From: Felix Fietkau <nbd@nbd.name>
Date: Wed, 11 Jun 2025 18:31:39 +0200
Subject: [PATCH] uloop: add guard() function

This allows calling the provided handler on exceptions, avoiding the
existing behavior of calling uloop_end().

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/lib/uloop.c
+++ b/lib/uloop.c
@@ -114,27 +114,48 @@ uc_uloop_cb_free(uc_uloop_cb_t *cb)
 }
 
 static bool
+uc_uloop_vm_call(uc_vm_t *vm, bool mcall, size_t nargs)
+{
+	uc_value_t *exh, *val;
+
+	if (uc_vm_call(vm, mcall, nargs) == EXCEPTION_NONE)
+		return true;
+
+	exh = uc_vm_registry_get(vm, "uloop.ex_handler");
+	if (!ucv_is_callable(exh))
+		goto error;
+
+	val = uc_vm_exception_object(vm);
+	uc_vm_stack_push(vm, ucv_get(exh));
+	uc_vm_stack_push(vm, val);
+
+	if (uc_vm_call(vm, false, 1) != EXCEPTION_NONE)
+		goto error;
+
+	ucv_put(uc_vm_stack_pop(vm));
+
+	return false;
+
+error:
+	uloop_end();
+	return false;
+}
+
+static void
 uc_uloop_cb_invoke(uc_uloop_cb_t *cb, uc_value_t *arg)
 {
 	uc_vm_t *vm = cb->vm;
 	uc_value_t *func = ucv_resource_value_get(cb->obj, 0);
 
 	if (!ucv_is_callable(func))
-		return false;
+		return;
 
 	uc_vm_stack_push(vm, ucv_get(cb->obj));
 	uc_vm_stack_push(vm, ucv_get(func));
 	uc_vm_stack_push(vm, ucv_get(arg));
 
-	if (uc_vm_call(vm, true, 1) != EXCEPTION_NONE) {
-		uloop_end();
-
-		return false;
-	}
-
-	ucv_put(uc_vm_stack_pop(vm));
-
-	return true;
+	if (uc_uloop_vm_call(vm, true, 1))
+		ucv_put(uc_vm_stack_pop(vm));
 }
 
 /**
@@ -1550,11 +1571,8 @@ uc_uloop_task_output_cb(struct uloop_fd
 					uc_vm_stack_push(vm, ucv_get(obj));
 					uc_vm_stack_push(vm, ucv_get(task->input_cb));
 
-					if (uc_vm_call(vm, true, 0) != EXCEPTION_NONE) {
-						uloop_end();
-
+					if (!uc_uloop_vm_call(vm, true, 0))
 						return;
-					}
 
 					msg = uc_vm_stack_pop(vm);
 					uc_uloop_pipe_send_common(vm, msg, task->input_fd);
@@ -1572,14 +1590,10 @@ uc_uloop_task_output_cb(struct uloop_fd
 				uc_vm_stack_push(vm, ucv_get(task->output_cb));
 				uc_vm_stack_push(vm, msg);
 
-				if (uc_vm_call(vm, true, 1) == EXCEPTION_NONE) {
-					ucv_put(uc_vm_stack_pop(vm));
-				}
-				else {
-					uloop_end();
-
+				if (!uc_uloop_vm_call(vm, true, 1))
 					return;
-				}
+
+				ucv_put(uc_vm_stack_pop(vm));
 			}
 			else {
 				ucv_put(msg);
@@ -1703,7 +1717,7 @@ uc_uloop_task(uc_vm_t *vm, size_t nargs)
 		uc_vm_stack_push(vm, func);
 		uc_vm_stack_push(vm, ucv_get(p));
 
-		if (uc_vm_call(vm, false, 1) == EXCEPTION_NONE) {
+		if (uc_uloop_vm_call(vm, false, 1)) {
 			res = uc_vm_stack_pop(vm);
 			uc_uloop_pipe_send_common(vm, res, tpipe->output);
 			ucv_put(res);
@@ -2167,6 +2181,22 @@ uc_uloop_signal(uc_vm_t *vm, size_t narg
 }
 #endif
 
+static uc_value_t *
+uc_uloop_guard(uc_vm_t *vm, size_t nargs)
+{
+	uc_value_t *arg = uc_fn_arg(0);
+
+	if (!nargs)
+		return ucv_get(uc_vm_registry_get(vm, "uloop.ex_handler"));
+
+	if (arg && !ucv_is_callable(arg))
+		return NULL;
+
+	uc_vm_registry_set(vm, "uloop.ex_handler", ucv_get(arg));
+
+	return ucv_boolean_new(true);
+}
+
 
 static const uc_function_list_t timer_fns[] = {
 	{ "set",		uc_uloop_timer_set },
@@ -2233,6 +2263,7 @@ static const uc_function_list_t global_f
 #ifdef HAVE_ULOOP_SIGNAL
 	{ "signal",		uc_uloop_signal },
 #endif
+	{ "guard",		uc_uloop_guard },
 };