Add promise hooks

bnoordhuis · bnoordhuis · commit 247f0fc1928c · 2025-04-22T21:18:24.000+02:00
Lets embedders track promise chains. Closely modelled after the V8 API of the same name. Fixes: #1030
diff --git a/api-test.c b/api-test.c
@@ -18,7 +18,7 @@ static int timeout_interrupt_handler(JSRuntime *rt, void *opaque)
 
 static void sync_call(void)
 {
-    const char *code =
+    static const char code[] =
 "(function() { \
     try { \
         while (true) {} \
@@ -43,7 +43,7 @@ static void sync_call(void)
 
 static void async_call(void)
 {
-    const char *code =
+    static const char code[] =
 "(async function() { \
     const loop = async () => { \
         await Promise.resolve(); \
@@ -85,7 +85,7 @@ static JSValue save_value(JSContext *ctx, JSValueConst this_val,
 
 static void async_call_stack_overflow(void)
 {
-    const char *code =
+    static const char code[] =
 "(async function() { \
     const f = () => f(); \
     try { \
@@ -199,7 +199,7 @@ static JSModuleDef *loader(JSContext *ctx, const char *name, void *opaque)
 static void module_serde(void)
 {
     JSRuntime *rt = JS_NewRuntime();
-    JS_SetDumpFlags(rt, JS_DUMP_MODULE_RESOLVE);
+    //JS_SetDumpFlags(rt, JS_DUMP_MODULE_RESOLVE);
     JS_SetModuleLoaderFunc(rt, NULL, loader, NULL);
     JSContext *ctx = JS_NewContext(rt);
     static const char code[] = "import {f} from 'b'; f()";
@@ -311,6 +311,169 @@ function addItem() { \
     JS_FreeRuntime(rt);
 }
 
+struct {
+    int hook_type_call_count[4];
+} promise_hook_state;
+
+static void promise_hook_cb(JSContext *ctx, JSPromiseHookType type,
+                            JSValueConst promise, JSValueConst parent_promise,
+                            void *opaque)
+{
+    assert(type == JS_PROMISE_HOOK_INIT ||
+           type == JS_PROMISE_HOOK_BEFORE ||
+           type == JS_PROMISE_HOOK_AFTER ||
+           type == JS_PROMISE_HOOK_RESOLVE);
+    promise_hook_state.hook_type_call_count[type]++;
+    assert(opaque == (void *)&promise_hook_state);
+    if (!JS_IsUndefined(parent_promise)) {
+        JSValue global_object = JS_GetGlobalObject(ctx);
+        JS_SetPropertyStr(ctx, global_object, "actual",
+                          JS_DupValue(ctx, parent_promise));
+        JS_FreeValue(ctx, global_object);
+    }
+}
+
+static void promise_hook(void)
+{
+    int *cc = promise_hook_state.hook_type_call_count;
+    JSContext *unused;
+    JSRuntime *rt = JS_NewRuntime();
+    //JS_SetDumpFlags(rt, JS_DUMP_PROMISE);
+    JS_SetPromiseHook(rt, promise_hook_cb, &promise_hook_state);
+    JSContext *ctx = JS_NewContext(rt);
+    JSValue global_object = JS_GetGlobalObject(ctx);
+    {
+        // empty module; creates an outer and inner module promise;
+        // JS_Eval returns the outer promise
+        JSValue ret = JS_Eval(ctx, "", 0, "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret));
+        JS_FreeValue(ctx, ret);
+        assert(2 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(2 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(!JS_IsJobPending(rt));
+    }
+    memset(&promise_hook_state, 0, sizeof(promise_hook_state));
+    {
+        // module with unresolved promise; the outer and inner module promises
+        // are resolved but not the user's promise
+        static const char code[] = "new Promise(() => {})";
+        JSValue ret = JS_Eval(ctx, code, strlen(code), "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret)); // outer module promise
+        JS_FreeValue(ctx, ret);
+        assert(3 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(2 == cc[JS_PROMISE_HOOK_RESOLVE]); // outer and inner module promise
+        assert(!JS_IsJobPending(rt));
+    }
+    memset(&promise_hook_state, 0, sizeof(promise_hook_state));
+    {
+        // module with resolved promise
+        static const char code[] = "new Promise((resolve,reject) => resolve())";
+        JSValue ret = JS_Eval(ctx, code, strlen(code), "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret)); // outer module promise
+        JS_FreeValue(ctx, ret);
+        assert(3 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(3 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(!JS_IsJobPending(rt));
+    }
+    memset(&promise_hook_state, 0, sizeof(promise_hook_state));
+    {
+        // module with rejected promise
+        static const char code[] = "new Promise((resolve,reject) => reject())";
+        JSValue ret = JS_Eval(ctx, code, strlen(code), "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret)); // outer module promise
+        JS_FreeValue(ctx, ret);
+        assert(3 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(2 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(!JS_IsJobPending(rt));
+    }
+    memset(&promise_hook_state, 0, sizeof(promise_hook_state));
+    {
+        // module with promise chain
+        static const char code[] =
+            "globalThis.count = 0;"
+            "globalThis.actual = undefined;" // set by promise_hook_cb
+            "globalThis.expected = new Promise(resolve => resolve());"
+            "expected.then(_ => count++)";
+        JSValue ret = JS_Eval(ctx, code, strlen(code), "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret)); // outer module promise
+        JS_FreeValue(ctx, ret);
+        assert(4 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(3 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        JSValue v = JS_GetPropertyStr(ctx, global_object, "count");
+        assert(!JS_IsException(v));
+        int32_t count;
+        assert(0 == JS_ToInt32(ctx, &count, v));
+        assert(0 == count);
+        JS_FreeValue(ctx, v);
+        assert(JS_IsJobPending(rt));
+        assert(1 == JS_ExecutePendingJob(rt, &unused));
+        assert(!JS_HasException(ctx));
+        assert(4 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(4 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(!JS_IsJobPending(rt));
+        v = JS_GetPropertyStr(ctx, global_object, "count");
+        assert(!JS_IsException(v));
+        assert(0 == JS_ToInt32(ctx, &count, v));
+        assert(1 == count);
+        JS_FreeValue(ctx, v);
+        JSValue actual = JS_GetPropertyStr(ctx, global_object, "actual");
+        JSValue expected = JS_GetPropertyStr(ctx, global_object, "expected");
+        assert(!JS_IsException(actual));
+        assert(!JS_IsException(expected));
+        assert(JS_IsSameValue(ctx, actual, expected));
+        JS_FreeValue(ctx, actual);
+        JS_FreeValue(ctx, expected);
+    }
+    memset(&promise_hook_state, 0, sizeof(promise_hook_state));
+    {
+        // module with thenable; fires before and after hooks
+        static const char code[] =
+            "new Promise(resolve => resolve({then(resolve){ resolve() }}))";
+        JSValue ret = JS_Eval(ctx, code, strlen(code), "<input>", JS_EVAL_TYPE_MODULE);
+        assert(!JS_IsException(ret));
+        assert(JS_IsPromise(ret));
+        assert(JS_PROMISE_FULFILLED == JS_PromiseState(ctx, ret)); // outer module promise
+        JS_FreeValue(ctx, ret);
+        assert(3 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(0 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(0 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(2 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(JS_IsJobPending(rt));
+        assert(1 == JS_ExecutePendingJob(rt, &unused));
+        assert(!JS_HasException(ctx));
+        assert(3 == cc[JS_PROMISE_HOOK_INIT]);
+        assert(1 == cc[JS_PROMISE_HOOK_BEFORE]);
+        assert(1 == cc[JS_PROMISE_HOOK_AFTER]);
+        assert(3 == cc[JS_PROMISE_HOOK_RESOLVE]);
+        assert(!JS_IsJobPending(rt));
+    }
+    JS_FreeValue(ctx, global_object);
+    JS_FreeContext(ctx);
+    JS_FreeRuntime(rt);
+}
+
 int main(void)
 {
     sync_call();
@@ -321,5 +484,6 @@ int main(void)
     module_serde();
     two_byte_string();
     weak_map_gc_check();
+    promise_hook();
     return 0;
 }
diff --git a/quickjs.c b/quickjs.c
@@ -237,6 +237,11 @@ typedef struct JSRuntimeFinalizerState {
     void *arg;
 } JSRuntimeFinalizerState;
 
+typedef struct JSValueLink {
+    struct JSValueLink *next;
+    JSValueConst value;
+} JSValueLink;
+
 struct JSRuntime {
     JSMallocFunctions mf;
     JSMallocState malloc_state;
@@ -284,6 +289,12 @@ struct JSRuntime {
     JSInterruptHandler *interrupt_handler;
     void *interrupt_opaque;
 
+    JSPromiseHook *promise_hook;
+    void *promise_hook_opaque;
+    // for smuggling the parent promise from js_promise_then
+    // to js_promise_constructor
+    JSValueLink *parent_promise;
+
     JSHostPromiseRejectionTracker *host_promise_rejection_tracker;
     void *host_promise_rejection_tracker_opaque;
 
@@ -50199,6 +50210,12 @@ static JSValue promise_reaction_job(JSContext *ctx, int argc,
     return res2;
 }
 
+void JS_SetPromiseHook(JSRuntime *rt, JSPromiseHook promise_hook, void *opaque)
+{
+    rt->promise_hook = promise_hook;
+    rt->promise_hook_opaque = opaque;
+}
+
 void JS_SetHostPromiseRejectionTracker(JSRuntime *rt,
                                        JSHostPromiseRejectionTracker *cb,
                                        void *opaque)
@@ -50222,6 +50239,14 @@ static void fulfill_or_reject_promise(JSContext *ctx, JSValueConst promise,
 
     promise_trace(ctx, "fulfill_or_reject_promise: is_reject=%d\n", is_reject);
 
+    if (s->promise_state == JS_PROMISE_FULFILLED) {
+        JSRuntime *rt = ctx->rt;
+        if (rt->promise_hook) {
+            rt->promise_hook(ctx, JS_PROMISE_HOOK_RESOLVE, promise,
+                             JS_UNDEFINED, rt->promise_hook_opaque);
+        }
+    }
+
     if (s->promise_state == JS_PROMISE_REJECTED && !s->is_handled) {
         JSRuntime *rt = ctx->rt;
         if (rt->host_promise_rejection_tracker) {
@@ -50260,6 +50285,7 @@ static JSValue js_promise_resolve_thenable_job(JSContext *ctx,
 {
     JSValueConst promise, thenable, then;
     JSValue args[2], res;
+    JSRuntime *rt;
 
     promise_trace(ctx, "js_promise_resolve_thenable_job\n");
 
@@ -50269,7 +50295,16 @@ static JSValue js_promise_resolve_thenable_job(JSContext *ctx,
     then = argv[2];
     if (js_create_resolving_functions(ctx, args, promise) < 0)
         return JS_EXCEPTION;
+    rt = ctx->rt;
+    if (rt->promise_hook) {
+        rt->promise_hook(ctx, JS_PROMISE_HOOK_BEFORE, promise, JS_UNDEFINED,
+                         rt->promise_hook_opaque);
+    }
     res = JS_Call(ctx, then, thenable, 2, vc(args));
+    if (rt->promise_hook) {
+        rt->promise_hook(ctx, JS_PROMISE_HOOK_AFTER, promise, JS_UNDEFINED,
+                         rt->promise_hook_opaque);
+    }
     if (JS_IsException(res)) {
         JSValue error = JS_GetException(ctx);
         res = JS_Call(ctx, args[1], JS_UNDEFINED, 1, vc(&error));
@@ -50452,6 +50487,7 @@ static JSValue js_promise_constructor(JSContext *ctx, JSValueConst new_target,
     JSValueConst executor;
     JSValue obj;
     JSPromiseData *s;
+    JSRuntime *rt;
     JSValue args[2], ret;
     int i;
 
@@ -50472,6 +50508,14 @@ static JSValue js_promise_constructor(JSContext *ctx, JSValueConst new_target,
     JS_SetOpaqueInternal(obj, s);
     if (js_create_resolving_functions(ctx, args, obj))
         goto fail;
+    rt = ctx->rt;
+    if (rt->promise_hook) {
+        JSValueConst parent_promise = JS_UNDEFINED;
+        if (rt->parent_promise)
+            parent_promise = rt->parent_promise->value;
+        rt->promise_hook(ctx, JS_PROMISE_HOOK_INIT, obj, parent_promise,
+                         rt->promise_hook_opaque);
+    }
     ret = JS_Call(ctx, executor, JS_UNDEFINED, 2, vc(args));
     if (JS_IsException(ret)) {
         JSValue ret2, error;
@@ -50529,8 +50573,7 @@ static JSValue js_new_promise_capability(JSContext *ctx,
 
     executor = js_promise_executor_new(ctx);
     if (JS_IsException(executor))
-        return executor;
-
+        return JS_EXCEPTION;
     if (JS_IsUndefined(ctor)) {
         result_promise = js_promise_constructor(ctx, ctor, 1, vc(&executor));
     } else {
@@ -51005,7 +51048,10 @@ static JSValue js_promise_then(JSContext *ctx, JSValueConst this_val,
                                int argc, JSValueConst *argv)
 {
     JSValue ctor, result_promise, resolving_funcs[2];
+    bool have_promise_hook;
+    JSValueLink link;
     JSPromiseData *s;
+    JSRuntime *rt;
     int i, ret;
 
     s = JS_GetOpaque2(ctx, this_val, JS_CLASS_PROMISE);
@@ -51015,7 +51061,16 @@ static JSValue js_promise_then(JSContext *ctx, JSValueConst this_val,
     ctor = JS_SpeciesConstructor(ctx, this_val, JS_UNDEFINED);
     if (JS_IsException(ctor))
         return ctor;
+    rt = ctx->rt;
+    // always restore, even if js_new_promise_capability callee removes hook
+    have_promise_hook = (rt->promise_hook != NULL);
+    if (have_promise_hook) {
+        link = (JSValueLink){rt->parent_promise, this_val};
+        rt->parent_promise = &link;
+    }
     result_promise = js_new_promise_capability(ctx, resolving_funcs, ctor);
+    if (have_promise_hook)
+        rt->parent_promise = link.next;
     JS_FreeValue(ctx, ctor);
     if (JS_IsException(result_promise))
         return result_promise;
diff --git a/quickjs.h b/quickjs.h
@@ -1003,6 +1003,23 @@ JS_EXTERN bool JS_IsPromise(JSValueConst val);
 
 JS_EXTERN JSValue JS_NewSymbol(JSContext *ctx, const char *description, bool is_global);
 
+typedef enum JSPromiseHookType {
+    JS_PROMISE_HOOK_INIT,     // emitted when a new promise is created
+    JS_PROMISE_HOOK_BEFORE,   // runs right before promise.then is invoked
+    JS_PROMISE_HOOK_AFTER,    // runs right after promise.then is invoked
+    JS_PROMISE_HOOK_RESOLVE,  // not emitted for rejected promises
+} JSPromiseHookType;
+
+// parent_promise is only passed in when type == JS_PROMISE_HOOK_INIT and
+// is then either a promise object or JS_UNDEFINED if the new promise does
+// not have a parent promise; only promises created with promise.then have
+// a parent promise
+typedef void JSPromiseHook(JSContext *ctx, JSPromiseHookType type,
+                           JSValueConst promise, JSValueConst parent_promise,
+                           void *opaque);
+JS_EXTERN void JS_SetPromiseHook(JSRuntime *rt, JSPromiseHook promise_hook,
+                                 void *opaque);
+
 /* is_handled = true means that the rejection is handled */
 typedef void JSHostPromiseRejectionTracker(JSContext *ctx, JSValueConst promise,
                                            JSValueConst reason,
