update redirect handling on forwarded action requests (#65097)

If a forwarded server action redirects, don't attempt to follow the
redirect as it can lead to errors. For example, if the forwarded request
followed a redirect to the same URL and had to forward the request
again, it'd hit a loop. The redirect will be handled by the
`X-Action-Redirect` which will be set when the forwarded action hits the
`createRedirectRenderResult` case.

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Closes NEXT-3243

packages/next/src/server/app-render/action-handler.ts

@@ -206,6 +206,7 @@ async function createForwardedActionResponse(
       body,
       duplex: 'half',
       headers: forwardedHeaders,
+      redirect: 'manual',
       next: {
         // @ts-ignore
         internal: 1,
@@ -226,9 +227,11 @@ async function createForwardedActionResponse(
       response.body?.cancel()
     }
   } catch (err) {
-    // we couldn't stream the forwarded response, so we'll just do a normal redirect
+    // we couldn't stream the forwarded response, so we'll just return an empty response
     console.error(`failed to forward action response`, err)
   }
+
+  return RenderResult.fromStatic('{}')
 }
 
 async function createRedirectRenderResult(

test/e2e/app-dir/actions/app-action.test.ts

@@ -598,6 +598,40 @@ describe('app-dir action handling', () => {
     }
   )
 
+  it.each(['node', 'edge'])(
+    'should not error when a forwarded action triggers a redirect (%s)',
+    async (runtime) => {
+      let redirectResponseCode
+      const browser = await next.browser(`/delayed-action/${runtime}`, {
+        beforePageLoad(page) {
+          page.on('response', async (res: Response) => {
+            const headers = await res.allHeaders()
+            if (headers['x-action-redirect']) {
+              redirectResponseCode = res.status()
+            }
+          })
+        },
+      })
+
+      // Trigger the delayed action. This will sleep for a few seconds before dispatching the server action handler
+      await browser.elementById('run-action-redirect').click()
+
+      // navigate away from the page
+      await browser
+        .elementByCss(`[href='/delayed-action/${runtime}/other']`)
+        .click()
+        .waitForElementByCss('#other-page')
+
+      // confirm a successful response code on the redirected action
+      await retry(async () => {
+        expect(redirectResponseCode).toBe(200)
+      })
+
+      // confirm that the redirect was handled
+      await browser.waitForElementByCss('#run-action-redirect')
+    }
+  )
+
   if (isNextStart) {
     it('should not expose action content in sourcemaps', async () => {
       const sourcemap = (

test/e2e/app-dir/actions/app/delayed-action/actions.ts

@@ -1,8 +1,15 @@
 'use server'
 import { revalidatePath } from 'next/cache'
+import { redirect } from 'next/navigation'
 
 export const action = async () => {
   console.log('revalidating')
   revalidatePath('/delayed-action', 'page')
   return Math.random()
 }
+
+export const redirectAction = async () => {
+  // sleep for 500ms
+  await new Promise((res) => setTimeout(res, 500))
+  redirect('/delayed-action/node')
+}

test/e2e/app-dir/actions/app/delayed-action/button.tsx

@@ -1,7 +1,7 @@
 'use client'
 
 import { useContext } from 'react'
-import { action } from './actions'
+import { action, redirectAction } from './actions'
 import { DataContext } from './context'
 
 export function Button() {
@@ -13,9 +13,24 @@ export function Button() {
 
     setData(result)
   }
+
+  const handleRedirect = async () => {
+    await new Promise((res) => setTimeout(res, 1000))
+
+    const result = await redirectAction()
+
+    setData(result)
+  }
+
   return (
-    <button onClick={handleClick} id="run-action">
-      Run Action
-    </button>
+    <>
+      <button onClick={handleClick} id="run-action">
+        Run Action
+      </button>
+
+      <button onClick={handleRedirect} id="run-action-redirect">
+        Run Redirect
+      </button>
+    </>
   )
 }