fix: patch and restore Headers in interceptor

src/interceptors/ClientRequest/MockHttpSocket.ts

@@ -18,10 +18,7 @@ import {
   RESPONSE_STATUS_CODES_WITHOUT_BODY,
 } from '../../utils/responseUtils'
 import { createRequestId } from '../../createRequestId'
-import {
-  getRawFetchHeaders,
-  recordRawFetchHeaders,
-} from './utils/recordRawHeaders'
+import { getRawFetchHeaders } from './utils/recordRawHeaders'
 
 type HttpConnectionOptions = any
 
@@ -125,11 +122,6 @@ export class MockHttpSocket extends MockSocket {
       Reflect.set(this, 'getSession', () => undefined)
       Reflect.set(this, 'isSessionReused', () => false)
     }
-
-    // Spy on `Header.prototype.set` and `Header.prototype.append` calls
-    // and record the raw header names provided. This is to support
-    // `IncomingMessage.prototype.rawHeaders`.
-    recordRawFetchHeaders()
   }
 
   public emit(event: string | symbol, ...args: any[]): boolean {

src/interceptors/ClientRequest/index.ts

@@ -14,6 +14,10 @@ import { toInteractiveRequest } from '../../utils/toInteractiveRequest'
 import { normalizeClientRequestArgs } from './utils/normalizeClientRequestArgs'
 import { isNodeLikeError } from '../../utils/isNodeLikeError'
 import { createServerErrorResponse } from '../../utils/responseUtils'
+import {
+  recordRawFetchHeaders,
+  restoreHeadersPrototype,
+} from './utils/recordRawHeaders'
 
 export class ClientRequestInterceptor extends Interceptor<HttpRequestEventMap> {
   static symbol = Symbol('client-request-interceptor')
@@ -104,12 +108,19 @@ export class ClientRequestInterceptor extends Interceptor<HttpRequestEventMap> {
       },
     })
 
+    // Spy on `Header.prototype.set` and `Header.prototype.append` calls
+    // and record the raw header names provided. This is to support
+    // `IncomingMessage.prototype.rawHeaders`.
+    recordRawFetchHeaders()
+
     this.subscriptions.push(() => {
       http.get = originalGet
       http.request = originalRequest
 
       https.get = originalHttpsGet
       https.request = originalHttpsRequest
+
+      restoreHeadersPrototype()
     })
   }
 

src/interceptors/ClientRequest/utils/recordRawHeaders.ts

@@ -2,7 +2,7 @@ type HeaderTuple = [string, string]
 type RawHeaders = Array<HeaderTuple>
 
 const kRawHeaders = Symbol('kRawHeaders')
-const kHeadersPatched = Symbol('kHeadersPatched')
+const kRestoreHeaders = Symbol('kRestoreHeaders')
 
 function recordRawHeader(headers: Headers, args: HeaderTuple) {
   if (!Reflect.has(headers, kRawHeaders)) {
@@ -32,10 +32,22 @@ function recordRawHeader(headers: Headers, args: HeaderTuple) {
  * h[Symbol('headers map')] // Map { 'X-Custom' => 'one, two' }
  */
 export function recordRawFetchHeaders() {
-  if (Reflect.get(Headers.prototype.set, kHeadersPatched)) {
-    return
+  // Prevent patching the Headers prototype multiple times.
+  if (Reflect.get(Headers, kRestoreHeaders)) {
+    return Reflect.get(Headers, kRestoreHeaders)
   }
 
+  const { set, append, delete: headersDeleteMethod } = Headers.prototype
+
+  Object.defineProperty(Headers, kRestoreHeaders, {
+    value: () => {
+      Headers.prototype.set = set
+      Headers.prototype.append = append
+      Headers.prototype.delete = headersDeleteMethod
+    },
+    enumerable: false,
+  })
+
   Headers.prototype.set = new Proxy(Headers.prototype.set, {
     apply(target, thisArg, args: HeaderTuple) {
       recordRawHeader(thisArg, args)
@@ -64,8 +76,14 @@ export function recordRawFetchHeaders() {
       return Reflect.apply(target, thisArg, args)
     },
   })
+}
+
+export function restoreHeadersPrototype() {
+  if (!Reflect.get(Headers, kRestoreHeaders)) {
+    return
+  }
 
-  Reflect.set(Headers.prototype.set, kHeadersPatched, true)
+  Reflect.get(Headers, kRestoreHeaders)()
 }
 
 export function getRawFetchHeaders(headers: Headers): RawHeaders {