled, a sanity check for start/end addresses is performed
+ *                             before setting.
+ *  * ROUTER_SOLICITATION_ADDRESS
+ *  * DOMAIN_NAME_SERVER
+ *  * ESP_NETIF_CAPTIVEPORTAL_URI -- set operation copies the pointer to the URI, so it is owned by the application
+ *                                    and needs to be maintained valid throughout the entire DHCP Server lifetime.
+ *
  * @param[in]  esp_netif Handle to esp-netif instance
  * @param[in] opt_op ESP_NETIF_OP_SET to set an option, ESP_NETIF_OP_GET to get an option.
  * @param[in] opt_id Option index to get or set, must be one of the supported enum values.
@@ -613,6 +630,16 @@ esp_netif_dhcps_option(esp_netif_t *esp_netif, esp_netif_dhcp_option_mode_t opt_
 /**
  * @brief  Set or Get DHCP client option
  *
+ * @note Please note that not all combinations of identifiers and options are supported.
+ * Get operations:
+ *  * ESP_NETIF_IP_REQUEST_RETRY_TIME
+ *  * ESP_NETIF_VENDOR_SPECIFIC_INFO -- only available if ESP_DHCP_DISABLE_VENDOR_CLASS_IDENTIFIER=n
+ * Set operations:
+ *  * ESP_NETIF_IP_REQUEST_RETRY_TIME
+ *  * ESP_NETIF_VENDOR_SPECIFIC_INFO -- only available if ESP_DHCP_DISABLE_VENDOR_CLASS_IDENTIFIER=n
+ *                                      lwip layer creates its own copy of the supplied identifier.
+ *                                      (the internal copy could be feed by calling dhcp_free_vendor_class_identifier())
+ *
  * @param[in]  esp_netif Handle to esp-netif instance
  * @param[in] opt_op ESP_NETIF_OP_SET to set an option, ESP_NETIF_OP_GET to get an option.
  * @param[in] opt_id Option index to get or set, must be one of the supported enum values.

examples/protocols/http_server/captive_portal/README.md

@@ -126,4 +126,4 @@ Note `URL (114)` with the AP address.
 	    URL (114), length 18: "http://192.168.4.1"
 	    Router-Discovery (31), length 1: N
 	    Vendor-Option (43), length 6: 1.4.0.0.0.2
-```
+```

examples/protocols/http_server/captive_portal/main/main.c

@@ -24,7 +24,6 @@
 #define EXAMPLE_ESP_WIFI_SSID CONFIG_ESP_WIFI_SSID
 #define EXAMPLE_ESP_WIFI_PASS CONFIG_ESP_WIFI_PASSWORD
 #define EXAMPLE_MAX_STA_CONN CONFIG_ESP_MAX_STA_CONN
-#define EXAMPLE_ENABLE_DHCP_CAPTIVEPORTAL_URI CONFIG_ESP_ENABLE_DHCP_CAPTIVEPORTAL
 
 extern const char root_start[] asm("_binary_root_html_start");
 extern const char root_end[] asm("_binary_root_html_end");
@@ -80,6 +79,7 @@ static void wifi_init_softap(void)
              EXAMPLE_ESP_WIFI_SSID, EXAMPLE_ESP_WIFI_PASS);
 }
 
+#ifdef CONFIG_ESP_ENABLE_DHCP_CAPTIVEPORTAL
 static void dhcp_set_captiveportal_url(void) {
     // get the IP of the access point to redirect to
     esp_netif_ip_info_t ip_info;
@@ -91,6 +91,7 @@ static void dhcp_set_captiveportal_url(void) {
 
     // turn the IP into a URI
     char* captiveportal_uri = (char*) malloc(32 * sizeof(char));
+    assert(captiveportal_uri && "Failed to allocate captiveportal_uri");
     strcpy(captiveportal_uri, "http://");
     strcat(captiveportal_uri, ip_addr);
 
@@ -102,6 +103,7 @@ static void dhcp_set_captiveportal_url(void) {
     ESP_ERROR_CHECK(esp_netif_dhcps_option(netif, ESP_NETIF_OP_SET, ESP_NETIF_CAPTIVEPORTAL_URI, captiveportal_uri, strlen(captiveportal_uri)));
     ESP_ERROR_CHECK_WITHOUT_ABORT(esp_netif_dhcps_start(netif));
 }
+#endif // CONFIG_ESP_ENABLE_DHCP_CAPTIVEPORTAL
 
 // HTTP GET Handler
 static esp_err_t root_get_handler(httpd_req_t *req)
@@ -180,7 +182,7 @@ void app_main(void)
     wifi_init_softap();
 
     // Configure DNS-based captive portal, if configured
-    #if CONFIG_ESP_ENABLE_DHCP_CAPTIVEPORTAL
+    #ifdef CONFIG_ESP_ENABLE_DHCP_CAPTIVEPORTAL
         dhcp_set_captiveportal_url();
     #endif