Next.js 中 middleware 中间件使用方式

project/
 ├── app/
 ├── middleware.ts   👈 全局 Middleware
 └── package.json

import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";

export function middleware(request: NextRequest) {
  // 打印请求路径
  console.log("请求路径:", request.nextUrl.pathname);

  // 例子：未登录就重定向到 /auth/signin
  const isLoggedIn = request.cookies.get("next-auth.session-token");
  console.log("是否登录:", isLoggedIn);

  if (!isLoggedIn && request.nextUrl.pathname.startsWith("/dashboard")) {
    return NextResponse.redirect(new URL("/auth/signin", request.url));
  }

  // 默认放行
  return NextResponse.next();
}

// 匹配规则：只在 /dashboard 下生效
export const config = {
  matcher: ["/dashboard/:path*"]
};

export function middleware(request: NextRequest) {
  const { pathname } = request.nextUrl;

  // 如果路径没有语言前缀，重写到默认语言
  if (!pathname.startsWith("/en") && !pathname.startsWith("/zh")) {
    const url = request.nextUrl.clone();
    url.pathname = `/en${pathname}`;
    return NextResponse.rewrite(url);
  }

  return NextResponse.next();
}

export function middleware(request: NextRequest) {
  const response = NextResponse.next();

  // 简单随机分流
  if (Math.random() > 0.5) {
    return NextResponse.rewrite(new URL("/experiment-a", request.url));
  }
  return NextResponse.rewrite(new URL("/experiment-b", request.url));
}

export function middleware(request: NextRequest) {
  const referer = request.headers.get("referer");
  if (referer && !referer.includes("yourdomain.com")) {
    return new NextResponse("禁止访问", { status: 403 });
  }
  return NextResponse.next();
}