http: remove stale timeout listeners

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.on('response', (r) => {
+      r.on('end', () => {
+        socket.removeListener('timeout', emitRequestTimeout);
+      });
+    });
   }
   req.emit('socket', socket);
 }

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

@@ -0,0 +1,55 @@
+'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: 100
+};
+
+process.on('unhandledRejection', function(reason) {
+  common.fail('A promise rejection was unhandled: ' + reason);
+});
+
+server.listen(0, options.host, (e) => {
+  options.port = server.address().port;
+
+  doRequest().then(doRequest)
+    .then((numListeners) => {
+      assert.strictEqual(numListeners, 1);
+      server.close();
+      agent.destroy();
+    });
+});
+
+function doRequest() {
+  return new Promise((resolve, reject) => {
+    http.request(options, (response) => {
+      const sockets = agent.sockets[`${options.host}:${options.port}:`];
+      if (sockets.length !== 1) {
+        reject(new Error('Only one socket should be created'));
+      }
+      const socket = sockets[0];
+      const timeoutEvent = socket._events.timeout;
+      let numListeners = 0;
+      if (Array.isArray(timeoutEvent)) {
+        numListeners = timeoutEvent.length;
+      } else if (timeoutEvent) {
+        numListeners = 1;
+      }
+      response.resume();
+      response.on('end', () => resolve(numListeners));
+    }).end();
+  });
+}