fix: handle middleware redirects to default locale and same path (#2636)

* test: add test case for middleware redirect to same path just changing locale to defalt

* fix: don't use request locale as fallback locale for redirects

Author: pieh

edge-runtime/lib/response.ts

@@ -24,7 +24,6 @@ interface BuildResponseOptions {
   request: Request
   result: FetchEventResult
   nextConfig?: RequestData['nextConfig']
-  requestLocale?: string
 }
 
 export const buildResponse = async ({
@@ -33,7 +32,6 @@ export const buildResponse = async ({
   request,
   result,
   nextConfig,
-  requestLocale,
 }: BuildResponseOptions): Promise<Response | void> => {
   logger
     .withFields({ is_nextresponse_next: result.response.headers.has('x-middleware-next') })
@@ -197,11 +195,10 @@ export const buildResponse = async ({
     return addMiddlewareHeaders(context.rewrite(target), res)
   }
 
-  // If we are redirecting a request that had a locale in the URL, we need to add it back in
-  if (redirect && requestLocale) {
-    redirect = normalizeLocalizedTarget({ target: redirect, request, nextConfig, requestLocale })
+  if (redirect) {
+    redirect = normalizeLocalizedTarget({ target: redirect, request, nextConfig })
     if (redirect === request.url) {
-      logger.withFields({ rewrite_url: rewrite }).debug('Rewrite url is same as original url')
+      logger.withFields({ redirect_url: redirect }).debug('Redirect url is same as original url')
       return
     }
     res.headers.set('location', redirect)
@@ -234,25 +231,25 @@ function normalizeLocalizedTarget({
   target,
   request,
   nextConfig,
-  requestLocale,
 }: {
   target: string
   request: Request
   nextConfig?: RequestData['nextConfig']
-  requestLocale?: string
-}) {
+}): string {
   const targetUrl = new URL(target, request.url)
 
   const normalizedTarget = normalizeLocalePath(targetUrl.pathname, nextConfig?.i18n?.locales)
 
-  const locale = normalizedTarget.detectedLocale ?? requestLocale
   if (
-    locale &&
+    normalizedTarget.detectedLocale &&
     !normalizedTarget.pathname.startsWith(`/api/`) &&
     !normalizedTarget.pathname.startsWith(`/_next/static/`)
   ) {
     targetUrl.pathname =
-      addBasePath(`/${locale}${normalizedTarget.pathname}`, nextConfig?.basePath) || `/`
+      addBasePath(
+        `/${normalizedTarget.detectedLocale}${normalizedTarget.pathname}`,
+        nextConfig?.basePath,
+      ) || `/`
   } else {
     targetUrl.pathname = addBasePath(normalizedTarget.pathname, nextConfig?.basePath) || `/`
   }

edge-runtime/middleware.ts

@@ -61,7 +61,6 @@ export async function handleMiddleware(
       logger: reqLogger,
       request,
       result,
-      requestLocale: nextRequest.detectedLocale,
       nextConfig,
     })
 

tests/fixtures/middleware-i18n/middleware.js

@@ -81,6 +81,11 @@ export async function middleware(request) {
     return Response.redirect(new URL('/new-home#fragment', url))
   }
 
+  if (url.locale !== 'en' && url.pathname === '/redirect-to-same-page-but-default-locale') {
+    url.locale = 'en'
+    return Response.redirect(url)
+  }
+
   if (url.pathname.includes('/json')) {
     return NextResponse.json({
       requestUrlPathname: new URL(request.url).pathname,

tests/integration/edge-handler.test.ts

@@ -503,6 +503,30 @@ describe('page router', () => {
     expect(response.status).toBe(302)
   })
 
+  test<FixtureTestContext>('should support redirects to default locale without changing path', async (ctx) => {
+    await createFixture('middleware-i18n', ctx)
+    await runPlugin(ctx)
+    const origin = await LocalServer.run(async (req, res) => {
+      res.write(
+        JSON.stringify({
+          url: req.url,
+          headers: req.headers,
+        }),
+      )
+      res.end()
+    })
+    ctx.cleanup?.push(() => origin.stop())
+    const response = await invokeEdgeFunction(ctx, {
+      functions: ['___netlify-edge-handler-middleware'],
+      origin,
+      url: `/fr/redirect-to-same-page-but-default-locale`,
+      redirect: 'manual',
+    })
+    const url = new URL(response.headers.get('location') ?? '', 'http://n/')
+    expect(url.pathname).toBe('/redirect-to-same-page-but-default-locale')
+    expect(response.status).toBe(302)
+  })
+
   test<FixtureTestContext>('should preserve locale in request.nextUrl', async (ctx) => {
     await createFixture('middleware-i18n', ctx)
     await runPlugin(ctx)