net: cleanup connect logic

Separates out the lookup logic for net.Socket. In the event
the `host` property is an IP address, the lookup is skipped.

PR-URL: https://github.com/iojs/io.js/pull/1505
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>

lib/net.js

@@ -881,15 +881,18 @@ Socket.prototype.connect = function(options, cb) {
     connect(self, options.path);
 
   } else {
+    lookupAndConnect(self, options);
+  }
+  return self;
+};
+
+
+function lookupAndConnect(self, options) {
   const dns = require('dns');
   var host = options.host || 'localhost';
-    var port = 0;
+  var port = options.port;
   var localAddress = options.localAddress;
   var localPort = options.localPort;
-    var dnsopts = {
-      family: options.family,
-      hints: 0
-    };
 
   if (localAddress && !exports.isIP(localAddress))
     throw new TypeError('localAddress must be a valid IP: ' + localAddress);
@@ -897,7 +900,6 @@ Socket.prototype.connect = function(options, cb) {
   if (localPort && typeof localPort !== 'number')
     throw new TypeError('localPort should be a number: ' + localPort);
 
-    port = options.port;
   if (typeof port !== 'undefined') {
     if (typeof port !== 'number' && typeof port !== 'string')
       throw new TypeError('port should be a number or string: ' + port);
@@ -906,6 +908,19 @@ Socket.prototype.connect = function(options, cb) {
   }
   port |= 0;
 
+  // If host is an IP, skip performing a lookup
+  // TODO(evanlucas) should we hot path this for localhost?
+  var addressType = exports.isIP(host);
+  if (addressType) {
+    connect(self, host, port, addressType, localAddress, localPort);
+    return;
+  }
+
+  var dnsopts = {
+    family: options.family,
+    hints: 0
+  };
+
   if (dnsopts.family !== 4 && dnsopts.family !== 6)
     dnsopts.hints = dns.ADDRCONFIG | dns.V4MAPPED;
 
@@ -936,9 +951,7 @@ Socket.prototype.connect = function(options, cb) {
               localPort);
     }
   });
-  }
+}
-  return self;
-};
 
 
 function connectErrorNT(self, err, options) {

test/parallel/test-net-dns-lookup-skip.js

@@ -0,0 +1,18 @@
+var common = require('../common');
+var assert = require('assert');
+var net = require('net');
+
+function check(addressType) {
+  var server = net.createServer(function(client) {
+    client.end();
+    server.close();
+  });
+
+  var address = addressType === 4 ? '127.0.0.1' : '::1';
+  server.listen(common.PORT, address, function() {
+    net.connect(common.PORT, address).on('lookup', assert.fail);
+  });
+}
+
+check(4);
+common.hasIPv6 && check(6);

test/parallel/test-net-dns-lookup.js

@@ -9,7 +9,7 @@ var server = net.createServer(function(client) {
 });
 
 server.listen(common.PORT, '127.0.0.1', function() {
-  net.connect(common.PORT, '127.0.0.1').on('lookup', function(err, ip, type) {
+  net.connect(common.PORT, 'localhost').on('lookup', function(err, ip, type) {
     assert.equal(err, null);
     assert.equal(ip, '127.0.0.1');
     assert.equal(type, '4');