fix: don't ever execute middleware in lambda

cypress/e2e/middleware/preview.cy.ts

@@ -0,0 +1,34 @@
+describe('Preview Mode', () => {
+  it('enters and exits preview mode', () => {
+    Cypress.Cookies.debug(true)
+    cy.getCookies().then((cookie) => cy.log('cookies', cookie))
+
+    cy.intercept('/previewTest', (req) => {
+      req.continue((res) => {
+        expect(res.headers?.['x-middleware-executed']).to.equal('true')
+      })
+    }).as('previewTestVisit')
+
+    // preview mode is off by default
+    cy.visit('/previewTest')
+    cy.findByText('Is preview? No', { selector: 'h1' })
+
+    // enter preview mode
+    cy.request('/api/enterPreview').then((response) => {
+      expect(response.body).to.have.property('name', 'preview mode')
+    })
+
+    // exptected content is rendered
+    cy.visit('/previewTest')
+    cy.findByText('Is preview? Yes!', { selector: 'h1' })
+
+    // exit preview mode
+    cy.request('/api/exitPreview')
+    cy.visit('/previewTest')
+    cy.findByText('Is preview? No', { selector: 'h1' })
+
+    // we should hit /previewTest 3 times (before entering preview, after entering preview, after exiting preview)
+    // this assertion is mainly to ensure interception works and assertion on response header is made
+    cy.get('@previewTestVisit.all').should('have.length', 3)
+  })
+})

demos/middleware/middleware.ts

@@ -15,11 +15,11 @@ export async function middleware(req: NextRequest) {
     headers.set('x-hello', 'world')
     return NextResponse.next({
       request: {
-        headers
-      }
+        headers,
+      },
     })
   }
-  
+
   const request = new MiddlewareRequest(req)
 
   // skipMiddlewareUrlNormalize next config option is used so we have to try to match both html path and data blob path
@@ -41,12 +41,11 @@ export async function middleware(req: NextRequest) {
   // skipMiddlewareUrlNormalize next config option is used so we have to try to match both html path and data blob path
   if (pathname.startsWith('/request-rewrite') || pathname.endsWith('/request-rewrite.json')) {
     // request.rewrite() should return the MiddlewareResponse object instead of the Response object.
-    const res = await request.rewrite('/static-rewrite',
-    {
+    const res = await request.rewrite('/static-rewrite', {
       headers: {
         'x-rewrite-test': 'hello',
-        'x-rewrite-test-2': 'hello-2'
-      }
+        'x-rewrite-test-2': 'hello-2',
+      },
     })
     const message = `This was static (& escaping test &) but has been transformed in ${req.geo?.city}`
 
@@ -90,7 +89,7 @@ export async function middleware(req: NextRequest) {
     return response
   }
 
-  if(pathname.startsWith('/matcher-cookie')) {
+  if (pathname.startsWith('/matcher-cookie')) {
     response = NextResponse.next()
     response.cookies.set('missingCookie', 'true')
     return response
@@ -109,6 +108,13 @@ export async function middleware(req: NextRequest) {
     return response
   }
 
+  if (pathname.startsWith('/previewTest')) {
+    response = NextResponse.next()
+
+    response.headers.set('x-middleware-executed', 'true')
+    return response
+  }
+
   if (pathname.includes('locale-preserving-rewrite')) {
     return NextResponse.rewrite(new URL('/locale-test', req.url))
   }
@@ -167,8 +173,8 @@ export const config = {
     '/:all*/locale-preserving-rewrite',
     '/cookies/:path*',
     { source: '/static' },
-    {source: '/request-rewrite' },
-    { source: '/matcher-cookie'},
+    { source: '/request-rewrite' },
+    { source: '/matcher-cookie' },
     { source: '/shows/((?!99|88).*)' },
     {
       source: '/conditional',
@@ -186,8 +192,9 @@ export const config = {
         {
           type: 'cookie',
           key: 'missingCookie',
-        }
+        },
       ],
     },
+    '/previewTest',
   ],
 }

demos/middleware/pages/api/enterPreview.js

@@ -0,0 +1,6 @@
+export default async function preview(req, res) {
+  // Enable Preview Mode by setting the cookies
+  res.setPreviewData({})
+
+  res.status(200).json({ name: 'preview mode' })
+}

demos/middleware/pages/api/exitPreview.js

@@ -0,0 +1,8 @@
+export default async function exit(_, res) {
+  // Exit the current user from "Preview Mode". This function accepts no args.
+  res.clearPreviewData()
+
+  // Redirect the user back to the index page.
+  res.writeHead(307, { Location: '/' })
+  res.end()
+}

demos/middleware/pages/index.js

@@ -48,6 +48,9 @@ export default function Home() {
         <p>
           <Link href="/headers">Adds `x-hello` request header to a rewrite</Link>
         </p>
+        <p>
+          <Link href="/previewTest">Preview mode</Link>
+        </p>
       </main>
     </div>
   )

demos/middleware/pages/previewTest.js

@@ -0,0 +1,25 @@
+import Link from 'next/link'
+
+const StaticTest = ({ isPreview }) => {
+  return (
+    <div>
+      <h1>Is preview? {isPreview ? 'Yes!' : 'No'}</h1>
+      <p>
+        <a href={isPreview ? '/api/exitPreview' : '/api/enterPreview'}>
+          {isPreview ? 'Exit Preview' : 'Enter Preview'}
+        </a>
+      </p>
+      <Link href="/">Go back home</Link>
+    </div>
+  )
+}
+
+export const getStaticProps = async ({ preview }) => {
+  return {
+    props: {
+      isPreview: Boolean(preview),
+    },
+  }
+}
+
+export default StaticTest

packages/runtime/src/templates/server.ts

@@ -18,6 +18,7 @@ interface NetlifyConfig {
   revalidateToken?: string
 }
 
+// eslint-disable-next-line max-lines-per-function
 const getNetlifyNextServer = (NextServer: NextServerType) => {
   class NetlifyNextServer extends NextServer {
     private netlifyConfig: NetlifyConfig
@@ -118,6 +119,13 @@ const getNetlifyNextServer = (NextServer: NextServerType) => {
       }
     }
 
+    // eslint-disable-next-line class-methods-use-this, require-await
+    async runMiddleware(): Promise<{ finished: boolean }> {
+      return {
+        finished: false,
+      }
+    }
+
     private getNetlifyPathsForRoute(route: string): string[] {
       const { i18n } = this.nextConfig
       const { routes, dynamicRoutes } = this.netlifyPrerenderManifest