sw.js

/* sw.js */
self.addEventListener('install', (e) => { self.skipWaiting(); });
self.addEventListener('activate', (e) => { e.waitUntil(self.clients.claim()); });

let currentDiff = null; //{response0, response1}

self.addEventListener('message', (e) => {
  const { type, diff } = e.data || {};
  if (type === 'SET_DIFF' && diff && diff.response0 && diff.response1) {
    currentDiff = diff;
    if (e.ports && e.ports[0]) e.ports[0].postMessage({ type: 'DIFF_SET' });
    else if (e.source?.postMessage) e.source.postMessage({ type: 'DIFF_SET' });
  }
});

function pickStateHeaders(url) {
  if (!currentDiff) return null;
  const u = new URL(url);
  const state = u.searchParams.get('state') === '1' ? 1 : 0;
  return state === 1 ? currentDiff.response1 : currentDiff.response0;
}

self.addEventListener('fetch', (event) => {
  const url = new URL(event.request.url);

  // Intercept same-origin /filetemplates/*
  if (url.origin === self.location.origin && url.pathname.startsWith('/filetemplates/')) {
    event.respondWith((async () => {
      const orig = await fetch(event.request);
      const override = pickStateHeaders(event.request.url);
      const h = new Headers(orig.headers);

      if (override && Array.isArray(override.headers)) {
        for (const { name, value } of override.headers) { try { h.set(name, value); } catch {} }
      }
      //Helpful state marker
      h.set('X-AutoLeak-State', new URL(event.request.url).searchParams.get('state') || '0');

      const body = await orig.blob();
      const status = (override && override.status) ? override.status : orig.status;
      return new Response(body, { status, statusText: orig.statusText || 'OK', headers: h });
    })());
    return;
  }

  event.respondWith(fetch(event.request));
});