dgram: check close callback is function

PR-URL: #609
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Evan Lucas <evanlucas@me.com>

lib/dgram.js

@@ -341,7 +341,7 @@ function afterSend(err) {
 
 
 Socket.prototype.close = function(callback) {
-  if (callback)
+  if (typeof callback === 'function')
     this.on('close', callback);
   this._healthCheck();
   this._stopReceiving();

test/parallel/test-dgram-close-is-not-callback.js

@@ -0,0 +1,21 @@
+var assert = require('assert');
+var common = require('../common');
+var dgram = require('dgram');
+
+var buf = new Buffer(1024);
+buf.fill(42);
+
+var socket = dgram.createSocket('udp4');
+var closeEvents = 0;
+socket.send(buf, 0, buf.length, common.PORT, 'localhost');
+
+// if close callback is not function, ignore the argument.
+socket.close('bad argument');
+
+socket.on('close', function() {
+  ++closeEvents;
+});
+
+process.on('exit', function() {
+  assert.equal(closeEvents, 1);
+});