CDN：把內容搬到使用者旁邊

# -s 安靜、-o 丟掉 body、-D - 印標頭；連打兩次比較第二次是否命中
curl -s -o /dev/null -D - https://www.example.com/ | grep -iE "^(age|cache-control|cdn-cache-control|cache-status|cf-cache-status|x-cache|server-timing|vary):"

# 量測各階段時間（DNS、連線、TLS、TTFB、總計）
curl -s -o /dev/null -w "dns %{time_namelookup}s  tcp %{time_connect}s  tls %{time_appconnect}s  ttfb %{time_starttransfer}s  total %{time_total}s  proto %{http_version}\n" https://www.example.com/

# 假裝從另一個地區：多數 CDN 可用特定標頭或 --resolve 指到特定 PoP 的 IP
curl -s -o /dev/null -D - --resolve www.example.com:443:203.0.113.10 https://www.example.com/

const hits = { HIT: 0, MISS: 0, other: 0 };
for (const e of performance.getEntriesByType('resource')) {
  const st = e.serverTiming?.find((s) => s.name === 'cdn-cache');
  if (!st) continue;
  const status = st.description?.toUpperCase();
  hits[status in hits ? status : 'other']++;
}
console.table(hits);

// 也看看走的是什麼協定：h3 表示 QUIC
console.table(
  performance.getEntriesByType('resource').map((e) => ({ host: new URL(e.name).host, proto: e.nextHopProtocol }))
);

<img
  src="https://img.example.com/cdn-cgi/image/width=800,quality=75,format=auto/hero.jpg"
  srcset="
    https://img.example.com/cdn-cgi/image/width=480,quality=75,format=auto/hero.jpg 480w,
    https://img.example.com/cdn-cgi/image/width=800,quality=75,format=auto/hero.jpg 800w,
    https://img.example.com/cdn-cgi/image/width=1200,quality=75,format=auto/hero.jpg 1200w"
  sizes="(max-width: 600px) 100vw, 800px"
  width="800" height="450" alt="..." fetchpriority="high">

export default {
  async fetch(request, env, ctx) {
    const cookie = request.headers.get('Cookie') || '';
    const loggedIn = /session=/.test(cookie);
    if (loggedIn || request.method !== 'GET') {
      return fetch(request);                  // 登入者：直接回源，不進快取
    }
    const cache = caches.default;
    const cacheKey = new Request(new URL(request.url).toString(), request); // 去掉 cookie 影響
    let response = await cache.match(cacheKey);
    if (!response) {
      response = await fetch(request, { cf: { cacheTtl: 600, cacheEverything: true } });
      response = new Response(response.body, response);
      response.headers.set('Cache-Control', 'public, max-age=0, s-maxage=600');
      ctx.waitUntil(cache.put(cacheKey, response.clone()));
    }
    return response;
  },
};