http: remove stale timeout listeners

In order to prevent a memory leak when using keep alive, ensure that the
timeout listener for the request is removed when the response has ended.

PR-URL: #9440
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/_http_client.js

@@ -562,7 +562,13 @@ function tickOnSocket(req, socket) {
   socket.on('close', socketCloseListener);
 
   if (req.timeout) {
-    socket.once('timeout', () => req.emit('timeout'));
+    const emitRequestTimeout = () => req.emit('timeout');
+    socket.once('timeout', emitRequestTimeout);
+    req.once('response', (res) => {
+      res.once('end', () => {
+        socket.removeListener('timeout', emitRequestTimeout);
+      });
+    });
   }
   req.emit('socket', socket);
 }

test/parallel/test-http-client-timeout-option-listeners.js

@@ -0,0 +1,44 @@
+'use strict';
+const common = require('../common');
+const http = require('http');
+const assert = require('assert');
+
+const agent = new http.Agent({ keepAlive: true });
+
+const server = http.createServer((req, res) => {
+  res.end('');
+});
+
+const options = {
+  agent,
+  method: 'GET',
+  port: undefined,
+  host: common.localhostIPv4,
+  path: '/',
+  timeout: common.platformTimeout(100)
+};
+
+server.listen(0, options.host, common.mustCall(() => {
+  options.port = server.address().port;
+  doRequest(common.mustCall((numListeners) => {
+    assert.strictEqual(numListeners, 1);
+    doRequest(common.mustCall((numListeners) => {
+      assert.strictEqual(numListeners, 1);
+      server.close();
+      agent.destroy();
+    }));
+  }));
+}));
+
+function doRequest(cb) {
+  http.request(options, common.mustCall((response) => {
+    const sockets = agent.sockets[`${options.host}:${options.port}:`];
+    assert.strictEqual(sockets.length, 1);
+    const socket = sockets[0];
+    const numListeners = socket.listeners('timeout').length;
+    response.resume();
+    response.once('end', common.mustCall(() => {
+      process.nextTick(cb, numListeners);
+    }));
+  })).end();
+}