worker: populate BroadcastChannel MessageEvent source

lib/internal/worker/io.js

@@ -48,6 +48,7 @@ const {
 } = internalBinding('messaging');
 const {
   getEnvMessagePort,
+  threadId,
 } = internalBinding('worker');
 
 const { Readable, Writable } = require('stream');
@@ -346,7 +347,7 @@ function receiveMessageOnPort(port) {
 }
 
 function onMessageEvent(type, data) {
-  this.dispatchEvent(lazyMessageEvent(type, { data }));
+  this.dispatchEvent(lazyMessageEvent(type, { data: data.value, source: data.source }));
 }
 
 function isBroadcastChannel(value) {
@@ -419,13 +420,17 @@ class BroadcastChannel extends EventTarget {
    * @returns {void}
    */
   postMessage(message) {
+    const broadcastMessage = {
+      source: threadId,
+      value: message,
+    };
     if (!isBroadcastChannel(this))
       throw new ERR_INVALID_THIS('BroadcastChannel');
     if (arguments.length === 0)
       throw new ERR_MISSING_ARGS('message');
     if (this[kHandle] === undefined)
       throw new DOMException('BroadcastChannel is closed.', 'InvalidStateError');
-    if (this[kHandle].postMessage(message) === undefined)
+    if (this[kHandle].postMessage(broadcastMessage) === undefined)
       throw new DOMException('Message could not be posted.');
   }
 

test/parallel/test-worker-broadcastchannel.js

@@ -147,7 +147,7 @@ assert.throws(() => new BroadcastChannel(), {
   const bc1 = new BroadcastChannel('channel4');
   const bc2 = new BroadcastChannel('channel4');
   bc1.postMessage('some data');
-  assert.strictEqual(receiveMessageOnPort(bc2).message, 'some data');
+  assert.strictEqual(receiveMessageOnPort(bc2).message.value, 'some data');
   assert.strictEqual(receiveMessageOnPort(bc2), undefined);
   bc1.close();
   bc2.close();
@@ -183,3 +183,32 @@ assert.throws(() => new BroadcastChannel(), {
     "BroadcastChannel { name: 'channel5', active: false }"
   );
 }
+
+{
+  const bc = new BroadcastChannel('worker-source');
+
+  new Worker(`
+    const assert = require('assert');
+    const { BroadcastChannel, threadId } = require('worker_threads');
+
+    const bc = new BroadcastChannel('worker-source');
+
+    bc.onmessage = (evt) => {
+      assert.strictEqual(evt.data, 'from-main');
+      assert.strictEqual(evt.source, 0);
+
+      bc.close();
+    };
+
+    bc.postMessage('from-worker');
+  `, { eval: true });
+
+  bc.onmessage = common.mustCall((evt) => {
+    assert.strictEqual(evt.data, 'from-worker');
+
+    assert.ok(evt.source > 0);
+
+    bc.postMessage('from-main');
+    bc.close();
+  });
+}