Better DNS

app/backend/dns.js

@@ -2,25 +2,33 @@ import dns from 'dns';
 import {parse as urlParse, format as urlFormat} from 'url';
 
 /**
- * Try to find a supported IPv6 address. Will throw if none found.
+ * Resolve to IP address and prefer IPv6 (only if supported)
  *
  * @param url
  * @returns {Promise}
  */
-function lookupIPv6 (url) {
+function lookup (url) {
   return new Promise((resolve, reject) => {
     const {hostname} = urlParse(url);
 
     const options = {
-      hints: dns.ADDRCONFIG,
-      family: 6,
+      hints: dns.ADDRCONFIG, // Only lookup supported addresses
+      all: true,
     };
 
     dns.lookup(hostname, options, (err, results) => {
       if (err) {
         reject(err);
+        return;
+      }
+
+      const v6 = results.find(r => r.family === 6);
+      const v4 = results.find(r => r.family === 4);
+
+      if (v6) {
+        resolve(v6.address);
       } else {
-        resolve(results);
+        resolve(v4.address);
       }
     });
   })
@@ -30,7 +38,7 @@ export async function swapHost (url) {
   let ip;
 
   try {
-    ip = await lookupIPv6(url);
+    ip = await lookup(url);
     const parsedUrl = urlParse(url);
     delete parsedUrl.host; // So it doesn't build with old host
     parsedUrl.hostname = ip;