test: fix flaky test-cluster-net-listen-ipv6only-none

test-cluster-net-listen-ipv6only-none was using port `0` for an
IPv6-only operation and assuming that the operating system would supply
a port that was also available in IPv4. However, CI results seem to
indicate that a port can be supplied that is in use by IPv4 but
available to IPv6, resulting in the test failing. Use `common.PORT` to
avoid this issue.

Fixes: https://github.com/nodejs/node/issues/29679

PR-URL: https://github.com/nodejs/node/pull/29681
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/test/sequential/test-cluster-net-listen-ipv6only-none.js b/test/sequential/test-cluster-net-listen-ipv6only-none.js
new file mode 100644
index 0000000000..d520b7f25c
--- /dev/null
+++ b/test/sequential/test-cluster-net-listen-ipv6only-none.js
@@ -0,0 +1,57 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasIPv6)
+  common.skip('no IPv6 support');
+
+const assert = require('assert');
+const cluster = require('cluster');
+const net = require('net');
+const Countdown = require('../common/countdown');
+
+// This test ensures that the `ipv6Only` option in `net.Server.listen()`
+// works as expected when we use cluster with `SCHED_NONE` schedulingPolicy.
+cluster.schedulingPolicy = cluster.SCHED_NONE;
+const host = '::';
+const WORKER_ACCOUNT = 3;
+
+if (cluster.isMaster) {
+  const workers = new Map();
+
+  const countdown = new Countdown(WORKER_ACCOUNT, () => {
+    // Make sure the `ipv6Only` option works. This is the part of the test that
+    // requires the whole test to use `common.PORT` rather than port `0`. If it
+    // used port `0` instead, then the operating system can supply a port that
+    // is available for the IPv6 interface but in use by the IPv4 interface.
+    // Refs: https://github.com/nodejs/node/issues/29679
+    const server = net.createServer().listen({
+      host: '0.0.0.0',
+      port: common.PORT,
+    }, common.mustCall(() => {
+      // Exit.
+      server.close();
+      workers.forEach((worker) => {
+        worker.disconnect();
+      });
+    }));
+  });
+
+  for (let i = 0; i < WORKER_ACCOUNT; i += 1) {
+    const worker = cluster.fork().on('exit', common.mustCall((statusCode) => {
+      assert.strictEqual(statusCode, 0);
+    })).on('listening', common.mustCall((workerAddress) => {
+      assert.strictEqual(workerAddress.addressType, 6);
+      assert.strictEqual(workerAddress.address, host);
+      assert.strictEqual(workerAddress.port, common.PORT);
+      countdown.dec();
+    }));
+
+    workers.set(i, worker);
+  }
+} else {
+  net.createServer().listen({
+    host,
+    port: common.PORT,
+    ipv6Only: true,
+  }, common.mustCall());
+}