dns: add custom timeout.

lib/net/dns.js

@@ -31,7 +31,7 @@ exports.resolve = function resolve(host, proxy) {
     return socks.resolve(proxy, host);
 
   return new Promise((resolve, reject) => {
-    dns.resolve(host, 'A', (err, result) => {
+    dns.resolve(host, 'A', to((err, result) => {
       if (err) {
         reject(err);
         return;
@@ -43,7 +43,7 @@ exports.resolve = function resolve(host, proxy) {
       }
 
       resolve(result);
-    });
+    }));
   });
 };
 
@@ -61,7 +61,7 @@ exports.lookup = function lookup(host, proxy) {
   return new Promise((resolve, reject) => {
     let addrs = [];
 
-    dns.lookup(host, options, (err, result) => {
+    dns.lookup(host, options, to((err, result) => {
       if (err) {
         reject(err);
         return;
@@ -76,6 +76,24 @@ exports.lookup = function lookup(host, proxy) {
         addrs.push(addr.address);
 
       resolve(addrs);
-    });
+    }));
   });
 };
+
+/*
+ * Helpers
+ */
+
+function to(callback) {
+  let timeout = setTimeout(() => {
+    callback(new Error('DNS request timed out.'));
+    callback = null;
+  }, 5000);
+
+  return function(err, result) {
+    if (callback) {
+      clearTimeout(timeout);
+      callback(err, result);
+    }
+  };
+}