Re-introduce fetchImpl.

Author: taeold

packages/functions/src/service.ts

@@ -106,7 +106,8 @@ export class FunctionsService implements _FirebaseService {
     authProvider: Provider<FirebaseAuthInternalName>,
     messagingProvider: Provider<MessagingInternalComponentName>,
     appCheckProvider: Provider<AppCheckInternalComponentName>,
-    regionOrCustomDomain: string = DEFAULT_REGION
+    regionOrCustomDomain: string = DEFAULT_REGION,
+    readonly fetchImpl: typeof fetch = fetch,
   ) {
     this.contextProvider = new ContextProvider(
       authProvider,
@@ -224,13 +225,14 @@ export function httpsCallableFromURL<RequestData, ResponseData, StreamData = unk
 async function postJSON(
   url: string,
   body: unknown,
-  headers: { [key: string]: string }
+  headers: { [key: string]: string },
+  fetchImpl: typeof fetch
 ): Promise<HttpResponse> {
   headers['Content-Type'] = 'application/json';
 
   let response: Response;
   try {
-    response = await fetch(url, {
+    response = await fetchImpl(url, {
       method: 'POST',
       body: JSON.stringify(body),
       headers
@@ -308,7 +310,7 @@ async function callAtURL(
 
   const failAfterHandle = failAfter(timeout);
   const response = await Promise.race([
-    postJSON(url, body, headers),
+    postJSON(url, body, headers, functionsInstance.fetchImpl),
     failAfterHandle.promise,
     functionsInstance.cancelAllRequests
   ]);
@@ -364,7 +366,7 @@ function stream(
   options?: HttpsCallableStreamOptions
 ): Promise<HttpsCallableStreamResult> {
   const url = functionsInstance._url(name);
-  return streamAtURL(functionsInstance, url, options);
+  return streamAtURL(functionsInstance, url, data, options);
 }
 
 /**
@@ -401,7 +403,7 @@ async function streamAtURL(
 
   let response: Response;
   try {
-    response = await fetch(url, {
+    response = await functionsInstance.fetchImpl(url, {
       method: 'POST',
       body: JSON.stringify(body),
       headers,
@@ -458,7 +460,6 @@ async function streamAtURL(
     resultRejecter = reject;
   });
 
-  // Set up abort handler for the stream
   options?.signal?.addEventListener('abort', () => {
     reader.cancel();
     const error = new FunctionsError(