From 0f485172ce3b1ab858ceb8afb272e2bef6d594c3 Mon Sep 17 00:00:00 2001
From: Erick Wendel <erick.workspace@gmail.com>
Date: Fri, 17 Dec 2021 12:04:29 -0300
Subject: [PATCH] lib: child process queue pending messages

It fixes the problem for the child process not receiving messages.

Fixes: https://github.com/nodejs/node/issues/41134
---
 lib/internal/child_process.js                 | 25 ++++++++++++++++++-
 .../test-esm-child-process-fork-main.mjs      | 20 +++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 test/es-module/test-esm-child-process-fork-main.mjs

diff --git a/lib/internal/child_process.js b/lib/internal/child_process.js
index 40592146ada6de..1ce3dc776dfbe8 100644
--- a/lib/internal/child_process.js
+++ b/lib/internal/child_process.js
@@ -10,6 +10,7 @@ const {
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   ReflectApply,
+  SafeSet,
   StringPrototypeSlice,
   Symbol,
   Uint8Array,
@@ -81,6 +82,7 @@ let HTTPParser;
 const MAX_HANDLE_RETRANSMISSIONS = 3;
 const kChannelHandle = Symbol('kChannelHandle');
 const kIsUsedAsStdio = Symbol('kIsUsedAsStdio');
+const kPendingMessages = Symbol('pendingMessages');
 
 // This object contain function to convert TCP objects to native handle objects
 // and back again.
@@ -526,6 +528,7 @@ class Control extends EventEmitter {
   constructor(channel) {
     super();
     this.#channel = channel;
+    this[kPendingMessages] = new SafeSet();
   }
 
   // The methods keeping track of the counter are being used to track the
@@ -699,6 +702,19 @@ function setupChannel(target, channel, serializationMode) {
     });
   });
 
+  target.on('newListener', function() {
+    if (!target.channel) return;
+
+    const messages = target.channel[kPendingMessages];
+    if (!messages.size) return;
+
+    for (const messageParams of messages) {
+      process.nextTick(() => ReflectApply(target.emit, target, messageParams));
+    }
+
+    messages.clear();
+  });
+
   target.send = function(message, handle, options, callback) {
     if (typeof handle === 'function') {
       callback = handle;
@@ -912,7 +928,14 @@ function setupChannel(target, channel, serializationMode) {
   };
 
   function emit(event, message, handle) {
-    target.emit(event, message, handle);
+    const isInternalMessage = 'internalMessage' === event;
+    const hasListenersInstalled = target.listenerCount('message');
+    if (hasListenersInstalled || isInternalMessage) {
+      target.emit(event, message, handle);
+      return;
+    }
+
+    target.channel[kPendingMessages].add([event, message, handle]);
   }
 
   function handleMessage(message, handle, internal) {
diff --git a/test/es-module/test-esm-child-process-fork-main.mjs b/test/es-module/test-esm-child-process-fork-main.mjs
new file mode 100644
index 00000000000000..c7961086494186
--- /dev/null
+++ b/test/es-module/test-esm-child-process-fork-main.mjs
@@ -0,0 +1,20 @@
+import '../common/index.mjs';
+import assert from 'assert';
+import { fork } from 'child_process';
+import { once } from 'events';
+
+if (process.argv[2] !== 'child') {
+  const currentFile = 'test-esm-child-process-fork-main.mjs';
+  const { pathname: filename } = new URL(currentFile, import.meta.url);
+  const cp = fork(filename, ['child']);
+  const message = 'Hello World';
+  cp.send(message);
+
+  const [received] = await once(cp, 'message');
+
+  assert.deepStrictEqual(received, message);
+
+  cp.disconnect();
+} else {
+  process.on('message', (msg) => process.send(msg));
+}