dns: implement light dns caching

lib/dns.js

@@ -137,12 +137,16 @@ function onlookupall(err, addresses) {
 // Easy DNS A/AAAA look up
 // lookup(hostname, [options,] callback)
 const validFamilies = [0, 4, 6];
+const dnsCache = { __proto__: null };
 function lookup(hostname, options, callback) {
   let hints = 0;
   let family = 0;
   let all = false;
   let verbatim = getDefaultVerbatim();
 
+  const cacheKey = `${hostname}_${family || 'default'}`;
+  const cachedResult = dnsCache[cacheKey];
+
   // Parse arguments
   if (hostname) {
     validateString(hostname, 'hostname');
@@ -191,6 +195,11 @@ function lookup(hostname, options, callback) {
     }
   }
 
+  if (cachedResult && Date.now() - cachedResult.timestamp < 1000) {
+    callback(null, cachedResult.address, cachedResult.family);
+    return {};
+  }
+
   if (!hostname) {
     emitInvalidHostnameWarning(hostname);
     if (all) {
@@ -213,7 +222,16 @@ function lookup(hostname, options, callback) {
   }
 
   const req = new GetAddrInfoReqWrap();
-  req.callback = callback;
+  req.callback = (error, address, family) => {
+    if (!error) {
+      dnsCache[cacheKey] = {
+        address,
+        family,
+        timestamp: Date.now(),
+      };
+    }
+    callback(error, address, family);
+  };
   req.family = family;
   req.hostname = hostname;
   req.oncomplete = all ? onlookupall : onlookup;
@@ -237,6 +255,16 @@ function lookup(hostname, options, callback) {
   return req;
 }
 
+// DNS cache checks every 1 second
+setInterval(() => {
+  const currentTime = Date.now();
+  for (const key in dnsCache) {
+      if (currentTime - dnsCache[key].timestamp >= 1000) {
+        delete dnsCache[key];
+      }
+  }
+}, 1000);
+
 ObjectDefineProperty(lookup, customPromisifyArgs,
                      { __proto__: null, value: ['address', 'family'], enumerable: false });