Vercel Routing Middleware 実装ガイド：認証ゲート・パーソナライズ・A/B・リダイレクトをキャッシュ前で

// middleware.ts（プロジェクトルート）
export default function middleware(request: Request) {
  const url = new URL(request.url);

  // 旧パスをリダイレクト
  if (url.pathname === "/old-page") {
    return new Response(null, {
      status: 302,
      headers: { Location: "/new-page" },
    });
  }

  // 次のハンドラへ続行
  return new Response("Hello from your Middleware!");
}

// middleware.ts — Node.js ランタイムに切り替え
export const config = {
  runtime: "nodejs", // 既定は 'edge'
};

export default function middleware(request: Request) {
  return new Response("Hello from Node.js Middleware!");
}

// middleware.ts
const PROTECTED = ["/dashboard", "/settings", "/billing"];

export default function middleware(request: Request) {
  const url = new URL(request.url);
  const needsAuth = PROTECTED.some((p) => url.pathname.startsWith(p));
  if (!needsAuth) return; // 続行

  const session = request.headers.get("cookie")?.includes("session=");
  if (!session) {
    const login = new URL("/login", request.url);
    login.searchParams.set("next", url.pathname); // 戻り先を保持
    return Response.redirect(login, 307);
  }
}

// middleware.ts — 国に応じてロケールへ rewrite（キャッシュは活きる）
export default function middleware(request: Request) {
  const url = new URL(request.url);
  if (url.pathname !== "/") return;

  const country = request.headers.get("x-vercel-ip-country") ?? "US";
  const locale = country === "JP" ? "ja" : "en";

  // rewrite（URLは変えずに内部的に別ページを返す）
  const rewritten = new URL(`/${locale}`, request.url);
  return new Response(null, {
    status: 200,
    headers: { "x-middleware-rewrite": rewritten.toString() },
  });
}

// middleware.ts
export default function middleware(request: Request) {
  const url = new URL(request.url);
  if (url.pathname !== "/") return;

  const cookie = request.headers.get("cookie") ?? "";
  let bucket = cookie.match(/ab=(a|b)/)?.[1];

  const res = new Response(null, { status: 200 });
  if (!bucket) {
    bucket = Math.random() < 0.5 ? "a" : "b";
    res.headers.append("set-cookie", `ab=${bucket}; Path=/; Max-Age=2592000`);
  }
  res.headers.set(
    "x-middleware-rewrite",
    new URL(bucket === "b" ? "/home-variant" : "/", request.url).toString(),
  );
  return res;
}

// middleware.ts — Edge Config で「再デプロイなしの」制御
import { get } from "@vercel/edge-config";

export default async function middleware(request: Request) {
  // メンテモード（コードを触らず即ON/OFF）
  if (await get<boolean>("maintenance_mode")) {
    return Response.redirect(new URL("/maintenance", request.url), 307);
  }

  // 悪性IPブロック（アップストリームを呼ばずに弾く）
  const ip = request.headers.get("x-forwarded-for")?.split(",")[0];
  const blocked = (await get<string[]>("blocked_ips")) ?? [];
  if (ip && blocked.includes(ip)) {
    return new Response("Forbidden", { status: 403 });
  }
}