cluster: fix libuv assert in net.listen()

Problem: calling `server.listen()` (no port) on a net.Server triggered the
following libuv assertion:

  node: ../deps/uv/src/unix/stream.c:406: uv__write: Assertion `fd_to_send >= 0'
  failed.

Cause: uv_tcp_t handles are lazily initialized. Omitting the port made the
handle get initialized even more lazily. Too lazily - it wasn't initialized
when the handle was sent over to the child process.

Solution: implicitly bind to a random port in listen() when the port number
is omitted, it forces the handle to initialize. This is not a change in
behavior, listen() has always been identical to listen(0).

Fixes #3325.

lib/net.js

@@ -967,9 +967,8 @@ Server.prototype.listen = function() {
   var TCP = process.binding('tcp_wrap').TCP;
 
   if (arguments.length == 0 || typeof arguments[0] == 'function') {
-    // Don't bind(). OS will assign a port with INADDR_ANY.
-    // The port can be found with server.address()
-    listen(self, null, null, backlog);
+    // Bind to a random port.
+    listen(self, '0.0.0.0', 0, null, backlog);
 
   } else if (arguments[0] && typeof arguments[0] === 'object') {
     var h = arguments[0];

test/simple/test-cluster-net-listen.js

@@ -0,0 +1,41 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var cluster = require('cluster');
+var net = require('net');
+
+if (cluster.isMaster) {
+  // ensure that the worker exits peacefully
+  var worker = cluster.fork();
+  worker.on('exit', function(statusCode) {
+    assert.equal(statusCode, 0);
+    worker = null;
+  });
+  process.on('exit', function() {
+    assert.equal(worker, null);
+  });
+}
+else {
+  // listen() without port should not trigger a libuv assert
+  net.createServer(assert.fail).listen(process.exit);
+}