http: do not rely on the 'agentRemove' event

Do not use the `'agentRemove'` event to null `socket._httpMessage` as
that event is public and can be used to not keep a request in the agent.
PR-URL: #20786Fixes: #20690
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

Author: lpinca

lib/_http_agent.js

@@ -276,7 +276,6 @@ function installListeners(agent, s, options) {
 s.removeListener('close',onClose);
 s.removeListener('free',onFree);
 s.removeListener('agentRemove',onRemove);
-s._httpMessage=null;
 }
 s.on('agentRemove',onRemove);
 }

lib/_http_client.js

@@ -459,6 +459,7 @@ function socketOnData(d) {
 socket.removeListener('close',socketCloseListener);
 socket.removeListener('error',socketErrorListener);
 
+socket._httpMessage=null;
 socket.readableFlowing=null;
 
 req.emit(eventName,res,socket,bodyHead);

test/parallel/test-http-agent-remove.js

@@ -0,0 +1,21 @@
+'use strict';
+const{ mustCall }=require('../common');
+
+consthttp=require('http');
+const{ strictEqual }=require('assert');
+
+constserver=http.createServer(mustCall((req,res)=>{
+res.flushHeaders();
+}));
+
+server.listen(0,mustCall(()=>{
+constreq=http.get({
+port: server.address().port
+},mustCall(()=>{
+const{ socket }=req;
+socket.emit('agentRemove');
+strictEqual(socket._httpMessage,req);
+socket.destroy();
+server.close();
+}));
+}));