fix(cloneIncomingMessage): inherit prototype properties

src/interceptors/ClientRequest/utils/cloneIncomingMessage.test.ts

@@ -1,20 +1,25 @@
 import { Socket } from 'net'
 import { IncomingMessage } from 'http'
+import { Stream, Readable, EventEmitter } from 'stream'
 import { cloneIncomingMessage, IS_CLONE } from './cloneIncomingMessage'
 
 test('clones a given IncomingMessage', () => {
-  const source = new IncomingMessage(new Socket())
-  source.statusCode = 200
-  source.statusMessage = 'OK'
-  source.headers = { 'x-powered-by': 'msw' }
-  const clone = cloneIncomingMessage(source)
+  const message = new IncomingMessage(new Socket())
+  message.statusCode = 200
+  message.statusMessage = 'OK'
+  message.headers = { 'x-powered-by': 'msw' }
+  const clone = cloneIncomingMessage(message)
+
+  // Prototypes must be preserved.
+  expect(clone).toBeInstanceOf(IncomingMessage)
+  expect(clone).toBeInstanceOf(EventEmitter)
+  expect(clone).toBeInstanceOf(Stream)
+  expect(clone).toBeInstanceOf(Readable)
 
   expect(clone.statusCode).toEqual(200)
   expect(clone.statusMessage).toEqual('OK')
   expect(clone.headers).toHaveProperty('x-powered-by', 'msw')
 
   // Cloned IncomingMessage must be marked respectively.
   expect(clone[IS_CLONE]).toEqual(true)
-
-  expect(clone).toHaveProperty('_events')
 })

src/interceptors/ClientRequest/utils/cloneIncomingMessage.ts

@@ -7,35 +7,68 @@ export interface ClonedIncomingMessage extends IncomingMessage {
   [IS_CLONE]: boolean
 }
 
+/**
+ * Clones a given `http.IncomingMessage` instance.
+ */
 export function cloneIncomingMessage(
   message: IncomingMessage
 ): ClonedIncomingMessage {
-  const stream = message.pipe(new PassThrough())
-  const properties = [
-    ...Object.getOwnPropertyNames(message),
-    ...Object.getOwnPropertySymbols(message),
-  ] as Array<keyof IncomingMessage>
-
-  for (const propertyName of properties) {
-    if (stream.hasOwnProperty(propertyName)) {
-      continue
-    }
+  const clone = message.pipe(new PassThrough())
 
-    const propertyDescriptor = Object.getOwnPropertyDescriptor(
-      message,
-      propertyName
-    )
+  // Inherit all direct "IncomingMessage" properties.
+  inheritProperties(message, clone)
 
-    Object.defineProperty(stream, propertyName, {
-      ...propertyDescriptor,
-      value: message[propertyName],
-    })
-  }
+  // Deeply inherit the message prototypes (Readable, Stream, EventEmitter, etc.).
+  const clonedPrototype = Object.create(IncomingMessage.prototype)
+  getPrototypes(clone).forEach((prototype) => {
+    inheritProperties(prototype, clonedPrototype)
+  })
+  Object.setPrototypeOf(clone, clonedPrototype)
 
-  Object.defineProperty(stream, IS_CLONE, {
+  Object.defineProperty(clone, IS_CLONE, {
     enumerable: true,
     value: true,
   })
 
-  return stream as unknown as ClonedIncomingMessage
+  return clone as unknown as ClonedIncomingMessage
+}
+
+/**
+ * Returns a list of all prototypes the given object extends.
+ */
+function getPrototypes(source: object): object[] {
+  const prototypes: object[] = []
+  let current = source
+
+  while ((current = Object.getPrototypeOf(current))) {
+    prototypes.push(current)
+  }
+
+  return prototypes
+}
+
+/**
+ * Inherits a given target object properties and symbols
+ * onto the given source object.
+ * @param source Object which should acquire properties.
+ * @param target Object to inherit the properties from.
+ */
+function inheritProperties(source: object, target: object): void {
+  const properties = [
+    ...Object.getOwnPropertyNames(source),
+    ...Object.getOwnPropertySymbols(source),
+  ]
+
+  for (const property of properties) {
+    if (target.hasOwnProperty(property)) {
+      continue
+    }
+
+    const descriptor = Object.getOwnPropertyDescriptor(source, property)
+    if (!descriptor) {
+      continue
+    }
+
+    Object.defineProperty(target, property, descriptor)
+  }
 }