fix: don't mutate route data, instead create new object to set as blob (#391)

* test: add integration test for cacheable route handler response not produced at build

* fix: don't mutate route data, instead create new object to set as blob

Author: pieh

src/run/handlers/cache.cts

@@ -159,14 +159,20 @@ export class NetlifyCacheHandler implements CacheHandler {
 
       console.debug(`[NetlifyCacheHandler.set]: ${key}`)
 
+      let value = data
+
       if (data?.kind === 'ROUTE') {
-        // @ts-expect-error gotta find a better solution for this
-        data.body = data.body.toString('base64')
+        // don't mutate data, as it's used for the initial response - instead create a new object
+        value = {
+          ...data,
+          // @ts-expect-error gotta find a better solution for this
+          body: data.body.toString('base64'),
+        }
       }
 
       await this.blobStore.setJSON(blobKey, {
         lastModified,
-        value: data,
+        value,
       })
 
       if (data?.kind === 'PAGE') {

tests/fixtures/server-components/app/api/static/[slug]/route.ts

@@ -0,0 +1,9 @@
+import { NextRequest, NextResponse } from 'next/server'
+
+export function generateStaticParams() {
+  return [{ slug: 'first' }, { slug: 'second' }]
+}
+
+export const GET = (_req: NextRequest, { params }) => {
+  return NextResponse.json({ params })
+}

tests/integration/cache-handler.test.ts

@@ -313,6 +313,8 @@ describe('plugin', () => {
     expect(blobEntries.map(({ key }) => decodeBlobKey(key)).sort()).toEqual([
       '/404',
       '/api/revalidate-handler',
+      '/api/static/first',
+      '/api/static/second',
       '/index',
       '/revalidate-fetch',
       '/static-fetch-1',
@@ -444,4 +446,13 @@ describe('route', () => {
     ).toBe(1)
     ctx.blobServerGetSpy.mockClear()
   })
+
+  test<FixtureTestContext>('cacheable route handler response not produced at build is served correctly', async (ctx) => {
+    await createFixture('server-components', ctx)
+    await runPlugin(ctx)
+
+    const call2 = await invokeFunction(ctx, { url: '/api/static/not-in-generateStaticParams' })
+
+    expect(call2.body).toBe('{"params":{"slug":"not-in-generateStaticParams"}}')
+  })
 })