events: fix EventTarget support

Remove support for multiple arguments (which don't actually work for EventTarget). Use our EventTarget implementation rather than a mock. Refactor `once` code in preparation of `on` using shared code for supporting `on` with `EventTarget`s.
nodejs · Jun 6, 2020 · 62e24d9 · 62e24d9
1 parent e0586d0
commit 62e24d9
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Showing 2 changed files with 41 additions and 104 deletions.
diff --git a/lib/events.js b/lib/events.js
@@ -616,41 +616,18 @@ function unwrapListeners(arr) {
 
 function once(emitter, name) {
   return new Promise((resolve, reject) => {
-    if (typeof emitter.addEventListener === 'function') {
-      // EventTarget does not have `error` event semantics like Node
-      // EventEmitters, we do not listen to `error` events here.
-      emitter.addEventListener(
-        name,
-        (...args) => { resolve(args); },
-        { once: true }
-      );
-      return;
-    }
-
-    const eventListener = (...args) => {
-      if (errorListener !== undefined) {
+    const errorListener = (err) => {
+      emitter.removeListener(name, resolver);
+      reject(err);
+    };
+    const resolver = (...args) => {
+      if (typeof emitter.removeListener === 'function') {
         emitter.removeListener('error', errorListener);
       }
       resolve(args);
     };
-    let errorListener;
-
-    // Adding an error listener is not optional because
-    // if an error is thrown on an event emitter we cannot
-    // guarantee that the actual event we are waiting will
-    // be fired. The result could be a silent way to create
-    // memory or file descriptor leaks, which is something
-    // we should avoid.
-    if (name !== 'error') {
-      errorListener = (err) => {
-        emitter.removeListener(name, eventListener);
-        reject(err);
-      };
-
-      emitter.once('error', errorListener);
-    }
-
-    emitter.once(name, eventListener);
+    eventTargetAgnosticAddListener(emitter, name, resolver, { once: true });
+    addErrorHandlerIfEventEmitter(emitter, errorListener, { once: true });
   });
 }
 
@@ -661,6 +638,28 @@ function createIterResult(value, done) {
   return { value, done };
 }
 
+function addErrorHandlerIfEventEmitter(emitter, handler, flags) {
+  if (typeof emitter.on === 'function') {
+    eventTargetAgnosticAddListener(emitter, 'error', handler, flags);
+  }
+}
+function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
+  if (typeof emitter.addEventListener === 'function') {
+    // EventTarget does not have `error` event semantics like Node
+    // EventEmitters, we do not listen to `error` events here.
+    emitter.addEventListener(name, (arg) => { listener(arg); }, flags);
+    return;
+  } else if (typeof emitter.on === 'function') {
+    if (flags.once) {
+      emitter.once(name, listener);
+    } else {
+      emitter.on(name, listener);
+    }
+  } else {
+    throw new ERR_INVALID_ARG_TYPE('emitter', 'EventEmitter', typeof emitter);
+  }
+}
+
 function on(emitter, event) {
   const unconsumedEvents = [];
   const unconsumedPromises = [];

diff --git a/test/parallel/test-events-once.js b/test/parallel/test-events-once.js
@@ -1,55 +1,10 @@
 'use strict';
+// Flags: --expose-internals
 
 const common = require('../common');
 const { once, EventEmitter } = require('events');
 const { strictEqual, deepStrictEqual } = require('assert');
-
-class EventTargetMock {
-  constructor() {
-    this.events = {};
-  }
-
-  addEventListener = common.mustCall(function(name, listener, options) {
-    if (!(name in this.events)) {
-      this.events[name] = { listeners: [], options };
-    }
-    this.events[name].listeners.push(listener);
-  });
-
-  removeEventListener = common.mustCall(function(name, callback) {
-    if (!(name in this.events)) {
-      return;
-    }
-    const event = this.events[name];
-    const stack = event.listeners;
-
-    for (let i = 0, l = stack.length; i < l; i++) {
-      if (stack[i] === callback) {
-        stack.splice(i, 1);
-        if (stack.length === 0) {
-          Reflect.deleteProperty(this.events, name);
-        }
-        return;
-      }
-    }
-  });
-
-  dispatchEvent = function(name, ...arg) {
-    if (!(name in this.events)) {
-      return true;
-    }
-    const event = this.events[name];
-    const stack = event.listeners.slice();
-
-    for (let i = 0, l = stack.length; i < l; i++) {
-      stack[i].apply(this, arg);
-      if (event.options.once) {
-        this.removeEventListener(name, stack[i]);
-      }
-    }
-    return !name.defaultPrevented;
-  };
-}
+const { EventTarget, Event } = require('internal/event_target');
 
 async function onceAnEvent() {
   const ee = new EventEmitter();
@@ -104,8 +59,6 @@ async function stopListeningAfterCatchingError() {
     ee.emit('myevent', 42, 24);
   });
 
-  process.on('multipleResolves', common.mustNotCall());
-
   try {
     await once(ee, 'myevent');
   } catch (_e) {
@@ -132,38 +85,24 @@ async function onceError() {
 }
 
 async function onceWithEventTarget() {
-  const et = new EventTargetMock();
-
+  const et = new EventTarget();
+  const event = new Event('myevent');
   process.nextTick(() => {
-    et.dispatchEvent('myevent', 42);
+    et.dispatchEvent(event);
   });
   const [ value ] = await once(et, 'myevent');
-  strictEqual(value, 42);
-  strictEqual(Reflect.has(et.events, 'myevent'), false);
-}
-
-async function onceWithEventTargetTwoArgs() {
-  const et = new EventTargetMock();
-
-  process.nextTick(() => {
-    et.dispatchEvent('myevent', 42, 24);
-  });
-
-  const value = await once(et, 'myevent');
-  deepStrictEqual(value, [42, 24]);
+  strictEqual(value, event);
 }
 
 async function onceWithEventTargetError() {
-  const et = new EventTargetMock();
-
-  const expected = new Error('kaboom');
+  const et = new EventTarget();
+  const error = new Event('error');
   process.nextTick(() => {
-    et.dispatchEvent('error', expected);
+    et.dispatchEvent(error);
   });
 
-  const [err] = await once(et, 'error');
-  strictEqual(err, expected);
-  strictEqual(Reflect.has(et.events, 'error'), false);
+  const [ err ] = await once(et, 'error');
+  strictEqual(err, error);
 }
 
 Promise.all([
@@ -173,6 +112,5 @@ Promise.all([
   stopListeningAfterCatchingError(),
   onceError(),
   onceWithEventTarget(),
-  onceWithEventTargetTwoArgs(),
   onceWithEventTargetError(),
 ]).then(common.mustCall());