From 39ba118a15c7e29f4764f8ee37072a4d0612b0ba Mon Sep 17 00:00:00 2001
From: cjihrig <cjihrig@gmail.com>
Date: Thu, 18 Aug 2016 17:09:37 -0400
Subject: [PATCH 1/2] dns: lookupService() callback must be a function

lookupService() requires a callback function. This commit adds
a check to verify that the callback is actually a function.
---
 lib/dns.js                | 5 ++++-
 test/parallel/test-dns.js | 4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/dns.js b/lib/dns.js
index 8d1541718abf75..3fd5184d83f4ca 100644
--- a/lib/dns.js
+++ b/lib/dns.js
@@ -191,9 +191,12 @@ exports.lookupService = function(host, port, callback) {
   if (isIP(host) === 0)
     throw new TypeError('"host" argument needs to be a valid IP address');
 
-  if (port == null || !isLegalPort(port))
+  if (!isLegalPort(port))
     throw new TypeError(`"port" should be >= 0 and < 65536, got "${port}"`);
 
+  if (typeof callback !== 'function')
+    throw new TypeError('"callback" argument must be a function');
+
   port = +port;
   callback = makeAsync(callback);
 
diff --git a/test/parallel/test-dns.js b/test/parallel/test-dns.js
index cd5914e026d6a9..6a73371b02f0c2 100644
--- a/test/parallel/test-dns.js
+++ b/test/parallel/test-dns.js
@@ -177,3 +177,7 @@ assert.throws(function() {
 assert.throws(function() {
   dns.lookupService('0.0.0.0', 'test', noop);
 }, /"port" should be >= 0 and < 65536, got "test"/);
+
+assert.throws(() => {
+  dns.lookupService('0.0.0.0', 80, null);
+}, /^TypeError: "callback" argument must be a function$/);

From 2bebeb1bd5c2bf95dd9cd9712fd684719487ab91 Mon Sep 17 00:00:00 2001
From: cjihrig <cjihrig@gmail.com>
Date: Thu, 18 Aug 2016 17:15:37 -0400
Subject: [PATCH 2/2] dns: remove makeAsync() function check

makeAsync() is an internal method in the dns module. All of the
functions that call makeAsync() have already validated that the
callback is a function. This commit removes a redundant typeof
function check.
---
 lib/dns.js | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/lib/dns.js b/lib/dns.js
index 3fd5184d83f4ca..7c76aebb97f449 100644
--- a/lib/dns.js
+++ b/lib/dns.js
@@ -56,9 +56,6 @@ function errnoException(err, syscall, hostname) {
 //   callback.immediately = true;
 // }
 function makeAsync(callback) {
-  if (typeof callback !== 'function') {
-    return callback;
-  }
   return function asyncCallback() {
     if (asyncCallback.immediately) {
       // The API already returned, we can invoke the callback immediately.