http: fixes memory retention issue with FreeList and HTTPParser

lib/_http_common.js

@@ -161,12 +161,10 @@ const parsers = new FreeList('parsers', 1000, function parsersCb() {
 
   cleanParser(parser);
 
-  parser.onIncoming = null;
   parser[kOnHeaders] = parserOnHeaders;
   parser[kOnHeadersComplete] = parserOnHeadersComplete;
   parser[kOnBody] = parserOnBody;
   parser[kOnMessageComplete] = parserOnMessageComplete;
-  parser[kOnTimeout] = null;
 
   return parser;
 });
@@ -232,7 +230,9 @@ function cleanParser(parser) {
   parser.outgoing = null;
   parser.maxHeaderPairs = MAX_HEADER_PAIRS;
   parser[kOnExecute] = null;
+  parser[kOnTimeout] = null;
   parser._consumed = false;
+  parser.onIncoming = null;
 }
 
 function prepareError(err, parser, rawPacket) {

test/parallel/test-http-parser-memory-retention.js

@@ -0,0 +1,42 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+const { HTTPParser } = require('_http_common');
+
+// Test that the `HTTPParser` instance is cleaned up before being returned to
+// the pool to avoid memory retention issues.
+
+const kOnTimeout = HTTPParser.kOnTimeout | 0;
+const server = http.createServer();
+
+server.on('request', common.mustCall((request, response) => {
+  const parser = request.socket.parser;
+
+  assert.strictEqual(typeof parser[kOnTimeout], 'function');
+
+  request.socket.on('close', common.mustCall(() => {
+    assert.strictEqual(parser[kOnTimeout], null);
+  }));
+
+  response.end();
+  server.close();
+}));
+
+server.listen(common.mustCall(() => {
+  const request = http.get({ port: server.address().port });
+  let parser;
+
+  request.on('socket', common.mustCall(() => {
+    parser = request.parser;
+    assert.strictEqual(typeof parser.onIncoming, 'function');
+  }));
+
+  request.on('response', common.mustCall((response) => {
+    response.resume();
+    response.on('end', common.mustCall(() => {
+      assert.strictEqual(parser.onIncoming, null);
+    }));
+  }));
+}));