http: fix http agent keep alive

lib/_http_agent.js

@@ -342,7 +342,11 @@ Agent.prototype.createSocket = function createSocket(req, options, cb) {
     installListeners(this, s, options);
     cb(null, s);
   });
-
+  // When keepAlive is true, pass the related options to createConnection
+  if (this.keepAlive) {
+    options.keepAlive = this.keepAlive;
+    options.keepAliveInitialDelay = this.keepAliveMsecs;
+  }
   const newSocket = this.createConnection(options, oncreate);
   if (newSocket)
     oncreate(null, newSocket);

test/parallel/test-http-agent-keepalive-delay.js

@@ -0,0 +1,56 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+const Agent = require('_http_agent').Agent;
+
+const agent = new Agent({
+  keepAlive: true,
+  keepAliveMsecs: 1000,
+});
+
+const server = http.createServer(common.mustCall((req, res) => {
+  res.end('ok');
+}));
+
+server.listen(0, common.mustCall(() => {
+  const createConnection = agent.createConnection;
+  agent.createConnection = (options, ...args) => {
+    assert.strictEqual(options.keepAlive, true);
+    assert.strictEqual(options.keepAliveInitialDelay, agent.keepAliveMsecs);
+    return createConnection.call(agent, options, ...args);
+  };
+  http.get({
+    host: 'localhost',
+    port: server.address().port,
+    agent: agent,
+    path: '/'
+  }, common.mustCall((res) => {
+    // for emit end event
+    res.on('data', () => {});
+    res.on('end', () => {
+      server.close();
+    });
+  }));
+}));