Support configuring a function as 404 error handling

Signed-off-by: Jianhui Zhao <jianhuizhao329@gmail.com>

src/client.c

@@ -122,6 +122,11 @@ static void uh_handle_request(struct uh_client *cl)
     if (handle_file_request(cl, path))
 		return;
 
+    if (cl->srv->error404_cb) {
+        cl->srv->error404_cb(cl);
+        return;
+    }
+
 	cl->send_error(cl, 404, "Not Found", "The requested PATH %s was not found on this server.", path);
 }
 

src/uhttpd.h

@@ -30,10 +30,11 @@ struct uh_server {
     struct avl_tree actions;
     struct list_head clients;
 
-
 	void (*free)(struct uh_server *srv);
     void (*set_docroot)(struct uh_server *srv, const char *docroot);
     void (*set_index_file)(struct uh_server *srv, const char *index_file);
+    void (*error404_cb)(struct uh_client *cl);
+
 #if (UHTTPD_SSL_SUPPORT)
     int (*ssl_init)(struct uh_server *srv, const char *key, const char *crt);
 #endif