Add metadata if response came from cache

.changeset/long-experts-chew.md

@@ -0,0 +1,5 @@
+---
+'@apollo/datasource-rest': minor
+---
+
+Add metadata if response came from cache

package.json

@@ -28,6 +28,7 @@
     "test:ci": "jest --coverage --ci --maxWorkers=2 --reporters=default --reporters=jest-junit",
     "watch": "tsc --build --watch",
     "lint": "eslint src/**/*.ts",
+    "changeset-add": "changeset add",
     "changeset-publish": "changeset publish",
     "changeset-check": "changeset status --verbose --since=origin/main"
   },

src/HTTPCache.ts

@@ -29,6 +29,7 @@ interface SneakyCachePolicy extends CachePolicy {
 
 interface ResponseWithCacheWritePromise {
   response: FetcherResponse;
+  responseFromCache?: Boolean;
   cacheWritePromise?: Promise<void>;
 }
 
@@ -72,7 +73,10 @@ export class HTTPCache<CO extends CacheOptions = CacheOptions> {
     // refreshing headers with HEAD requests, responding to HEADs with cached
     // and valid GETs, etc.)
     if (requestOpts.method === 'HEAD') {
-      return { response: await this.httpFetch(urlString, requestOpts) };
+      return {
+        response: await this.httpFetch(urlString, requestOpts),
+        responseFromCache: false,
+      };
     }
 
     const entry =
@@ -127,6 +131,7 @@ export class HTTPCache<CO extends CacheOptions = CacheOptions> {
           status: policy._status,
           headers: cachePolicyHeadersToNodeFetchHeadersInit(headers),
         }),
+        responseFromCache: true,
       };
     } else {
       // We aren't sure that we're allowed to use the cached response, so we are

src/__tests__/HTTPCache.test.ts

@@ -63,10 +63,12 @@ describe('HTTPCache', () => {
   it('fetches a response from the origin when not cached', async () => {
     mockGetAdaLovelace();
 
-    const { response, cacheWritePromise } = await httpCache.fetch(adaUrl);
+    const { response, responseFromCache, cacheWritePromise } =
+      await httpCache.fetch(adaUrl);
     expect(cacheWritePromise).toBeUndefined();
 
     expect(await response.json()).toEqual({ name: 'Ada Lovelace' });
+    expect(responseFromCache).toBeFalsy();
   });
 
   it('returns a cached response when not expired', async () => {
@@ -79,11 +81,12 @@ describe('HTTPCache', () => {
     await cacheWritePromise;
     jest.advanceTimersByTime(10000);
 
-    const { response } = await httpCache.fetch(adaUrl);
+    const { response, responseFromCache } = await httpCache.fetch(adaUrl);
 
     expect(response.url).toBe(adaUrl.toString());
     expect(await response.json()).toEqual({ name: 'Ada Lovelace' });
     expect(response.headers.get('age')).toEqual('10');
+    expect(responseFromCache).toBe(true);
   });
 
   it('fetches a fresh response from the origin when expired', async () => {
@@ -96,12 +99,13 @@ describe('HTTPCache', () => {
 
     mockGetAlanTuring({ 'cache-control': 'max-age=30' });
 
-    const { response } = await httpCache.fetch(
+    const { response, responseFromCache } = await httpCache.fetch(
       new URL('https://api.example.com/people/1'),
     );
 
     expect(await response.json()).toEqual({ name: 'Alan Turing' });
     expect(response.headers.get('age')).toBeNull();
+    expect(responseFromCache).toBeFalsy();
   });
 
   describe('overriding TTL', () => {