vercel · ijjk · Nov 1, 2023 · Oct 30, 2023 · Oct 31, 2023 · Oct 31, 2023
diff --git a/packages/next/src/server/base-server.ts b/packages/next/src/server/base-server.ts
@@ -1491,6 +1491,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       return
     }
     const { req, res } = ctx
+    const originalStatus = res.statusCode
     const { body, type } = payload
     let { revalidate } = payload
     if (!res.sent) {
@@ -1502,13 +1503,14 @@ export default abstract class Server<ServerOptions extends Options = Options> {
         revalidate = undefined
       }
 
-      return this.sendRenderResult(req, res, {
+      await this.sendRenderResult(req, res, {
         result: body,
         type,
         generateEtags,
         poweredByHeader,
         revalidate,
       })
+      res.statusCode = originalStatus
     }
   }
 

diff --git a/test/production/app-dir-prevent-304-caching/app/layout.js b/test/production/app-dir-prevent-304-caching/app/layout.js
@@ -0,0 +1,7 @@
+export default function Layout({ children }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}
diff --git a/test/production/app-dir-prevent-304-caching/app/page.js b/test/production/app-dir-prevent-304-caching/app/page.js
@@ -0,0 +1,9 @@
+export default async function Page() {
+  const time = await new Promise((resolve) => {
+    setTimeout(500, resolve(new Date().getTime()))
+  })
+
+  return <div>Time: {time}</div>
+}
+
+export const revalidate = 1
diff --git a/test/production/app-dir-prevent-304-caching/index.test.ts b/test/production/app-dir-prevent-304-caching/index.test.ts
@@ -0,0 +1,60 @@
+import { createNext, FileRef } from 'e2e-utils'
+import { NextInstance } from 'test/lib/next-modes/base'
+import { join } from 'path'
+import { fetchViaHTTP, waitFor } from 'next-test-utils'
+
+describe('app-dir-prevent-304-caching', () => {
+  let next: NextInstance
+
+  beforeAll(async () => {
+    next = await createNext({
+      files: {
+        'next.config.js': new FileRef(join(__dirname, 'next.config.js')),
+        app: new FileRef(join(__dirname, 'app')),
+      },
+    })
+  })
+  afterAll(() => next.destroy())
+
+  // https://github.com/vercel/next.js/issues/56580
+  it('should not cache 304 status', async () => {
+    // Fresh call
+    const rFresh = await fetchViaHTTP(next.url, '/')
+    expect(rFresh.status).toBe(200)
+
+    await waitFor(500)
+
+    // Cache HIT but still 200
+    const rHit = await fetchViaHTTP(
+      next.url,
+      '/',
+      {},
+      {
+        headers: {
+          'If-None-Match': rFresh.headers.get('etag'),
+        },
+      }
+    )
+    expect(rHit.status).toBe(200)
+    await waitFor(500)
+
+    // Here happens the race condition
+    const r304 = await fetchViaHTTP(
+      next.url,
+      '/',
+      {},
+      {
+        headers: {
+          'If-None-Match': rHit.headers.get('etag'),
+        },
+      }
+    )
+    expect(r304.status).toBe(304)
+    // ... Postponed but should not save 304 ...
+    await waitFor(1000)
+
+    // Now without cache headers should 200
+    const rStillFresh = await fetchViaHTTP(next.url, '/')
+    expect(rStillFresh.status).toBe(200)
+  })
+})
diff --git a/test/production/app-dir-prevent-304-caching/next.config.js b/test/production/app-dir-prevent-304-caching/next.config.js
@@ -0,0 +1,4 @@
+/** @type {import("next").NextConfig} */
+const nextConfig = {}
+
+module.exports = nextConfig