util: expose promise events

Author: devsnek

doc/api/util.md

@@ -1631,6 +1631,80 @@ const module = new WebAssembly.Module(wasmBuffer);
 util.types.isWebAssemblyCompiledModule(module);  // Returns true
 ```
 
+### util.createPromiseHook(hooks)
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* `hooks` {Object}
+  * `resolve` {Function} Called when a promise resolve function is called. The
+    promise is not fulfilled or rejected at this point.
+  * `rejectWithNoHandler` {Function} Called when a promise rejects without any
+    handler.
+  * `handlerAddedAfterReject` {Function} Called when a promise handler is added
+    to a promise that rejected without a handler.
+  * `rejectAfterResolved` {Function} Called when a promise reject function is
+    called after resolution.
+  * `resolveAfterResolved` {Function} Called when a promise resolve function is
+    called after resolution.
+
+Returns: {Object}
+  * `enable` {Function} Enables the hook
+  * `disable` {Function} Disables the hook
+
+Registers the promise hook `hook` to be called for certain promise debugging
+events.
+
+```js
+util.createPromiseHook({
+  resolve(promise) {
+    console.log('Promise did resolve');
+  },
+  rejectWithNoHandler(promise, value) {
+    console.log('Promise did rejectWithNoHandler with', value);
+  },
+  handlerAddedAfterReject(promise) {
+    console.log('Promise did handlerAddedAfterReject');
+  },
+}).enable();
+
+const x = Promise.resolve('success')
+  .then(() => Promise.reject('error'));
+
+setTimeout(() => {
+  x.catch(() => {});
+}, 10);
+
+// Promise did resolve
+// Promise did resolve
+// Promise did rejectWithNoHandler with 'error'
+// Promise did resolve
+// Promise did handlerAddedAfterReject
+// Promise did resolve
+// Promise did rejectWithNoHandler with 'error'
+// Promise did resolve
+// Promise did handlerAddedAfterReject
+// Promise did resolve
+```
+
+```js
+util.createPromiseHook({
+  rejectAfterResolved(promise, value) {
+    console.log('Promise did rejectAfterResolved with', value);
+  },
+}).enable();
+
+new Promise((resolve, reject) => {
+  resolve('success');
+
+  reject('oops');
+});
+
+// Promise did rejectAfterResolved with 'oops'
+```
+
 ## Deprecated APIs
 
 The following APIs are deprecated and should no longer be used. Existing

lib/util.js

@@ -21,6 +21,7 @@
 
 'use strict';
 
+const { internalBinding } = require('internal/bootstrap/loaders');
 const errors = require('internal/errors');
 const {
   ERR_FALSY_VALUE_REJECTION,
@@ -37,8 +38,8 @@ const {
   kRejected,
   previewEntries
 } = process.binding('util');
+const { setPromiseHook } = internalBinding('safe_util');
 
-const { internalBinding } = require('internal/bootstrap/loaders');
 const types = internalBinding('types');
 Object.assign(types, require('internal/util/types'));
 const {
@@ -1464,6 +1465,72 @@ function getSystemErrorName(err) {
   return internalErrorName(err);
 }
 
+const promiseEventTypes = [
+  'init',
+  'resolve',
+  'before',
+  'after',
+  'rejectWithNoHandler',
+  'handlerAddedAfterReject',
+  'rejectAfterResolved',
+  'resolveAfterResolved',
+];
+const promiseHooks = new Set();
+let promiseHookWarned = false;
+let resolveHookRef = 0;
+function promiseHookCallback(type, promise, value) {
+  type = promiseEventTypes[type];
+  for (const hooks of promiseHooks) {
+    try {
+      const hook = hooks[type];
+      if (typeof hook === 'function') {
+        hook(promise, value);
+      }
+    } catch (e) {
+      process.nextTick(() => { throw e; });
+    }
+  }
+}
+function createPromiseHook(hooks) {
+  if (!promiseHookWarned) {
+    promiseHookWarned = true;
+    process.emitWarning('The util.createPromiseHook API is experimental.',
+                        'ExperimentalWarning');
+  }
+
+  const hasResolve = 'resolve' in hooks;
+
+  promiseEventTypes.forEach((type) => {
+    const hook = hooks[type];
+    if (hook === undefined) {
+      return;
+    }
+
+    if (typeof hook !== 'function') {
+      throw new ERR_INVALID_ARG_TYPE(`hooks.${type}`, 'function', hook);
+    }
+  });
+
+  return {
+    enable() {
+      promiseHooks.add(hooks);
+      if (hasResolve) {
+        resolveHookRef++;
+      }
+      setPromiseHook(promiseHookCallback, resolveHookRef > 0);
+    },
+    disable() {
+      promiseHooks.delete(hooks);
+      if (hasResolve) {
+        resolveHookRef--;
+      }
+      setPromiseHook(
+        hooks.size === 0 ? null : promiseHookCallback,
+        resolveHookRef > 0);
+    },
+  };
+}
+
 // Keep the `exports =` so that various functions can still be monkeypatched
 module.exports = exports = {
   _errnoException: errors.errnoException,
@@ -1505,6 +1572,8 @@ module.exports = exports = {
   TextEncoder,
   types,
 
+  createPromiseHook,
+
   // Deprecated Old Stuff
   debug: deprecate(debug,
                    'util.debug is deprecated. Use console.error instead.',

src/bootstrapper.cc

@@ -16,8 +16,6 @@ using v8::Local;
 using v8::MaybeLocal;
 using v8::Object;
 using v8::Promise;
-using v8::PromiseRejectEvent;
-using v8::PromiseRejectMessage;
 using v8::String;
 using v8::Value;
 
@@ -52,30 +50,21 @@ void SetupNextTick(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(ret);
 }
 
-void PromiseRejectCallback(PromiseRejectMessage message) {
+void PromiseRejectCallback(PromiseHookType type,
+                           Local<Promise> promise,
+                           Local<Value> value,
+                           void* arg) {
   static std::atomic<uint64_t> unhandledRejections{0};
   static std::atomic<uint64_t> rejectionsHandledAfter{0};
 
-  Local<Promise> promise = message.GetPromise();
-  Isolate* isolate = promise->GetIsolate();
-  PromiseRejectEvent event = message.GetEvent();
-
-  Environment* env = Environment::GetCurrent(isolate);
+  Environment* env = static_cast<Environment*>(arg);
   Local<Function> callback;
-  Local<Value> value;
 
-  if (event == v8::kPromiseRejectWithNoHandler) {
+  if (type == PromiseHookType::kRejectWithNoHandler) {
     callback = env->promise_reject_unhandled_function();
-    value = message.GetValue();
-
-    if (value.IsEmpty())
-      value = Undefined(isolate);
-
     unhandledRejections++;
-  } else if (event == v8::kPromiseHandlerAddedAfterReject) {
+  } else if (type == PromiseHookType::kHandlerAddedAfterReject) {
     callback = env->promise_reject_handled_function();
-    value = Undefined(isolate);
-
     rejectionsHandledAfter++;
   } else {
     return;
@@ -86,10 +75,13 @@ void PromiseRejectCallback(PromiseRejectMessage message) {
                  "unhandled", unhandledRejections,
                  "handledAfter", rejectionsHandledAfter);
 
+  if (value.IsEmpty()) {
+    value = Undefined(env->isolate());
+  }
 
   Local<Value> args[] = { promise, value };
   MaybeLocal<Value> ret = callback->Call(env->context(),
-                                         Undefined(isolate),
+                                         Undefined(env->isolate()),
                                          arraysize(args),
                                          args);
 
@@ -99,14 +91,14 @@ void PromiseRejectCallback(PromiseRejectMessage message) {
 
 void SetupPromises(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
-  Isolate* isolate = env->isolate();
 
   CHECK(args[0]->IsFunction());
   CHECK(args[1]->IsFunction());
 
-  isolate->SetPromiseRejectCallback(PromiseRejectCallback);
   env->set_promise_reject_unhandled_function(args[0].As<Function>());
   env->set_promise_reject_handled_function(args[1].As<Function>());
+
+  env->AddPromiseRejectHook(PromiseRejectCallback, env);
 }
 
 #define BOOTSTRAP_METHOD(name, fn) env->SetMethod(bootstrapper, #name, fn)