Max Age Without S Maxage

1import { lineOf } from '../util.mjs';
2
3export const metadata = {
4  id: 'max-age-without-s-maxage',
5  title: 'Cache-Control: max-age without s-maxage',
6  severity: 'medium',
7  billingDimension: 'edge-requests',
8  trafficIndependent: false,
9  description:
10    'max-age caches in the browser; s-maxage caches at the CDN. Without s-maxage, every uncached visitor request invokes the function. Adding s-maxage often cuts function invocations by 80%+ on read-heavy routes.',
11  fix:
12    'Add s-maxage to the Cache-Control header. Example: Cache-Control: public, max-age=60, s-maxage=600, stale-while-revalidate=86400. Pair with explicit cache-bust strategy if content can change.',
13  citations: [
14    'https://vercel.com/docs/caching/cdn-cache',
15    'https://vercel.com/docs/caching/cache-control-headers',
16  ],
17  excludeGlobs: ['node_modules/**', '.next/**', 'dist/**', '__tests__/**', '*.config.*'],
18  includeGlobs: ['**/*.{ts,tsx,js,jsx,mjs}'],
19};
20
21const RE = /Cache-Control[^"'`]*?max-age\s*=\s*\d+/gi;
22
23export function scan({ files }) {
24  const out = [];
25  for (const { path, content } of files) {
26    if (/\.test\.|\.spec\./.test(path)) continue;
27    let m;
28    RE.lastIndex = 0;
29    while ((m = RE.exec(content)) !== null) {
30      const hit = m[0];
31      if (/s-maxage/i.test(hit) || /CDN-Cache-Control/i.test(content.slice(Math.max(0, m.index - 100), m.index + hit.length + 100))) continue;
32      out.push({
33        pattern: metadata.id,
34        file: path,
35        line: lineOf(content, m.index),
36        evidence: hit.slice(0, 160),
37        trafficIndependent: metadata.trafficIndependent,
38      });
39    }
40  }
41  return out;
42}