Enable allowMiddlewareResponseBody by default (#44224)

Follow-up to #44195 ## Bug - [ ] Related issues linked using `fixes #number` - [ ] Integration tests added - [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md) ## Feature - [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR. - [ ] Related issues linked using `fixes #number` - [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added - [ ] Documentation added - [ ] Telemetry added. In case of a feature if it's used or not. - [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md) ## Documentation / Examples - [ ] Make sure the linting passes by running `pnpm build && pnpm lint` - [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
vercel · Dec 21, 2022 · 9ee4c0c · 9ee4c0c
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diff --git a/docs/advanced-features/middleware.md b/docs/advanced-features/middleware.md
@@ -221,18 +221,7 @@ export function middleware(request: NextRequest) {
 
 ## Producing a Response
 
-You can respond to middleware directly by returning a `NextResponse` (responding from middleware is available since Next.js v13.0.0).
-
-To enable middleware responses, update `next.config.js`:
-
-```js
-// next.config.js
-module.exports = {
-  experimental: {
-    allowMiddlewareResponseBody: true,
-  },
-}
-```
+You can respond to middleware directly by returning a `NextResponse` (responding from middleware is available since Next.js v13.1.0).
 
 Once enabled, you can provide a response from middleware using the `Response` or `NextResponse` API:
 

diff --git a/packages/next/build/webpack-config.ts b/packages/next/build/webpack-config.ts
@@ -301,9 +301,6 @@ export function getDefineEnv({
     'process.env.__NEXT_I18N_SUPPORT': JSON.stringify(!!config.i18n),
     'process.env.__NEXT_I18N_DOMAINS': JSON.stringify(config.i18n?.domains),
     'process.env.__NEXT_ANALYTICS_ID': JSON.stringify(config.analyticsId),
-    'process.env.__NEXT_ALLOW_MIDDLEWARE_RESPONSE_BODY': JSON.stringify(
-      config.allowMiddlewareResponseBody
-    ),
     'process.env.__NEXT_NO_MIDDLEWARE_URL_NORMALIZE': JSON.stringify(
       config.skipMiddlewareUrlNormalize
     ),
@@ -2062,7 +2059,6 @@ export default async function getBaseWebpackConfig(
           dev,
           sriEnabled: !dev && !!config.experimental.sri?.algorithm,
           hasFontLoaders: !!config.experimental.fontLoaders,
-          allowMiddlewareResponseBody: !!config.allowMiddlewareResponseBody,
         }),
       isClient &&
         new BuildManifestPlugin({
@@ -2154,10 +2150,6 @@ export default async function getBaseWebpackConfig(
               ['swcEmotion', !!config.compiler?.emotion],
               ['turbotrace', !!config.experimental.turbotrace],
               ['transpilePackages', !!config.transpilePackages],
-              [
-                'allowMiddlewareResponseBody',
-                !!config.allowMiddlewareResponseBody,
-              ],
               [
                 'skipMiddlewareUrlNormalize',
                 !!config.skipMiddlewareUrlNormalize,

diff --git a/packages/next/build/webpack/loaders/next-middleware-loader.ts b/packages/next/build/webpack/loaders/next-middleware-loader.ts
@@ -40,7 +40,7 @@ export default function middlewareLoader(this: any) {
   buildInfo.rootDir = rootDir
 
   return `
-        import { adapter, blockUnallowedResponse, enhanceGlobals } from 'next/dist/esm/server/web/adapter'
+        import { adapter, enhanceGlobals } from 'next/dist/esm/server/web/adapter'
 
         enhanceGlobals()
 
@@ -52,11 +52,11 @@ export default function middlewareLoader(this: any) {
         }
 
         export default function (opts) {
-          return blockUnallowedResponse(adapter({
+          return adapter({
               ...opts,
               page: ${JSON.stringify(page)},
               handler,
-          }))
+          })
         }
     `
 }
diff --git a/packages/next/build/webpack/plugins/middleware-plugin.ts b/packages/next/build/webpack/plugins/middleware-plugin.ts
@@ -232,21 +232,6 @@ function isInMiddlewareLayer(parser: webpack.javascript.JavascriptParser) {
   return parser.state.module?.layer === 'middleware'
 }
 
-function isInMiddlewareFile(parser: webpack.javascript.JavascriptParser) {
-  return (
-    parser.state.current?.layer === 'middleware' &&
-    /middleware\.\w+$/.test(parser.state.current?.rawRequest)
-  )
-}
-
-function isNullLiteral(expr: any) {
-  return expr.value === null
-}
-
-function isUndefinedIdentifier(expr: any) {
-  return expr.name === 'undefined'
-}
-
 function isProcessEnvMemberExpression(memberExpression: any): boolean {
   return (
     memberExpression.object?.type === 'Identifier' &&
@@ -345,14 +330,12 @@ function getCodeAnalyzer(params: {
   dev: boolean
   compiler: webpack.Compiler
   compilation: webpack.Compilation
-  allowMiddlewareResponseBody: boolean
 }) {
   return (parser: webpack.javascript.JavascriptParser) => {
     const {
       dev,
       compiler: { webpack: wp },
       compilation,
-      allowMiddlewareResponseBody,
     } = params
     const { hooks } = parser
 
@@ -488,32 +471,6 @@ function getCodeAnalyzer(params: {
       }
     }
 
-    /**
-     * A handler for calls to `new Response()` so we can fail if user is setting the response's body.
-     */
-    const handleNewResponseExpression = (node: any) => {
-      const firstParameter = node?.arguments?.[0]
-      if (
-        isInMiddlewareFile(parser) &&
-        firstParameter &&
-        !isNullLiteral(firstParameter) &&
-        !isUndefinedIdentifier(firstParameter)
-      ) {
-        const error = buildWebpackError({
-          message: `Middleware is returning a response body (line: ${node.loc.start.line}), which is not supported.
-Learn more: https://nextjs.org/docs/messages/returning-response-body-in-middleware`,
-          compilation,
-          parser,
-          ...node,
-        })
-        if (dev) {
-          compilation.warnings.push(error)
-        } else {
-          compilation.errors.push(error)
-        }
-      }
-    }
-
     /**
      * Handler to store original source location of static and dynamic imports into module's buildInfo.
      */
@@ -568,10 +525,6 @@ Learn More: https://nextjs.org/docs/messages/node-module-in-edge-runtime`,
         .tap(NAME, handleWrapWasmInstantiateExpression)
     }
 
-    if (!allowMiddlewareResponseBody) {
-      hooks.new.for('Response').tap(NAME, handleNewResponseExpression)
-      hooks.new.for('NextResponse').tap(NAME, handleNewResponseExpression)
-    }
     hooks.callMemberChain.for('process').tap(NAME, handleCallMemberChain)
     hooks.expressionMemberChain.for('process').tap(NAME, handleCallMemberChain)
     hooks.importCall.tap(NAME, handleImport)
@@ -835,23 +788,19 @@ export default class MiddlewarePlugin {
   private readonly dev: boolean
   private readonly sriEnabled: boolean
   private readonly hasFontLoaders: boolean
-  private readonly allowMiddlewareResponseBody: boolean
 
   constructor({
     dev,
     sriEnabled,
     hasFontLoaders,
-    allowMiddlewareResponseBody,
   }: {
     dev: boolean
     sriEnabled: boolean
     hasFontLoaders: boolean
-    allowMiddlewareResponseBody: boolean
   }) {
     this.dev = dev
     this.sriEnabled = sriEnabled
     this.hasFontLoaders = hasFontLoaders
-    this.allowMiddlewareResponseBody = allowMiddlewareResponseBody
   }
 
   public apply(compiler: webpack.Compiler) {
@@ -864,7 +813,6 @@ export default class MiddlewarePlugin {
         dev: this.dev,
         compiler,
         compilation,
-        allowMiddlewareResponseBody: this.allowMiddlewareResponseBody,
       })
       hooks.parser.for('javascript/auto').tap(NAME, codeAnalyzer)
       hooks.parser.for('javascript/dynamic').tap(NAME, codeAnalyzer)

diff --git a/packages/next/build/webpack/plugins/telemetry-plugin.ts b/packages/next/build/webpack/plugins/telemetry-plugin.ts
@@ -38,7 +38,6 @@ export type Feature =
   | `swc/target/${SWC_TARGET_TRIPLE}`
   | 'turbotrace'
   | 'transpilePackages'
-  | 'allowMiddlewareResponseBody'
   | 'skipMiddlewareUrlNormalize'
   | 'skipTrailingSlashRedirect'
 
@@ -101,7 +100,6 @@ const BUILD_FEATURES: Array<Feature> = [
   'swc/target/aarch64-pc-windows-msvc',
   'turbotrace',
   'transpilePackages',
-  'allowMiddlewareResponseBody',
   'skipMiddlewareUrlNormalize',
   'skipTrailingSlashRedirect',
 ]

diff --git a/packages/next/server/config-schema.ts b/packages/next/server/config-schema.ts
@@ -7,9 +7,6 @@ const configSchema = {
   type: 'object',
   additionalProperties: false,
   properties: {
-    allowMiddlewareResponseBody: {
-      type: 'boolean',
-    },
     amp: {
       additionalProperties: false,
       properties: {

diff --git a/packages/next/server/config-shared.ts b/packages/next/server/config-shared.ts
@@ -504,8 +504,6 @@ export interface NextConfig extends Record<string, any> {
   // A list of packages that should always be transpiled and bundled in the server
   transpilePackages?: string[]
 
-  allowMiddlewareResponseBody?: boolean
-
   skipMiddlewareUrlNormalize?: boolean
 
   skipTrailingSlashRedirect?: boolean

diff --git a/packages/next/server/config.ts b/packages/next/server/config.ts
@@ -615,18 +615,6 @@ function assignDefaults(dir: string, userConfig: { [key: string]: any }) {
     result.transpilePackages = (result.experimental as any).transpilePackages
   }
 
-  if (
-    result.experimental &&
-    'allowMiddlewareResponseBody' in (result.experimental as any)
-  ) {
-    Log.warn(
-      `\`allowMiddlewareResponseBody\` has been moved out of \`experimental\`. Please update your ${configFileName} file accordingly.`
-    )
-    result.allowMiddlewareResponseBody = (
-      result.experimental as any
-    ).allowMiddlewareResponseBody
-  }
-
   if (
     result.experimental &&
     'skipMiddlewareUrlNormalize' in (result.experimental as any)

diff --git a/packages/next/server/web/adapter.ts b/packages/next/server/web/adapter.ts
@@ -198,32 +198,6 @@ export async function adapter(params: {
   }
 }
 
-export function blockUnallowedResponse(
-  promise: Promise<FetchEventResult>
-): Promise<FetchEventResult> {
-  if (process.env.__NEXT_ALLOW_MIDDLEWARE_RESPONSE_BODY) {
-    return promise
-  }
-
-  return promise.then((result) => {
-    if (result.response?.body) {
-      console.error(
-        new Error(
-          `A middleware can not alter response's body. Learn more: https://nextjs.org/docs/messages/returning-response-body-in-middleware`
-        )
-      )
-      return {
-        ...result,
-        response: new Response('Internal Server Error', {
-          status: 500,
-          statusText: 'Internal Server Error',
-        }),
-      }
-    }
-    return result
-  })
-}
-
 function getUnsupportedModuleErrorMessage(module: string) {
   // warning: if you change these messages, you must adjust how react-dev-overlay's middleware detects modules not found
   return `The edge runtime does not support Node.js '${module}' module.

diff --git a/packages/next/telemetry/events/build.ts b/packages/next/telemetry/events/build.ts
@@ -167,7 +167,6 @@ export type EventBuildFeatureUsage = {
     | 'build-lint'
     | 'vercelImageGeneration'
     | 'transpilePackages'
-    | 'allowMiddlewareResponseBody'
     | 'skipMiddlewareUrlNormalize'
     | 'skipTrailingSlashRedirect'
   invocationCount: number

diff --git a/test/development/middleware-warnings/index.test.ts b/test/development/middleware-warnings/index.test.ts
@@ -61,9 +61,9 @@ describe('middlewares', () => {
               return new Response(await fetch('https://example.vercel.sh'));
             }`,
     },
-  ])('warns when $title', async ({ code }) => {
+  ])('does not warn when $title', async ({ code }) => {
     ;({ cleanup } = await sandbox(next, new Map([[middlewarePath, code]])))
-    expect(next.cliOutput).toMatch(middlewareWarning)
+    expect(next.cliOutput).not.toMatch(middlewareWarning)
   })
 
   it.each([

diff --git a/test/e2e/app-dir/app-middleware/next.config.js b/test/e2e/app-dir/app-middleware/next.config.js
@@ -1,5 +1,4 @@
 module.exports = {
-  allowMiddlewareResponseBody: true,
   experimental: {
     appDir: true,
   },

diff --git a/test/e2e/middleware-responses/test/index.test.ts b/test/e2e/middleware-responses/test/index.test.ts
@@ -29,25 +29,23 @@ describe('Middleware Responses', () => {
       ])
     })
 
-    it(`${label}should fail when returning a stream`, async () => {
+    it(`${label}should not fail when returning a stream`, async () => {
       const res = await fetchViaHTTP(next.url, `${locale}/stream-a-response`)
-      expect(res.status).toBe(500)
+      expect(res.status).toBe(200)
 
       if (!(global as any).isNextDeploy) {
-        expect(await res.text()).toEqual('Internal Server Error')
-        expect(next.cliOutput).toContain(
+        expect(next.cliOutput).not.toContain(
           `A middleware can not alter response's body. Learn more: https://nextjs.org/docs/messages/returning-response-body-in-middleware`
         )
       }
     })
 
-    it(`${label}should fail when returning a text body`, async () => {
+    it(`${label}should not fail when returning a text body`, async () => {
       const res = await fetchViaHTTP(next.url, `${locale}/send-response`)
-      expect(res.status).toBe(500)
+      expect(res.status).toBe(200)
 
       if (!(global as any).isNextDeploy) {
-        expect(await res.text()).toEqual('Internal Server Error')
-        expect(next.cliOutput).toContain(
+        expect(next.cliOutput).not.toContain(
           `A middleware can not alter response's body. Learn more: https://nextjs.org/docs/messages/returning-response-body-in-middleware`
         )
       }

diff --git a/test/e2e/skip-trailing-slash-redirect/app/next.config.js b/test/e2e/skip-trailing-slash-redirect/app/next.config.js
@@ -1,6 +1,5 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
-  allowMiddlewareResponseBody: true,
   skipMiddlewareUrlNormalize: true,
   skipTrailingSlashRedirect: true,
   async redirects() {

diff --git a/test/integration/middleware-build-errors/test/index.test.js b/test/integration/middleware-build-errors/test/index.test.js
@@ -53,13 +53,13 @@ describe('Middleware validation during build', () => {
   ])('given a middleware $title', ({ code }) => {
     beforeAll(() => writeFile(middlewareFile, code))
 
-    it('throws an error', async () => {
+    it('does not throw an error', async () => {
       const { stderr, code } = await nextBuild(appDir, [], {
         stderr: true,
         stdout: true,
       })
-      expect(stderr).toMatch(middlewareError)
-      expect(code).toBe(1)
+      expect(stderr).not.toMatch(middlewareError)
+      expect(code).toBe(0)
     })
   })
 

diff --git a/test/integration/telemetry/next.config.middleware-options b/test/integration/telemetry/next.config.middleware-options
@@ -1,5 +1,4 @@
 module.exports = {
-  allowMiddlewareResponseBody: true,
   skipMiddlewareUrlNormalize: true,
   skipTrailingSlashRedirect: true,
 }
diff --git a/test/integration/telemetry/test/index.test.js b/test/integration/telemetry/test/index.test.js
@@ -1137,10 +1137,6 @@ describe('Telemetry CLI', () => {
       stderr,
       'NEXT_BUILD_FEATURE_USAGE'
     )
-    expect(featureUsageEvents).toContainEqual({
-      featureName: 'allowMiddlewareResponseBody',
-      invocationCount: 1,
-    })
     expect(featureUsageEvents).toContainEqual({
       featureName: 'skipMiddlewareUrlNormalize',
       invocationCount: 1,