feat(lwip): Add support for PPP server

Added support PPP_SERVER option in LWIP
Added support for configuring preferred addresses of PPP endpoints.

components/esp_netif/include/esp_netif_ppp.h

@@ -28,6 +28,10 @@ typedef struct esp_netif_ppp_config {
                                      *   The current session must be closed, settings will be applied upon connecting.
                                      *   */
 #endif // CONFIG_LWIP_ENABLE_LCP_ECHO
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    uint32_t ppp_our_ip4_addr;   /**< Set our preferred address, typically used when we're the PPP server */
+    uint32_t ppp_their_ip4_addr; /**< Set our preferred address, typically used when we're the PPP server */
+#endif // CONFIG_LWIP_PPP_SERVER_SUPPORT
 } esp_netif_ppp_config_t;
 
 /** @brief event id offset for PHASE related events

components/esp_netif/lwip/esp_netif_lwip_ppp.c

@@ -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
  */
@@ -33,6 +33,10 @@ typedef struct lwip_peer2peer_ctx {
     bool ppp_error_event_enabled;
 #ifdef CONFIG_LWIP_ENABLE_LCP_ECHO
     bool ppp_lcp_echo_disabled;
+#endif
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    uint32_t ppp_our_ip4_addr;      // our desired IP (0 if no preference)
+    uint32_t ppp_their_ip4_addr;    // their desired IP (0 if no preference)
 #endif
     ppp_pcb *ppp;
 } lwip_peer2peer_ctx_t;
@@ -246,9 +250,25 @@ esp_err_t esp_netif_start_ppp(esp_netif_t *esp_netif)
         ppp_ctx->ppp->settings.lcp_echo_fails = LCP_MAXECHOFAILS;
     }
 #endif
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    if (ppp_ctx->ppp_our_ip4_addr != 0) {
+        // Set our preferred address, and accept the remote
+        ppp_ctx->ppp->ipcp_wantoptions.ouraddr = ppp_ctx->ppp_our_ip4_addr;
+        ppp_ctx->ppp->ipcp_wantoptions.accept_remote = 1;
+    }
+    if (ppp_ctx->ppp_their_ip4_addr != 0) {
+        // Set their preferred address, and accept the local
+        ppp_ctx->ppp->ipcp_wantoptions.hisaddr = ppp_ctx->ppp_their_ip4_addr;
+        ppp_ctx->ppp->ipcp_wantoptions.accept_local = 1;
+    }
+#endif // CONFIG_LWIP_PPP_SERVER_SUPPORT
 
     ESP_LOGD(TAG, "%s: Starting PPP connection: %p", __func__, ppp_ctx->ppp);
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    esp_err_t err = ppp_listen(ppp_ctx->ppp);
+#else
     err_t err = ppp_connect(ppp_ctx->ppp, 0);
+#endif
     if (err != ESP_OK) {
         ESP_LOGE(TAG, "%s: PPP connection cannot be started", __func__);
         if (ppp_ctx->ppp_error_event_enabled) {
@@ -303,6 +323,10 @@ esp_err_t esp_netif_ppp_set_params(esp_netif_t *netif, const esp_netif_ppp_confi
     obj->ppp_error_event_enabled = config->ppp_error_event_enabled;
 #ifdef CONFIG_LWIP_ENABLE_LCP_ECHO
     obj->ppp_lcp_echo_disabled = config->ppp_lcp_echo_disabled;
+#endif
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    obj->ppp_our_ip4_addr = config->ppp_our_ip4_addr;
+    obj->ppp_their_ip4_addr = config->ppp_their_ip4_addr;
 #endif
     return ESP_OK;
 }
@@ -319,5 +343,10 @@ esp_err_t esp_netif_ppp_get_params(esp_netif_t *netif, esp_netif_ppp_config_t *c
 #ifdef CONFIG_LWIP_ENABLE_LCP_ECHO
     config->ppp_lcp_echo_disabled = obj->ppp_lcp_echo_disabled;
 #endif
+#ifdef CONFIG_LWIP_PPP_SERVER_SUPPORT
+    config->ppp_our_ip4_addr = obj->ppp_our_ip4_addr;
+    config->ppp_their_ip4_addr = obj->ppp_their_ip4_addr;
+#endif
+
     return ESP_OK;
 }

components/lwip/Kconfig

@@ -941,6 +941,13 @@ menu "LWIP"
         help
             Enable Microsoft Point-to-Point Encryption (MPPE) support
 
+    config LWIP_PPP_SERVER_SUPPORT
+        bool "Enable PPP server support"
+        depends on LWIP_PPP_SUPPORT
+        default n
+        help
+            Enable to use PPP server
+
     config LWIP_ENABLE_LCP_ECHO
         bool "Enable LCP ECHO"
         depends on LWIP_PPP_SUPPORT

components/lwip/port/include/lwipopts.h

@@ -1082,6 +1082,11 @@ static inline uint32_t timeout_from_offered(uint32_t lease, uint32_t min)
  */
 #define MPPE_SUPPORT                    CONFIG_LWIP_PPP_MPPE_SUPPORT
 
+/**
+ * PPP_SERVER==1: Enable PPP server support (waiting for incoming PPP session).
+ */
+#define PPP_SERVER                      CONFIG_LWIP_PPP_SERVER_SUPPORT
+
 /**
  * PPP_MAXIDLEFLAG: Max Xmit idle time (in ms) before resend flag char.
  * TODO: If PPP_MAXIDLEFLAG > 0 and next package is send during PPP_MAXIDLEFLAG time,