dns: use faster IP address type check on results

PR-URL: https://github.com/nodejs/node/pull/13261
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/dns.js

@@ -60,6 +60,31 @@ function errnoException(err, syscall, hostname) {
   return ex;
 }
 
+const digits = [
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0-15
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16-31
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 32-47
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, // 48-63
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 64-79
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 80-95
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 96-111
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0  // 112-127
+];
+function isIPv4(str) {
+  if (!digits[str.charCodeAt(0)]) return false;
+  if (str.length === 1) return false;
+  if (str.charCodeAt(1) === 46/*'.'*/)
+    return true;
+  else if (!digits[str.charCodeAt(1)])
+    return false;
+  if (str.length === 2) return false;
+  if (str.charCodeAt(2) === 46/*'.'*/)
+    return true;
+  else if (!digits[str.charCodeAt(2)])
+    return false;
+  return (str.length > 3 && str.charCodeAt(3) === 46/*'.'*/);
+}
+
 
 function onlookup(err, addresses) {
   if (err) {
@@ -68,25 +93,26 @@ function onlookup(err, addresses) {
   if (this.family) {
     this.callback(null, addresses[0], this.family);
   } else {
-    this.callback(null, addresses[0], addresses[0].indexOf(':') >= 0 ? 6 : 4);
+    this.callback(null, addresses[0], isIPv4(addresses[0]) ? 4 : 6);
   }
 }
 
 
 function onlookupall(err, addresses) {
-  var results = [];
   if (err) {
     return this.callback(errnoException(err, 'getaddrinfo', this.hostname));
   }
 
+  var family = this.family;
   for (var i = 0; i < addresses.length; i++) {
-    results.push({
-      address: addresses[i],
-      family: this.family || (addresses[i].indexOf(':') >= 0 ? 6 : 4)
-    });
+    const addr = addresses[i];
+    addresses[i] = {
+      address: addr,
+      family: family || (isIPv4(addr) ? 4 : 6)
+    };
   }
 
-  this.callback(null, results);
+  this.callback(null, addresses);
 }