Added functionality to pass custom fetch to rest data source

This is an optional constructor parameter. If a custom fetch function is not defined, the default fetch will be used.

This new functionality has been covered in the http cache tests.

Co-Authored-By: Jae Anne Bach Hardie <j@limina.net>

packages/apollo-datasource-rest/src/HTTPCache.ts

@@ -6,7 +6,10 @@ import { KeyValueCache, InMemoryLRUCache } from 'apollo-server-caching';
 import { CacheOptions } from './RESTDataSource';
 
 export class HTTPCache {
-  constructor(private keyValueCache: KeyValueCache = new InMemoryLRUCache()) {}
+  constructor(
+    private keyValueCache: KeyValueCache = new InMemoryLRUCache(),
+    private httpFetch: typeof fetch = fetch,
+  ) {}
 
   async fetch(
     request: Request,
@@ -21,7 +24,7 @@ export class HTTPCache {
 
     const entry = await this.keyValueCache.get(`httpcache:${cacheKey}`);
     if (!entry) {
-      const response = await fetch(request);
+      const response = await this.httpFetch(request);
 
       const policy = new CachePolicy(
         policyRequestFrom(request),
@@ -61,7 +64,7 @@ export class HTTPCache {
       const revalidationRequest = new Request(request, {
         headers: revalidationHeaders,
       });
-      const revalidationResponse = await fetch(revalidationRequest);
+      const revalidationResponse = await this.httpFetch(revalidationRequest);
 
       const { policy: revalidatedPolicy, modified } = policy.revalidatedPolicy(
         policyRequestFrom(revalidationRequest),

packages/apollo-datasource-rest/src/RESTDataSource.ts

@@ -7,6 +7,7 @@ import {
   URL,
   URLSearchParams,
   URLSearchParamsInit,
+  fetch,
 } from 'apollo-server-env';
 
 import { DataSource, DataSourceConfig } from 'apollo-datasource';
@@ -48,9 +49,13 @@ export abstract class RESTDataSource<TContext = any> extends DataSource {
   context!: TContext;
   memoizedResults = new Map<string, Promise<any>>();
 
+  constructor(private httpFetch?: typeof fetch) {
+    super();
+  }
+
   initialize(config: DataSourceConfig<TContext>): void {
     this.context = config.context;
-    this.httpCache = new HTTPCache(config.cache);
+    this.httpCache = new HTTPCache(config.cache, this.httpFetch);
   }
 
   baseURL?: string;

packages/apollo-datasource-rest/src/__tests__/HTTPCache.test.ts

@@ -452,4 +452,18 @@ describe('HTTPCache', () => {
     expect(await response2.json()).toEqual({ name: 'Alan Turing' });
     expect(response2.headers.get('Age')).toEqual('10');
   });
+
+  it('fetches a response from the origin with a custom fetch function', async () => {
+    fetch.mockJSONResponseOnce({ name: 'Ada Lovelace' });
+
+    const customFetch = jest.fn(fetch);
+    const customHttpCache = new HTTPCache(store as any, customFetch);
+
+    const response = await customHttpCache.fetch(
+      new Request('https://api.example.com/people/1'),
+    );
+
+    expect(customFetch.mock.calls.length).toEqual(1);
+    expect(await response.json()).toEqual({ name: 'Ada Lovelace' });
+  });
 });