Remove deprecation for relative URL usage in middlewares

errors/middleware-relative-urls.md

@@ -2,11 +2,11 @@
 
 #### Why This Error Occurred
 
-You are using a Middleware function that uses `Response.redirect(url)`, `NextResponse.redirect(url)` or `NextResponse.rewrite(url)` where `url` is a relative or an invalid URL. Currently this will work, but building a request with `new Request(url)` or running `fetch(url)` when `url` is a relative URL will **not** work. For this reason and to bring consistency to Next.js Middleware, this behavior will be deprecated soon in favor of always using absolute URLs.
+You are using a Middleware function that uses `Response.redirect(url)`, `NextResponse.redirect(url)` or `NextResponse.rewrite(url)` where `url` is a relative or an invalid URL. Prior to Next.js 12.1, we allowed passing relative URLs. However, constructing a request with `new Request(url)` or running `fetch(url)` when `url` is a relative URL **does not** work. For this reason and to bring consistency to Next.js Middleware, this behavior has been deprecated and now removed.
 
 #### Possible Ways to Fix It
 
-To fix this warning you must always pass absolute URL for redirecting and rewriting. There are several ways to get the absolute URL but the recommended way is to clone `NextURL` and mutate it:
+To fix this error you must always pass absolute URL for redirecting and rewriting. There are several ways to get the absolute URL but the recommended way is to clone `NextURL` and mutate it:
 
 ```typescript
 import type { NextRequest } from 'next/server'

packages/next/server/web/utils.ts

@@ -149,18 +149,16 @@ export function splitCookiesString(cookiesString: string) {
 }
 
 /**
- * We will be soon deprecating the usage of relative URLs in Middleware introducing
- * URL validation. This helper puts the future code in place and prints a warning
- * for cases where it will break. Meanwhile we preserve the previous behavior.
+ * Validate the correctness of a user-provided URL.
  */
 export function validateURL(url: string | URL): string {
   try {
     return String(new URL(String(url)))
   } catch (error: any) {
-    console.log(
-      `warn  -`,
-      'using relative URLs for Middleware will be deprecated soon - https://nextjs.org/docs/messages/middleware-relative-urls'
+    throw new Error(
+      `URLs is malformed. Please use only absolute URLs - https://nextjs.org/docs/messages/middleware-relative-urls`,
+      // @ts-expect-error This will work for people who enable the error causes polyfill
+      { cause: error }
     )
-    return String(url)
   }
 }

test/integration/middleware/core/pages/rewrites/_middleware.js

@@ -12,7 +12,7 @@ export async function middleware(request) {
   ) {
     const isExternal = url.searchParams.get('override') === 'external'
     return NextResponse.rewrite(
-      isExternal ? 'https://vercel.com' : '/rewrites/a'
+      isExternal ? 'https://vercel.com' : new URL('/rewrites/a', request.url)
     )
   }
 

test/integration/middleware/core/test/index.test.js

@@ -19,7 +19,7 @@ const context = {}
 context.appDir = join(__dirname, '../')
 
 const middlewareWarning = 'using beta Middleware (not covered by semver)'
-const urlsWarning = 'using relative URLs for Middleware will be deprecated soon'
+const urlsError = 'Please use only absolute URLs'
 
 describe('Middleware base tests', () => {
   describe('dev mode', () => {
@@ -110,7 +110,7 @@ describe('Middleware base tests', () => {
   })
 })
 
-function urlTests(log, locale = '') {
+function urlTests(_log, locale = '') {
   it('rewrites by default to a target location', async () => {
     const res = await fetchViaHTTP(context.appPort, `${locale}/urls`)
     const html = await res.text()
@@ -146,18 +146,39 @@ function urlTests(log, locale = '') {
   })
 
   it('warns when using Response.redirect with a relative URL', async () => {
-    await fetchViaHTTP(context.appPort, `${locale}/urls/relative-redirect`)
-    expect(log.output).toContain(urlsWarning)
+    const response = await fetchViaHTTP(
+      context.appPort,
+      `${locale}/urls/relative-redirect`
+    )
+    expect(await response.json()).toEqual({
+      error: {
+        message: expect.stringContaining(urlsError),
+      },
+    })
   })
 
   it('warns when using NextResponse.redirect with a relative URL', async () => {
-    await fetchViaHTTP(context.appPort, `${locale}/urls/relative-next-redirect`)
-    expect(log.output).toContain(urlsWarning)
+    const response = await fetchViaHTTP(
+      context.appPort,
+      `${locale}/urls/relative-next-redirect`
+    )
+    expect(await response.json()).toEqual({
+      error: {
+        message: expect.stringContaining(urlsError),
+      },
+    })
   })
 
-  it('warns when using NextResponse.rewrite with a relative URL', async () => {
-    await fetchViaHTTP(context.appPort, `${locale}/urls/relative-next-rewrite`)
-    expect(log.output).toContain(urlsWarning)
+  it('throws when using NextResponse.rewrite with a relative URL', async () => {
+    const response = await fetchViaHTTP(
+      context.appPort,
+      `${locale}/urls/relative-next-rewrite`
+    )
+    expect(await response.json()).toEqual({
+      error: {
+        message: expect.stringContaining(urlsError),
+      },
+    })
   })
 }