Make it possible to pass custom fetch to rest data source (#1807)

* 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: Emily McDonald <mcdonald.emily@live.co.uk>

* Lint fix

CHANGELOG.md

@@ -222,6 +222,7 @@ the query extensions' `clientInfo` values will be used. [PR #1960](https://githu
 - Azure functions support [Issue #1752](https://github.com/apollographql/apollo-server/issue/1752) [PR #1753](https://github.com/apollographql/apollo-server/pull/1753) [PR #1948](https://github.com/apollographql/apollo-server/pull/1948)
 - Allow JSON parsing in `RESTDataSource` of Content Type `application/hal+json`. [PR #185](https://github.com/apollographql/apollo-server/pull/1853)
 - Add support for a `requestAgent` configuration parameter within the `engine` configuration.  This can be utilized when a proxy is necessary to transmit tracing and metrics data to Apollo Engine.  It accepts either an [`http.Agent`](https://nodejs.org/docs/latest-v8.x/api/http.html#http_class_http_agent) or [`https.Agent`](https://nodejs.org/docs/latest-v8.x/api/https.html#https_class_https_agent) and behaves the same as the `agent` parameter to Node.js' [`http.request`](https://nodejs.org/docs/latest-v8.x/api/http.html#http_http_request_options_callback). [PR #1879](https://github.com/apollographql/apollo-server/pull/1879)
+- Allow an optional parameter to the `RESTDataSource` constructor which takes a `node-fetch`-compatible `fetch` implementation that will be used for HTTP calls instead of the default fetch. [PR #1807](https://github.com/apollographql/apollo-server/pull/1807)
 
 ### v2.1.0
 

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

@@ -11,11 +11,17 @@ import { CacheOptions } from './RESTDataSource';
 
 export class HTTPCache {
   private keyValueCache: KeyValueCache;
-  constructor(keyValueCache: KeyValueCache = new InMemoryLRUCache()) {
+  private httpFetch: typeof fetch;
+
+  constructor(
+    keyValueCache: KeyValueCache = new InMemoryLRUCache(),
+    httpFetch: typeof fetch = fetch,
+  ) {
     this.keyValueCache = new PrefixingKeyValueCache(
       keyValueCache,
       'httpcache:',
     );
+    this.httpFetch = httpFetch;
   }
 
   async fetch(
@@ -31,7 +37,7 @@ export class HTTPCache {
 
     const entry = await this.keyValueCache.get(cacheKey);
     if (!entry) {
-      const response = await fetch(request);
+      const response = await this.httpFetch(request);
 
       const policy = new CachePolicy(
         policyRequestFrom(request),
@@ -71,7 +77,7 @@ 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,
   ValueOrPromise,
 } from 'apollo-server-env';
 
@@ -47,9 +48,13 @@ 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

@@ -459,4 +459,18 @@ 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' });
+  });
 });