As we work on improving Middleware for General Availability (GA), we've made some changes to the Middleware APIs (and how you define Middleware in your application) based on your feedback.
This upgrade guide will help you understand the changes and how to migrate your existing Middleware to the new API. The guide is for Next.js developers who:
- Currently use the beta Next.js Middleware features
- Choose to upgrade to the next stable version of Next.js (
v12.2)
You can start upgrading your Middleware usage today with the latest canary release (npm i next@canary).
If you have ESLint configured, you will need to run npm i eslint-config-next@canary --save-dev to upgrade your ESLint configuration to ensure the same version is being used as the Next.js version. You might also need to restart VSCode for the changes to take effect.
If you're using Next.js on Vercel, your existing deploys using Middleware will continue to work, and you can continue to deploy your site using Middleware. When you upgrade your site to the next stable version of Next.js (v12.2), you will need to follow this upgrade guide to update your Middleware.
- No Nested Middleware
- No Response Body
- Cookies API Revamped
- New User-Agent Helper
- No More Page Match Data
- Executing Middleware on Internal Next.js Requests
- Define a single Middleware file next to your
pagesfolder - No need to prefix the file with an underscore
- A custom matcher can be used to define matching routes using an exported config object
Previously, you could create a _middleware.ts file under the pages directory at any level. Middleware execution was based on the file path where it was created. Beta customers found this route matching confusing. For example:
- Middleware in
pages/dashboard/_middleware.ts - Middleware in
pages/dashboard/users/_middleware.ts - A request to
/dashboard/users/*would match both.
Based on customer feedback, we have replaced this API with a single root Middleware.
You should declare one single Middleware file in your application, which should be located next to the pages directory and named without an _ prefix. Your Middleware file can still have either a .ts or .js extension.
Middleware will be invoked for every route in the app, and a custom matcher can be used to define matching filters. The following is an example for a Middleware that triggers for /about/* and /dashboard/:path*, the custom matcher is defined in an exported config object:
// middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
return NextResponse.rewrite(new URL('/about-2', request.url))
}
// Supports both a single string value or an array of matchers
export const config = {
matcher: ['/about/:path*', '/dashboard/:path*'],
}While the config option is preferred since it doesn't get invoked on every request, you can also use conditional statements to only run the Middleware when it matches specific paths. One advantage of using conditionals is defining explicit ordering for when Middleware executes. The following example shows how you can merge two previously nested Middleware:
// <root>/middleware.js
import type { NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
if (request.nextUrl.pathname.startsWith('/about')) {
// This logic is only applied to /about
}
if (request.nextUrl.pathname.startsWith('/dashboard')) {
// This logic is only applied to /dashboard
}
}- Middleware can no longer respond with a body
- If your Middleware does respond with a body, a runtime error will be thrown
- Migrate to using
rewrite/redirectto pages/APIs handling a response
To help ensure security, we are removing the ability to send response bodies in Middleware. This ensures that Middleware is only used to rewrite, redirect, or modify the incoming request (e.g. setting cookies).
The following patterns will no longer work:
new Response('a text value')
new Response(streamOrBuffer)
new Response(JSON.stringify(obj), { headers: 'application/json' })
NextResponse.json()For cases where Middleware is used to respond (such as authorization), you should migrate to use rewrite/redirect to pages that show an authorization error, login forms, or to an API Route.
// pages/_middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
import { isAuthValid } from './lib/auth'
export function middleware(request: NextRequest) {
// Example function to validate auth
if (isAuthValid(req)) {
return NextResponse.next()
}
return NextResponse.json({ message: 'Auth required' }, { status: 401 })
}// middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
import { isAuthValid } from './lib/auth'
export function middleware(request: NextRequest) {
// Example function to validate auth
if (isAuthValid(req)) {
return NextResponse.next()
}
const loginUrl = new URL('/login', request.url)
loginUrl.searchParams.set('from', request.nextUrl.pathname)
return NextResponse.redirect(loginUrl)
}| Added | Removed |
|---|---|
cookie.set |
cookie |
cookie.delete |
clearCookie |
cookie.getWithOptions |
cookies |
Based on beta feedback, we are changing the Cookies API in NextRequest and NextResponse to align more to a get/set model. The Cookies API extends Map, including methods like entries and values.
NextResponse now has a cookies instance with:
cookie.deletecookie.setcookie.getWithOptions
As well as other extended methods from Map.
// pages/_middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
// create an instance of the class to access the public methods. This uses `next()`,
// you could use `redirect()` or `rewrite()` as well
let response = NextResponse.next()
// get the cookies from the request
let cookieFromRequest = request.cookies['my-cookie']
// set the `cookie`
response.cookie('hello', 'world')
// set the `cookie` with options
const cookieWithOptions = response.cookie('hello', 'world', {
path: '/',
maxAge: 1000 * 60 * 60 * 24 * 7,
httpOnly: true,
sameSite: 'strict',
domain: 'example.com',
})
// clear the `cookie`
response.clearCookie('hello')
return response
}// middleware.ts
export function middleware() {
const response = new NextResponse()
// set a cookie
response.cookies.set('vercel', 'fast')
// set another cookie with options
response.cookies.set('nextjs', 'awesome', { path: '/test' })
// get all the details of a cookie
const { value, options } = response.cookies.getWithOptions('vercel')
console.log(value) // => 'fast'
console.log(options) // => { Path: '/test' }
// deleting a cookie will mark it as expired
response.cookies.delete('vercel')
// clear all cookies means mark all of them as expired
response.cookies.clear()
return response
}- Accessing the user agent is no longer available on the request object
- We've added a new
userAgenthelper to reduce Middleware size by17kb
To help reduce the size of your Middleware, we have extracted the user agent from the request object and created a new helper userAgent.
The helper is imported from next/server and allows you to opt in to using the user agent. The helper gives you access to the same properties that were available from the request object.
- Import the
userAgenthelper fromnext/server - Destructure the properties you need to work with
// pages/_middleware.ts
import { NextRequest, NextResponse } from 'next/server'
export function middleware(request: NextRequest) {
const url = request.nextUrl
const viewport = request.ua.device.type === 'mobile' ? 'mobile' : 'desktop'
url.searchParams.set('viewport', viewport)
return NextResponse.rewrite(url)
}// middleware.ts
import { NextRequest, NextResponse, userAgent } from 'next/server'
export function middleware(request: NextRequest) {
const url = request.nextUrl
const { device } = userAgent(request)
const viewport = device.type === 'mobile' ? 'mobile' : 'desktop'
url.searchParams.set('viewport', viewport)
return NextResponse.rewrite(url)
}- Use
URLPatternto check if a Middleware is being invoked for a certain page match
Currently, Middleware estimates whether you are serving an asset of a Page based on the Next.js routes manifest (internal configuration). This value is surfaced through request.page.
To make page and asset matching more accurate, we are now using the web standard URLPattern API.
Use URLPattern to check if a Middleware is being invoked for a certain page match.
// pages/_middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
export function middleware(request: NextRequest) {
const { params } = event.request.page
const { locale, slug } = params
if (locale && slug) {
const { search, protocol, host } = request.nextUrl
const url = new URL(`${protocol}//${locale}.${host}/${slug}${search}`)
return NextResponse.redirect(url)
}
}// middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
const PATTERNS = [
[
new URLPattern({ pathname: '/:locale/:slug' }),
({ pathname }) => pathname.groups,
],
]
const params = (url) => {
const input = url.split('?')[0]
let result = {}
for (const [pattern, handler] of PATTERNS) {
const patternResult = pattern.exec(input)
if (patternResult !== null && 'pathname' in patternResult) {
result = handler(patternResult)
break
}
}
return result
}
export function middleware(request: NextRequest) {
const { locale, slug } = params(request.url)
if (locale && slug) {
const { search, protocol, host } = request.nextUrl
const url = new URL(`${protocol}//${locale}.${host}/${slug}${search}`)
return NextResponse.redirect(url)
}
}- Middleware will be executed for all requests, including
_next
Prior to Next.js v12.2, Middleware was not executed for _next requests.
For cases where Middleware is used for authorization, you should migrate to use rewrite/redirect to Pages that show an authorization error, login forms, or to an API Route.
See No Reponse Body for an example of how to migrate to use rewrite/redirect.