net: don't emit 'close' event twice

Don't allow `socket.destroy()` to run twice. The self-destruct sequence itself
is idempotent but it makes the 'close' and 'error' events fire more than once,
which may confuse listeners.

Fixes #2223.

lib/net.js

@@ -273,6 +273,8 @@ Socket.prototype._connectQueueCleanUp = function(exception) {
 
 
 Socket.prototype.destroy = function(exception) {
+  if (this.destroyed) return;
+
   var self = this;
 
   self._connectQueueCleanUp();
@@ -283,7 +285,7 @@ Socket.prototype.destroy = function(exception) {
 
   timers.unenroll(this);
 
-  if (this.server && !this.destroyed) {
+  if (this.server) {
     this.server.connections--;
     this.server._emitCloseIfDrained();
   }

test/simple/test-net-socket-destroy-twice.js

@@ -0,0 +1,43 @@
+// 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 net = require('net');
+
+var nerrors = 0;
+var ncloses = 0;
+
+process.on('exit', function() {
+  assert.equal(nerrors, 1);
+  assert.equal(ncloses, 1);
+});
+
+var conn = net.createConnection(common.PORT);
+
+conn.on('error', function() {
+  nerrors++;
+  conn.destroy();
+});
+
+conn.on('close', function() {
+  ncloses++;
+});