From cf3adb735d8bae5884424ee7b9da5ed8f68971f6 Mon Sep 17 00:00:00 2001
From: Shane Myrick <shane@apollographql.com>
Date: Tue, 19 Nov 2024 13:27:05 -0800
Subject: [PATCH] Add metadata if response came from cache (#371)

Add metadata if response came from cache
---
 .changeset/long-experts-chew.md |  5 +++++
 package.json                    |  1 +
 src/HTTPCache.ts                |  7 ++++++-
 src/__tests__/HTTPCache.test.ts | 10 +++++++---
 4 files changed, 19 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/long-experts-chew.md

diff --git a/.changeset/long-experts-chew.md b/.changeset/long-experts-chew.md
new file mode 100644
index 0000000..91a88ad
--- /dev/null
+++ b/.changeset/long-experts-chew.md
@@ -0,0 +1,5 @@
+---
+'@apollo/datasource-rest': minor
+---
+
+Add metadata if response came from cache
diff --git a/package.json b/package.json
index 9229ab1..21927cb 100644
--- a/package.json
+++ b/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"
   },
diff --git a/src/HTTPCache.ts b/src/HTTPCache.ts
index fda4a56..d4ffee5 100644
--- a/src/HTTPCache.ts
+++ b/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
diff --git a/src/__tests__/HTTPCache.test.ts b/src/__tests__/HTTPCache.test.ts
index 0f6b255..8a9e66a 100644
--- a/src/__tests__/HTTPCache.test.ts
+++ b/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', () => {