http: detach socket from IncomingMessage on keep-alive

If the socket is not detached then a future call to res.destroy
(through e.g. pipeline) would unecessarily kill the socket while
its in the agent free list.

PR-URL: #32153
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_client.js

@@ -665,6 +665,12 @@ function responseKeepAlive(req) {
   // Mark this socket as available, AFTER user-added end
   // handlers have a chance to run.
   defaultTriggerAsyncIdScope(asyncId, process.nextTick, emitFreeNT, req);
+
+  if (req.res) {
+    // Detach socket from IncomingMessage to avoid destroying the freed
+    // socket in IncomingMessage.destroy().
+    req.res.socket = null;
+  }
 }
 
 function responseOnEnd() {

test/parallel/test-http-agent-destroyed-socket.js

@@ -48,7 +48,7 @@ const server = http.createServer(common.mustCall((req, res) => {
     response.on('end', common.mustCall(() => {
       request1.socket.destroy();
 
-      response.socket.once('close', common.mustCall(() => {
+      request1.socket.once('close', common.mustCall(() => {
         // Assert request2 was removed from the queue
         assert(!agent.requests[key]);
         process.nextTick(() => {

test/parallel/test-http-client-abort-keep-alive-destroy-res.js

@@ -0,0 +1,39 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+let socketsCreated = 0;
+
+class Agent extends http.Agent {
+  createConnection(options, oncreate) {
+    const socket = super.createConnection(options, oncreate);
+    socketsCreated++;
+    return socket;
+  }
+}
+
+const server = http.createServer((req, res) => res.end());
+
+server.listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  const agent = new Agent({
+    keepAlive: true,
+    maxSockets: 1
+  });
+
+  const req = http.get({ agent, port }, common.mustCall((res) => {
+    res.resume();
+    res.on('end', () => {
+      res.destroy();
+
+      http.get({ agent, port }, common.mustCall((res) => {
+        res.resume();
+        assert.strictEqual(socketsCreated, 1);
+        agent.destroy();
+        server.close();
+      }));
+    });
+  }));
+  req.end();
+}));