dns: implement light dns caching

lib/dns.js

@@ -31,6 +31,7 @@ const cares = internalBinding('cares_wrap');
 const { isIP } = require('internal/net');
 const { customPromisifyArgs } = require('internal/util');
 const errors = require('internal/errors');
+const { setTimeout, unref } = require('timers');
 const {
   bindDefaultResolver,
   setDefaultResolver,
@@ -133,16 +134,48 @@ function onlookupall(err, addresses) {
   }
 }
 
+function cleanDnsCache() {
+  for (const key in dnsCache) {
+    delete dnsCache[key];
+  }
+}
+
+function scheduleCleanup() {
+  if (cleanupTimeout) {
+    return;
+  }
+
+  cleanupTimeout = setTimeout(() => {
+    cleanDnsCache();
+    cleanupTimeout = null;
+  }, 1000).ref();
+}
+
+function addDnsEntry(cacheKey, address, family) {
+  dnsCache[cacheKey] = {
+    address,
+    family,
+    timestamp: DateNow(),
+  };
+
+  scheduleCleanup();
+
+  return dnsCache[cacheKey];
+}
 
 // Easy DNS A/AAAA look up
 // lookup(hostname, [options,] callback)
 const validFamilies = [0, 4, 6];
+const dnsCache = { __proto__: null };
+const { DateNow } = primordials;
+let cleanupTimeout = null;
 function lookup(hostname, options, callback) {
   let hints = 0;
   let family = 0;
   let all = false;
   let verbatim = getDefaultVerbatim();
 
+
   // Parse arguments
   if (hostname) {
     validateString(hostname, 'hostname');
@@ -212,8 +245,22 @@ function lookup(hostname, options, callback) {
     return {};
   }
 
+  const cacheKey = `${hostname}_${family || 'default'}`;
+  const cachedResult = dnsCache[cacheKey];
+
+  if (cachedResult && DateNow() - cachedResult.timestamp < 1000) {
+    callback(null, cachedResult.address, cachedResult.family);
+    return {};
+  }
+
+
   const req = new GetAddrInfoReqWrap();
-  req.callback = callback;
+  req.callback = (error, address, family) => {
+    if (!error) {
+      addDnsEntry(cacheKey, address, family);
+    }
+    callback(error, address, family);
+  };
   req.family = family;
   req.hostname = hostname;
   req.oncomplete = all ? onlookupall : onlookup;