DecodeError from invalid URI causes 500 with middleware (vs 400 without)

packages/next/server/dev/next-dev-server.ts

@@ -632,6 +632,9 @@ export default class DevServer extends Server {
       )
       return result
     } catch (error) {
+      if (error instanceof DecodeError) {
+        throw error
+      }
       this.logErrorWithOriginalStack(error, undefined, 'edge-server')
 
       const preflight =

packages/next/server/next-server.ts

@@ -2,7 +2,7 @@ import './node-polyfill-fetch'
 import './node-polyfill-web-streams'
 
 import type { Route } from './router'
-import type { CacheFs } from '../shared/lib/utils'
+import { CacheFs, DecodeError, execOnce } from '../shared/lib/utils'
 import type { MiddlewareManifest } from '../build/webpack/plugins/middleware-plugin'
 import type RenderResult from './render-result'
 import type { FetchEventResult } from './web/types'
@@ -18,8 +18,6 @@ import type { Params } from '../shared/lib/router/utils/route-matcher'
 import fs from 'fs'
 import { join, relative, resolve, sep } from 'path'
 import { IncomingMessage, ServerResponse } from 'http'
-
-import { execOnce } from '../shared/lib/utils'
 import { addRequestMeta, getRequestMeta } from './request-meta'
 
 import {
@@ -1252,6 +1250,12 @@ export default class NextNodeServer extends BaseServer {
             return { finished: true }
           }
 
+          if (err instanceof DecodeError) {
+            res.statusCode = 400
+            this.renderError(err, req, res, parsed.pathname || '')
+            return { finished: true }
+          }
+
           const error = getProperError(err)
           console.error(error)
           res.statusCode = 500

test/integration/middleware-general/test/index.test.js

@@ -27,6 +27,7 @@ describe('Middleware Runtime', () => {
   describe('dev mode', () => {
     afterAll(() => killApp(context.app))
     beforeAll(async () => {
+      context.dev = true
       context.appPort = await findPort()
       context.app = await launchApp(context.appDir, context.appPort, {
         env: {
@@ -87,6 +88,7 @@ describe('Middleware Runtime', () => {
         stderr: build.stderr,
         stdout: build.stdout,
       }
+      context.dev = false
 
       context.appPort = await findPort()
       context.app = await nextStart(context.appDir, context.appPort, {
@@ -133,6 +135,15 @@ describe('Middleware Runtime', () => {
 })
 
 function tests(context, locale = '') {
+  it('should respond with 400 on decode failure', async () => {
+    const res = await fetchViaHTTP(context.appPort, `${locale}/%2`)
+    expect(res.status).toBe(400)
+
+    if (!context.dev) {
+      expect(await res.text()).toContain('Bad Request')
+    }
+  })
+
   it('should set fetch user agent correctly', async () => {
     const res = await fetchViaHTTP(
       context.appPort,