cluster: send connection to other server when worker drop it

PR-URL: nodejs/node#43747
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>

Author: theanarkh

lib/internal/cluster/child.js

@@ -208,7 +208,14 @@ function rr(message, { indexesKey, index }, cb) {
 function onconnection(message, handle) {
   const key = message.key;
   const server = handles.get(key);
-  const accepted = server !== undefined;
+  let accepted = server !== undefined;
+
+  if (accepted && server[owner_symbol]) {
+    const self = server[owner_symbol];
+    if (self.maxConnections && self._connections >= self.maxConnections) {
+      accepted = false;
+    }
+  }
 
   send({ ack: message.seq, accepted });
 

test/parallel/test-cluster-net-server-drop-connection.js

@@ -0,0 +1,64 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+const cluster = require('cluster');
+const tmpdir = require('../common/tmpdir');
+
+// The core has bug in handling pipe handle by ipc when platform is win32,
+// it can be triggered on win32. I will fix it in another pr.
+if (common.isWindows)
+  common.skip('no setSimultaneousAccepts on pipe handle');
+
+let connectionCount = 0;
+let listenCount = 0;
+let worker1;
+let worker2;
+
+function request(path) {
+  for (let i = 0; i < 10; i++) {
+    net.connect(path);
+  }
+}
+
+function handleMessage(message) {
+  assert.match(message.action, /listen|connection/);
+  if (message.action === 'listen') {
+    if (++listenCount === 2) {
+      request(common.PIPE);
+    }
+  } else if (message.action === 'connection') {
+    if (++connectionCount === 10) {
+      worker1.send({ action: 'disconnect' });
+      worker2.send({ action: 'disconnect' });
+    }
+  }
+}
+
+if (cluster.isPrimary) {
+  cluster.schedulingPolicy = cluster.SCHED_RR;
+  tmpdir.refresh();
+  worker1 = cluster.fork({ maxConnections: 1, pipePath: common.PIPE });
+  worker2 = cluster.fork({ maxConnections: 9, pipePath: common.PIPE });
+  worker1.on('message', common.mustCall((message) => {
+    handleMessage(message);
+  }, 2));
+  worker2.on('message', common.mustCall((message) => {
+    handleMessage(message);
+  }, 10));
+} else {
+  const server = net.createServer(common.mustCall((socket) => {
+    process.send({ action: 'connection' });
+  }, +process.env.maxConnections));
+
+  server.listen(process.env.pipePath, common.mustCall(() => {
+    process.send({ action: 'listen' });
+  }));
+
+  server.maxConnections = +process.env.maxConnections;
+
+  process.on('message', common.mustCall((message) => {
+    assert.strictEqual(message.action, 'disconnect');
+    process.disconnect();
+  }));
+}