net: make Server.prototype.unref() persistent

lib/net.js

@@ -1038,6 +1038,7 @@ function Server(options, connectionListener) {
   this._handle = null;
   this._usingSlaves = false;
   this._slaves = [];
+  this._unref = false;
 
   this.allowHalfOpen = options.allowHalfOpen || false;
   this.pauseOnConnect = !!options.pauseOnConnect;
@@ -1171,6 +1172,10 @@ Server.prototype._listen2 = function(address, port, addressType, backlog, fd) {
   // generate connection key, this should be unique to the connection
   this._connectionKey = addressType + ':' + address + ':' + port;
 
+  // unref the handle if the server was unref'ed prior to listening
+  if (this._unref)
+    this.unref();
+
   process.nextTick(function() {
     // ensure handle hasn't closed
     if (self._handle)
@@ -1440,11 +1445,15 @@ Server.prototype._setupSlave = function(socketList) {
 };
 
 Server.prototype.ref = function() {
+  this._unref = false;
+
   if (this._handle)
     this._handle.ref();
 };
 
 Server.prototype.unref = function() {
+  this._unref = true;
+
   if (this._handle)
     this._handle.unref();
 };

test/parallel/test-net-server-unref-persistent.js

@@ -0,0 +1,20 @@
+var common = require('../common');
+var assert = require('assert');
+var net = require('net');
+var closed = false;
+var server = net.createServer();
+
+// unref before listening
+server.unref();
+server.listen();
+
+// If the timeout fires, that means the server held the event loop open
+// and the unref() was not persistent. Close the server and fail the test.
+setTimeout(function() {
+  closed = true;
+  server.close();
+}, 1000).unref();
+
+process.on('exit', function() {
+  assert.strictEqual(closed, false, 'server should not hold loop open');
+});