http: do not leak error listeners

lib/_http_server.js

@@ -762,7 +762,10 @@ const requestHeaderFieldsTooLargeResponse = Buffer.from(
 function socketOnError(e) {
   // Ignore further errors
   this.removeListener('error', socketOnError);
-  this.on('error', noop);
+
+  if (!this.listenerCount('error') === 0) {
+    this.on('error', noop);
+  }
 
   if (!this.server.emit('clientError', e, this)) {
     if (this.writable && this.bytesWritten === 0) {

test/parallel/test-http-socket-listeners.js

@@ -0,0 +1,44 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+const net = require('net');
+
+// This test sends an invalid character to a HTTP server and purposely
+// does not handle clientError (even if it sets an event handler).
+//
+// The idea is to let the server emit multiple errors on the socket,
+// mostly due to parsing error, and make sure they don't result
+// in leaking event listeners.
+
+let i = 0;
+let socket;
+
+process.on('warning', common.mustNotCall());
+
+const server = http.createServer(common.mustNotCall());
+
+server.on('clientError', common.mustCallAtLeast((err) => {
+  assert.strictEqual(err.code, 'HPE_INVALID_METHOD');
+  assert.strictEqual(err.rawPacket.toString(), '*');
+
+  if (i === 20) {
+    socket.end();
+  } else {
+    socket.write('*');
+    i++;
+  }
+}, 1));
+
+server.listen(0, () => {
+  socket = net.createConnection({ port: server.address().port });
+
+  socket.on('connect', () => {
+    socket.write('*');
+  });
+
+  socket.on('close', () => {
+    server.close();
+  });
+});