dns: minor refactor of dns module

Move to the more efficient module.exports = {} pattern.

PR-URL: https://github.com/nodejs/node/pull/11597
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Claudio Rodriguez <cjrodr@yahoo.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/dns.js

@@ -99,7 +99,7 @@ function onlookupall(err, addresses) {
 
 // Easy DNS A/AAAA look up
 // lookup(hostname, [options,] callback)
-exports.lookup = function lookup(hostname, options, callback) {
+function lookup(hostname, options, callback) {
   var hints = 0;
   var family = -1;
   var all = false;
@@ -119,9 +119,9 @@ exports.lookup = function lookup(hostname, options, callback) {
     all = options.all === true;
 
     if (hints !== 0 &&
-        hints !== exports.ADDRCONFIG &&
-        hints !== exports.V4MAPPED &&
-        hints !== (exports.ADDRCONFIG | exports.V4MAPPED)) {
+        hints !== cares.AI_ADDRCONFIG &&
+        hints !== cares.AI_V4MAPPED &&
+        hints !== (cares.AI_ADDRCONFIG | cares.AI_V4MAPPED)) {
       throw new TypeError('Invalid argument: hints must use valid flags');
     }
   } else {
@@ -166,7 +166,7 @@ exports.lookup = function lookup(hostname, options, callback) {
 
   callback.immediately = true;
   return req;
-};
+}
 
 
 function onlookupservice(err, host, service) {
@@ -178,7 +178,7 @@ function onlookupservice(err, host, service) {
 
 
 // lookupService(address, port, callback)
-exports.lookupService = function lookupService(host, port, callback) {
+function lookupService(host, port, callback) {
   if (arguments.length !== 3)
     throw new Error('Invalid arguments');
 
@@ -205,7 +205,7 @@ exports.lookupService = function lookupService(host, port, callback) {
 
   callback.immediately = true;
   return req;
-};
+}
 
 
 function onresolve(err, result, ttls) {
@@ -251,26 +251,25 @@ function resolver(bindingName) {
 
 
 var resolveMap = Object.create(null);
-exports.resolve4 = resolveMap.A = resolver('queryA');
-exports.resolve6 = resolveMap.AAAA = resolver('queryAaaa');
-exports.resolveCname = resolveMap.CNAME = resolver('queryCname');
-exports.resolveMx = resolveMap.MX = resolver('queryMx');
-exports.resolveNs = resolveMap.NS = resolver('queryNs');
-exports.resolveTxt = resolveMap.TXT = resolver('queryTxt');
-exports.resolveSrv = resolveMap.SRV = resolver('querySrv');
-exports.resolvePtr = resolveMap.PTR = resolver('queryPtr');
-exports.resolveNaptr = resolveMap.NAPTR = resolver('queryNaptr');
-exports.resolveSoa = resolveMap.SOA = resolver('querySoa');
-exports.reverse = resolver('getHostByAddr');
-
-
-exports.resolve = function resolve(hostname, type_, callback_) {
+resolveMap.A = resolver('queryA');
+resolveMap.AAAA = resolver('queryAaaa');
+resolveMap.CNAME = resolver('queryCname');
+resolveMap.MX = resolver('queryMx');
+resolveMap.NS = resolver('queryNs');
+resolveMap.TXT = resolver('queryTxt');
+resolveMap.SRV = resolver('querySrv');
+resolveMap.PTR = resolver('queryPtr');
+resolveMap.NAPTR = resolver('queryNaptr');
+resolveMap.SOA = resolver('querySoa');
+
+
+function resolve(hostname, type_, callback_) {
   var resolver, callback;
   if (typeof type_ === 'string') {
     resolver = resolveMap[type_];
     callback = callback_;
   } else if (typeof type_ === 'function') {
-    resolver = exports.resolve4;
+    resolver = resolveMap.A;
     callback = type_;
   } else {
     throw new Error('"type" argument must be a string');
@@ -281,15 +280,15 @@ exports.resolve = function resolve(hostname, type_, callback_) {
   } else {
     throw new Error(`Unknown type "${type_}"`);
   }
-};
+}
 
 
-exports.getServers = function getServers() {
+function getServers() {
   return cares.getServers();
-};
+}
 
 
-exports.setServers = function setServers(servers) {
+function setServers(servers) {
   // cache the original servers because in the event of an error setting the
   // servers cares won't have any servers available for resolution
   const orig = cares.getServers();
@@ -326,34 +325,53 @@ exports.setServers = function setServers(servers) {
     var err = cares.strerror(errorNumber);
     throw new Error(`c-ares failed to set servers: "${err}" [${servers}]`);
   }
-};
+}
 
-// uv_getaddrinfo flags
-exports.ADDRCONFIG = cares.AI_ADDRCONFIG;
-exports.V4MAPPED = cares.AI_V4MAPPED;
-
-// ERROR CODES
-exports.NODATA = 'ENODATA';
-exports.FORMERR = 'EFORMERR';
-exports.SERVFAIL = 'ESERVFAIL';
-exports.NOTFOUND = 'ENOTFOUND';
-exports.NOTIMP = 'ENOTIMP';
-exports.REFUSED = 'EREFUSED';
-exports.BADQUERY = 'EBADQUERY';
-exports.BADNAME = 'EBADNAME';
-exports.BADFAMILY = 'EBADFAMILY';
-exports.BADRESP = 'EBADRESP';
-exports.CONNREFUSED = 'ECONNREFUSED';
-exports.TIMEOUT = 'ETIMEOUT';
-exports.EOF = 'EOF';
-exports.FILE = 'EFILE';
-exports.NOMEM = 'ENOMEM';
-exports.DESTRUCTION = 'EDESTRUCTION';
-exports.BADSTR = 'EBADSTR';
-exports.BADFLAGS = 'EBADFLAGS';
-exports.NONAME = 'ENONAME';
-exports.BADHINTS = 'EBADHINTS';
-exports.NOTINITIALIZED = 'ENOTINITIALIZED';
-exports.LOADIPHLPAPI = 'ELOADIPHLPAPI';
-exports.ADDRGETNETWORKPARAMS = 'EADDRGETNETWORKPARAMS';
-exports.CANCELLED = 'ECANCELLED';
+module.exports = {
+  lookup,
+  lookupService,
+  getServers,
+  setServers,
+  resolve,
+  resolve4: resolveMap.A,
+  resolve6: resolveMap.AAAA,
+  resolveCname: resolveMap.CNAME,
+  resolveMx: resolveMap.MX,
+  resolveNs: resolveMap.NS,
+  resolveTxt: resolveMap.TXT,
+  resolveSrv: resolveMap.SRV,
+  resolvePtr: resolveMap.PTR,
+  resolveNaptr: resolveMap.NAPTR,
+  resolveSoa: resolveMap.SOA,
+  reverse: resolver('getHostByAddr'),
+
+  // uv_getaddrinfo flags
+  ADDRCONFIG: cares.AI_ADDRCONFIG,
+  V4MAPPED: cares.AI_V4MAPPED,
+
+  // ERROR CODES
+  NODATA: 'ENODATA',
+  FORMERR: 'EFORMERR',
+  SERVFAIL: 'ESERVFAIL',
+  NOTFOUND: 'ENOTFOUND',
+  NOTIMP: 'ENOTIMP',
+  REFUSED: 'EREFUSED',
+  BADQUERY: 'EBADQUERY',
+  BADNAME: 'EBADNAME',
+  BADFAMILY: 'EBADFAMILY',
+  BADRESP: 'EBADRESP',
+  CONNREFUSED: 'ECONNREFUSED',
+  TIMEOUT: 'ETIMEOUT',
+  EOF: 'EOF',
+  FILE: 'EFILE',
+  NOMEM: 'ENOMEM',
+  DESTRUCTION: 'EDESTRUCTION',
+  BADSTR: 'EBADSTR',
+  BADFLAGS: 'EBADFLAGS',
+  NONAME: 'ENONAME',
+  BADHINTS: 'EBADHINTS',
+  NOTINITIALIZED: 'ENOTINITIALIZED',
+  LOADIPHLPAPI: 'ELOADIPHLPAPI',
+  ADDRGETNETWORKPARAMS: 'EADDRGETNETWORKPARAMS',
+  CANCELLED: 'ECANCELLED'
+};