test: add e2e case testing storing fresh responses in cdn when handli…

…ng background SWR requests

tests/e2e/page-router.test.ts

@@ -390,6 +390,63 @@ test.describe('Simple Page Router (no basePath, no i18n)', () => {
     expect(beforeFetch.localeCompare(date2)).toBeLessThan(0)
   })
 
+  test('Background SWR invocations can store fresh responses in CDN cache', async ({
+    page,
+    pageRouter,
+  }) => {
+    const slug = Date.now()
+    const pathname = `/revalidate-60/${slug}`
+
+    const beforeFirstFetch = new Date().toISOString()
+
+    const response1 = await page.goto(new URL(pathname, pageRouter.url).href)
+    expect(response1?.status()).toBe(200)
+    expect(response1?.headers()['cache-status']).toMatch(
+      /"Netlify (Edge|Durable)"; fwd=(uri-miss(; stored)?|miss)/m,
+    )
+    expect(response1?.headers()['netlify-cdn-cache-control']).toMatch(
+      /s-maxage=60, stale-while-revalidate=[0-9]+, durable/,
+    )
+
+    // ensure response was NOT produced before invocation
+    const date1 = (await page.textContent('[data-testid="date-now"]')) ?? ''
+    expect(date1.localeCompare(beforeFirstFetch)).toBeGreaterThan(0)
+
+    // allow page to get stale
+    await page.waitForTimeout(60_000)
+
+    const response2 = await page.goto(new URL(pathname, pageRouter.url).href)
+    expect(response2?.status()).toBe(200)
+    expect(response2?.headers()['cache-status']).toMatch(
+      /"Netlify (Edge|Durable)"; hit; fwd=stale/m,
+    )
+    expect(response2?.headers()['netlify-cdn-cache-control']).toMatch(
+      /s-maxage=60, stale-while-revalidate=[0-9]+, durable/,
+    )
+
+    const date2 = (await page.textContent('[data-testid="date-now"]')) ?? ''
+    expect(date2).toBe(date1)
+
+    // wait a bit to ensure background work has a chance to finish
+    // (it should take at least 5 seconds to regenerate, so we should wait at least that much to get fresh response)
+    await page.waitForTimeout(10_000)
+
+    // subsequent request should be served with fresh response from cdn cache, as previous request
+    // should result in background SWR invocation that serves fresh response that was stored in CDN cache
+    const response3 = await page.goto(new URL(pathname, pageRouter.url).href)
+    expect(response3?.status()).toBe(200)
+    expect(response3?.headers()['cache-status']).toMatch(
+      // hit, without being followed by ';fwd=stale'
+      /"Netlify (Edge|Durable)"; hit(?!; fwd=stale)/m,
+    )
+    expect(response3?.headers()['netlify-cdn-cache-control']).toMatch(
+      /s-maxage=60, stale-while-revalidate=[0-9]+, durable/,
+    )
+
+    const date3 = (await page.textContent('[data-testid="date-now"]')) ?? ''
+    expect(date3.localeCompare(date2)).toBeGreaterThan(0)
+  })
+
   test('should serve 404 page when requesting non existing page (no matching route)', async ({
     page,
     pageRouter,

tests/fixtures/page-router/netlify/functions/purge-cdn.ts

@@ -0,0 +1,41 @@
+import { purgeCache, Config } from '@netlify/functions'
+
+export default async function handler(request: Request) {
+  const url = new URL(request.url)
+  const pathToPurge = url.searchParams.get('path')
+
+  if (!pathToPurge) {
+    return Response.json(
+      {
+        status: 'error',
+        error: 'missing "path" query parameter',
+      },
+      { status: 400 },
+    )
+  }
+  try {
+    await purgeCache({ tags: [`_N_T_${encodeURI(pathToPurge)}`] })
+    return Response.json(
+      {
+        status: 'ok',
+      },
+      {
+        status: 200,
+      },
+    )
+  } catch (error) {
+    return Response.json(
+      {
+        status: 'error',
+        error: error.toString(),
+      },
+      {
+        status: 500,
+      },
+    )
+  }
+}
+
+export const config: Config = {
+  path: '/api/purge-cdn',
+}

tests/fixtures/page-router/pages/revalidate-60/[slug].js

@@ -0,0 +1,35 @@
+const Show = ({ time, easyTimeToCompare, slug }) => (
+  <div>
+    <p>
+      This page uses getStaticProps() at
+      <span data-testid="date-now">{time}</span>
+    </p>
+    <p>
+      Time string: <span data-testid="date-easy-time">{easyTimeToCompare}</span>
+    </p>
+    <p>Slug {slug}</p>
+  </div>
+)
+
+/** @type {import('next').getStaticPaths} */
+export const getStaticPaths = () => {
+  return {
+    paths: [],
+    fallback: 'blocking',
+  }
+}
+
+/** @type {import('next').GetStaticProps} */
+export async function getStaticProps({ params }) {
+  const date = new Date()
+  return {
+    props: {
+      slug: params.slug,
+      time: date.toISOString(),
+      easyTimeToCompare: date.toTimeString(),
+    },
+    revalidate: 60,
+  }
+}
+
+export default Show