fix(ClientRequest): inherit the connection _handle for passthrough requests

src/interceptors/ClientRequest/MockHttpSocket.ts

@@ -164,7 +164,7 @@
       this.emit('error', error)
     }
 
     return super.destroy(error)
   }
 
   /**
@@ -181,6 +181,19 @@
     const socket = this.createConnection()
     this.originalSocket = socket
 
+    /**
+     * @note Inherit the original socket's connection handle.
+     * Without this, each push to the mock socket results in a
+     * new "connection" listener being added (i.e. buffering pushes).
+     * @see https://github.com/nodejs/node/blob/b18153598b25485ce4f54d0c5cb830a9457691ee/lib/net.js#L734
+     */
+    if ('_handle' in socket) {
+      Object.defineProperty(this, '_handle', {
+        value: socket._handle,
+        enumerable: true,
+      })
+    }
+
     // If the developer destroys the socket, destroy the original connection.
     this.once('error', (error) => {
       socket.destroy(error)

test/modules/http/regressions/http-max-listeners-exceeded-warning.test.ts

@@ -0,0 +1,42 @@
+// @vitest-environment node
+/**
+ * @see https://github.com/mswjs/interceptors/pull/706
+ */
+import { it, expect, beforeAll, afterAll } from 'vitest'
+import http from 'node:http'
+import { HttpServer } from '@open-draft/test-server/http'
+import { ClientRequestInterceptor } from '../../../../src/interceptors/ClientRequest'
+import { waitForClientRequest } from '../../../helpers'
+
+const httpServer = new HttpServer((app) => {
+  app.get('/', (_req, res) => {
+    // Triggers 2 reads in the MockHttpSocket
+    res.write('hello')
+    res.flushHeaders()
+    res.write(' world')
+    res.end()
+  })
+})
+
+const interceptor = new ClientRequestInterceptor()
+
+beforeAll(async () => {
+  interceptor.apply()
+  await httpServer.listen()
+})
+
+afterAll(async () => {
+  interceptor.dispose()
+  await httpServer.close()
+})
+
+it('does not buffer socket pushes for a passthrough request', async () => {
+  const request = http.get(httpServer.http.url('/'))
+  const { text } = await waitForClientRequest(request)
+
+  await expect(text()).resolves.toBe('hello world')
+  expect(
+    request.socket?.listenerCount('connect'),
+    'Must not add "connection" listeners to the socket. Those listeners mean no "_handle" exists on the mock socket.'
+  ).toBe(0)
+})