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. PR-URL: #8170 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Evan Lucas <[email protected]> Reviewed-By: Yorkie Liu <[email protected]>

Author: cjihrig

lib/dns.js

@@ -191,9 +191,12 @@ exports.lookupService = function(host, port, callback){
 if(isIP(host)===0)
 thrownewTypeError('"host" argument needs to be a valid IP address');
 
-if(port==null||!isLegalPort(port))
+if(!isLegalPort(port))
 thrownewTypeError(`"port" should be >= 0 and < 65536, got "${port}"`);
 
+if(typeofcallback!=='function')
+thrownewTypeError('"callback" argument must be a function');
+
 port=+port;
 callback=makeAsync(callback);
 

test/parallel/test-dns.js

@@ -177,3 +177,7 @@ assert.throws(function(){
 assert.throws(function(){
 dns.lookupService('0.0.0.0','test',noop);
 },/"port"shouldbe>=0and<65536,got"test"/);
+
+assert.throws(()=>{
+dns.lookupService('0.0.0.0',80,null);
+},/^TypeError:"callback"argumentmustbeafunction$/);