lwip: add a hook for ip6 source address selection

components/lwip/Kconfig

@@ -1024,6 +1024,26 @@ menu "LWIP"
 
         endchoice
 
+        choice LWIP_HOOK_IP6_SELECT_SRC_ADDR
+            prompt "IPv6 source address selection Hook"
+            depends on LWIP_IPV6
+            default LWIP_HOOK_IP6_SELECT_SRC_ADDR_NONE
+            help
+                Enables custom IPv6 source address selection.
+                Setting this to "default" provides weak implementation
+                stub that could be overwritten in application code.
+                Setting this to "custom" provides hook's declaration
+                only and expects the application to implement it.
+
+            config LWIP_HOOK_IP6_SELECT_SRC_ADDR_NONE
+                bool "No hook declared"
+            config LWIP_HOOK_IP6_SELECT_SRC_ADDR_DEFAULT
+                bool "Default (weak) implementation"
+            config LWIP_HOOK_IP6_SELECT_SRC_ADDR_CUSTOM
+                bool "Custom implementation"
+
+        endchoice
+
         choice LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE
             prompt "Netconn external resolve Hook"
             default LWIP_HOOK_NETCONN_EXT_RESOLVE_DEFAULT if OPENTHREAD_DNS64_CLIENT

components/lwip/port/hooks/lwip_default_hooks.c

@@ -41,7 +41,17 @@ const ip6_addr_t *__weak lwip_hook_nd6_get_gw(struct netif *netif, const ip6_add
     LWIP_UNUSED_ARG(netif);
     LWIP_UNUSED_ARG(dest);
 
-    return 0;
+    return NULL;
+}
+#endif
+
+#ifdef CONFIG_LWIP_HOOK_IP6_SELECT_SRC_ADDR_DEFAULT
+const ip_addr_t *__weak lwip_hook_ip6_select_source_address(struct netif *netif, const ip6_addr_t *dest)
+{
+    LWIP_UNUSED_ARG(netif);
+    LWIP_UNUSED_ARG(dest);
+
+    return NULL;
 }
 #endif
 

components/lwip/port/include/lwip_default_hooks.h

@@ -43,6 +43,12 @@ const ip6_addr_t *lwip_hook_nd6_get_gw(struct netif *netif, const ip6_addr_t *de
 #define LWIP_HOOK_ND6_GET_GW lwip_hook_nd6_get_gw
 #endif /* CONFIG_LWIP_HOOK_ND6_GET_GATEWAY... */
 
+#if defined(CONFIG_LWIP_HOOK_IP6_SELECT_SRC_ADDR_CUSTOM) || defined(CONFIG_LWIP_HOOK_IP6_SELECT_SRC_ADDR_DEFAULT)
+const ip_addr_t *lwip_hook_ip6_select_source_address(struct netif *netif, const ip6_addr_t *dest);
+
+#define LWIP_HOOK_IP6_SELECT_SRC_ADDR lwip_hook_ip6_select_source_address
+#endif /* CONFIG_LWIP_HOOK_IP6_SELECT_SRC_ADDR... */
+
 #if defined(CONFIG_LWIP_HOOK_NETCONN_EXT_RESOLVE_CUSTOM) || defined(CONFIG_LWIP_HOOK_NETCONN_EXT_RESOLVE_DEFAULT)
 int lwip_hook_netconn_external_resolve(const char *name, ip_addr_t *addr, u8_t addrtype, err_t *err);