net: support DNS hints in createConnection()

This commit adds support for passing DNS lookup hints to
createConnection().

PR-URL: #6000
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/net.markdown

@@ -375,6 +375,8 @@ For TCP sockets, `options` argument should be an object which specifies:
 
   - `family` : Version of IP stack. Defaults to `4`.
 
+  - `hints`: [`dns.lookup()` hints][]. Defaults to `0`.
+
   - `lookup` : Custom lookup function. Defaults to `dns.lookup`.
 
 For local domain sockets, `options` argument should be an object which
@@ -720,6 +722,7 @@ Returns true if input is a version 6 IP address, otherwise returns false.
 [`connect()`]: #net_socket_connect_options_connectlistener
 [`destroy()`]: #net_socket_destroy
 [`dns.lookup()`]: dns.html#dns_dns_lookup_hostname_options_callback
+[`dns.lookup()` hints]: #dns_supported_getaddrinfo_flags
 [`end()`]: #net_socket_end_data_encoding
 [`EventEmitter`]: events.html#events_class_events_eventemitter
 [`net.Socket`]: #net_class_net_socket

lib/net.js

@@ -946,10 +946,10 @@ function lookupAndConnect(self, options) {
 
   var dnsopts = {
     family: options.family,
-    hints: 0
+    hints: options.hints || 0
   };
 
-  if (dnsopts.family !== 4 && dnsopts.family !== 6) {
+  if (dnsopts.family !== 4 && dnsopts.family !== 6 && dnsopts.hints === 0) {
     dnsopts.hints = dns.ADDRCONFIG;
     // The AI_V4MAPPED hint is not supported on FreeBSD or Android,
     // and getaddrinfo returns EAI_BADFLAGS. However, it seems to be

test/parallel/test-net-create-connection.js

@@ -1,14 +1,15 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var net = require('net');
+const common = require('../common');
+const assert = require('assert');
+const dns = require('dns');
+const net = require('net');
 
-var tcpPort = common.PORT;
-var expectedConnections = 7;
+const tcpPort = common.PORT;
+const expectedConnections = 7;
 var clientConnected = 0;
 var serverConnected = 0;
 
-var server = net.createServer(function(socket) {
+const server = net.createServer(function(socket) {
   socket.end();
   if (++serverConnected === expectedConnections) {
     server.close();
@@ -87,6 +88,10 @@ server.listen(tcpPort, 'localhost', function() {
   fail({
     port: 65536
   }, RangeError, '"port" option should be >= 0 and < 65536: 65536');
+
+  fail({
+    hints: (dns.ADDRCONFIG | dns.V4MAPPED) + 42,
+  }, TypeError, 'Invalid argument: hints must use valid flags');
 });
 
 // Try connecting to random ports, but do so once the server is closed