From ed8f6a3c0e25f42aacf8e4d5f3090b477675495b Mon Sep 17 00:00:00 2001
From: islandryu <shimaryuhei@gmail.com>
Date: Wed, 5 Aug 2026 00:41:17 +0900
Subject: [PATCH 1/2] cluster: report EADDRINUSE when a worker listens twice on
 the same port

Fixes: https://github.com/nodejs/node/issues/64869
Signed-off-by: islandryu <shimaryuhei@gmail.com>
---
 lib/internal/cluster/primary.js               | 12 +++++++-
 .../test-cluster-listen-twice-same-port.js    | 29 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 test/sequential/test-cluster-listen-twice-same-port.js

diff --git a/lib/internal/cluster/primary.js b/lib/internal/cluster/primary.js
index 6ab845c6d122..169f3ea60825 100644
--- a/lib/internal/cluster/primary.js
+++ b/lib/internal/cluster/primary.js
@@ -16,6 +16,7 @@ const {
 } = require('internal/errors');
 
 const assert = require('internal/assert');
+const { UV_EADDRINUSE } = internalBinding('uv');
 const { fork } = require('child_process');
 const path = require('path');
 const EventEmitter = require('events');
@@ -274,7 +275,16 @@ function queryServer(worker, message) {
               `${message.fd}` + (message.port === 0 ? `:${message.index}` : '');
   const cachedHandle = handles.get(key);
   let handle;
-  if (cachedHandle && !cachedHandle.has(worker)) {
+  if (cachedHandle) {
+    if (cachedHandle.has(worker)) {
+      send(worker, {
+        errno: UV_EADDRINUSE,
+        key,
+        ack: message.seq,
+        data: cachedHandle.data,
+      });
+      return;
+    }
     handle = cachedHandle;
   }
 
diff --git a/test/sequential/test-cluster-listen-twice-same-port.js b/test/sequential/test-cluster-listen-twice-same-port.js
new file mode 100644
index 000000000000..d522fe363f21
--- /dev/null
+++ b/test/sequential/test-cluster-listen-twice-same-port.js
@@ -0,0 +1,29 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const cluster = require('cluster');
+const net = require('net');
+
+if (cluster.isPrimary) {
+  cluster.fork().on('exit', common.mustCall((code) => {
+    assert.strictEqual(code, 0);
+  }));
+  return;
+}
+
+function listen() {
+  return new Promise((resolve, reject) => {
+    const server = net.createServer();
+    server.once('error', reject);
+    server.once('listening', () => resolve(server));
+    server.listen({ host: '127.0.0.1', port: common.PORT });
+  });
+}
+
+(async () => {
+  const server1 = await listen();
+  await assert.rejects(listen(), { code: 'EADDRINUSE' });
+  await new Promise((resolve) => server1.close(resolve));
+  cluster.worker.disconnect();
+})().then(common.mustCall());

From d095f6e42fc5941753090f2a92ce5657cc1f8d56 Mon Sep 17 00:00:00 2001
From: islandryu <shimaryuhei@gmail.com>
Date: Sun, 23 Aug 2026 16:39:55 +0900
Subject: [PATCH 2/2] test: cover SCHED_NONE and SCHED_RR in cluster
 listen-twice-same-port test

---
 .../test-cluster-listen-twice-same-port.js    | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/test/sequential/test-cluster-listen-twice-same-port.js b/test/sequential/test-cluster-listen-twice-same-port.js
index d522fe363f21..0d744dcc1278 100644
--- a/test/sequential/test-cluster-listen-twice-same-port.js
+++ b/test/sequential/test-cluster-listen-twice-same-port.js
@@ -5,6 +5,29 @@ const assert = require('assert');
 const cluster = require('cluster');
 const net = require('net');
 
+if (process.argv[2] === undefined) {
+  const { fork } = require('child_process');
+
+  function run(policy) {
+    return new Promise((resolve) => {
+      const child = fork(__filename, [policy]);
+      child.on('exit', common.mustCall((code) => {
+        assert.strictEqual(code, 0);
+        resolve();
+      }));
+    });
+  }
+
+  (async () => {
+    await run('none');
+    await run('rr');
+  })().then(common.mustCall());
+  return;
+}
+
+cluster.schedulingPolicy =
+  process.argv[2] === 'rr' ? cluster.SCHED_RR : cluster.SCHED_NONE;
+
 if (cluster.isPrimary) {
   cluster.fork().on('exit', common.mustCall((code) => {
     assert.strictEqual(code, 0);