fix fetch cache for next 15

examples/app-router/app/ssr/page.tsx

@@ -14,10 +14,14 @@ async function getTime() {
 export default async function SSR() {
   const time = await getTime();
   const headerList = await headers();
+  const responseOpenNext = await fetch("https://opennext.js.org", {
+    cache: "force-cache",
+  });
   return (
     <div>
       <h1>Time: {time}</h1>
       <div> {headerList.get("host")}</div>
+      <p>Cached fetch: {responseOpenNext.headers.get("date")}</p>
     </div>
   );
 }

packages/open-next/src/adapters/cache.ts

@@ -108,6 +108,28 @@ declare global {
   var lastModified: Record<string, number>;
   var isNextAfter15: boolean;
 }
+
+function isFetchCache(
+  options?:
+    | boolean
+    | {
+        fetchCache?: boolean;
+        kindHint?: "app" | "pages" | "fetch";
+        kind?: "FETCH";
+      },
+): boolean {
+  if (typeof options === "boolean") {
+    return options;
+  }
+  if (typeof options === "object") {
+    return (
+      options.kindHint === "fetch" ||
+      options.fetchCache ||
+      options.kind === "FETCH"
+    );
+  }
+  return false;
+}
 // We need to use globalThis client here as this class can be defined at load time in next 12 but client is not available at load time
 export default class S3Cache {
   constructor(_ctx: CacheHandlerContext) {}
@@ -122,21 +144,17 @@ export default class S3Cache {
           kindHint?: "app" | "pages" | "fetch";
           tags?: string[];
           softTags?: string[];
+          kind?: "FETCH";
         },
   ) {
     if (globalThis.disableIncrementalCache) {
       return null;
     }
-    const isFetchCache =
-      typeof options === "object"
-        ? options.kindHint
-          ? options.kindHint === "fetch"
-          : options.fetchCache
-        : options;
+    const _isFetchCache = isFetchCache(options);
 
     const softTags = typeof options === "object" ? options.softTags : [];
     const tags = typeof options === "object" ? options.tags : [];
-    return isFetchCache
+    return _isFetchCache
       ? this.getFetchCache(key, softTags, tags)
       : this.getIncrementalCache(key);
   }

packages/tests-e2e/tests/appRouter/ssr.test.ts

@@ -53,3 +53,12 @@ test("Server Side Render and loading.tsx", async ({ page }) => {
   // await expect(el).toBeVisible();
   // await expect(time).not.toEqual(newTime);
 });
+
+test("Fetch cache properly cached", async ({ page }) => {
+  await page.goto("/ssr");
+  const originalDate = await page.getByText("Cached fetch:").textContent();
+  await wait(2000);
+  await page.reload();
+  const newDate = await page.getByText("Cached fetch:").textContent();
+  expect(originalDate).toEqual(newDate);
+});