open-standards/aac/aac-rs/crates/aac-web/static/sw.js

// Service worker for the AAC reference app — offline-first.
//
// AAC must never fail because of network. prerender-static.sh fills in
// VERSION (a hash of everything below), PRECACHE_URLS (the app shell and
// every file it loads, including wasm-bindgen snippets, the symbol sprites
// the first frame draws, and the symbols' LICENSES.md), VENDOR_DIRS (the vendored library directories this
// build ships) and SYMBOL_FILES (every symbol sprite this build ships). A new version installs
// completely before it replaces the old one, so the shell served is always the
// one that matches its files. Content-hashed files already held from the last
// version are copied across instead of downloaded again. Only successful,
// same-origin GET responses are ever cached.
//
// The app is served cross-origin isolated (COOP + COEP), which threaded WASM
// needs for SharedArrayBuffer. Every file it loads is same-origin, including
// the eye-tracking library, which the build vendors under vendor/.

const VERSION = '__VERSION__';
const PRECACHE = 'aac-precache-' + VERSION;
const RUNTIME = 'aac-runtime';
const RUNTIME_MAX = 150;
// Vendored libraries (eye tracking, ~16 MB) are cached on first use rather
// than precached, so installing the app stays light. They live in their own
// cache so the runtime cache's trimming never evicts part of one. Each
// directory's name changes whenever its bytes do (third_party/mediapipe/
// vendor.sh), so the cache holds only this build's directories.
const VENDOR = 'aac-vendor';
const VENDOR_PATH = new URL('vendor/', self.registration.scope).pathname;
const VENDOR_DIRS = __VENDOR_DIRS__.map((dir) => VENDOR_PATH + dir);
const IN_VENDOR_DIRS = (path) => VENDOR_DIRS.some((dir) => path.startsWith(dir));
// Voice and model packs (src/bindings/model_store.js) are published under
// models/ and fetched with cache: 'no-store'. The worker leaves both to the
// network: the store verifies a pack and keeps it in its own cache, and a
// second, unverified copy here would double its size and could be served back
// in place of a corrected download.
const MODELS_PATH = new URL('models/', self.registration.scope).pathname;
const PRECACHE_URLS = __PRECACHE_URLS__;
// Symbol sprites (symbols/<set>.<hash>.svg). Those the prerendered board draws
// are precached, so symbols show offline from the first visit; another set is
// cached the first time it is drawn. They live in their own cache so the
// runtime cache's trimming never evicts one; it keeps this build's sprites and,
// until the next update, the previous build's (a tab still open on it may yet
// draw one). symbols/LICENSES.md is precached, and opening it (a navigation)
// gets the file, never the app shell.
const SYMBOLS = 'aac-symbols';
const SYMBOLS_PATH = new URL('symbols/', self.registration.scope).pathname;
const SYMBOL_URLS = __SYMBOL_FILES__.map((file) => SYMBOLS_PATH + file);
// A name like aac-web.0123456789ab.wasm never changes content.
const IMMUTABLE = (path) => /\.[0-9a-f]{12}\.[a-z0-9]+$/.test(path);

// Installing never hangs, and never gives up on a network that is only slow.
// Every file of this version is fetched and cached, or the install fails:
// this worker is discarded, and the app registers it again
// (src/bindings/sw_keeper.js).
// - A file whose answer has begun and then stops coming (no bytes for
//   STALL_MS) is given up. A request still waiting for its answer is not timed
//   on its own: the browser keeps only a few of a worker's requests on the
//   wire, and the rest wait their turn, however long the others take.
// - The install is given up when nothing at all has moved for STALL_MS (no
//   file's bytes, no cache answering), and every request still open is
//   cancelled.
// - Each file is fetched to its end even when another has failed, so the next
//   attempt finds every finished content-hashed file in the cache and copies
//   it instead of downloading it again.
// - Two registrations of this worker (the site's, and the app's own when
//   WebKit lost the site's: sw_keeper.js) never both download a
//   content-hashed file: one fetches it while the other waits, then copies it.
const STALL_MS = 30000;
// How the install is going, for the app, which asks (a message
// { type: 'aac-sw-progress' } with a port to answer on). WebKit can leave a
// worker "installing" without ever giving it its install event (the page that
// registered it went away while it started; see sw_keeper.js), and the app
// can only tell that worker from a slow one by asking it.
const STARTED = Date.now();
const install = { started: 0, done: 0, moved: STARTED, failed: '' };
const moved = () => { install.moved = Date.now(); };

self.addEventListener('message', (event) => {
  const port = event.ports && event.ports[0];
  if (!port || !event.data || event.data.type !== 'aac-sw-progress') return;
  const now = Date.now();
  port.postMessage({
    version: VERSION, sinceStart: now - STARTED, installing: install.started > 0,
    done: install.done, total: PRECACHE_URLS.length, sinceMoved: now - install.moved, failed: install.failed,
  });
});

// A request from this version's precache first, then from any other cache
// (an older copy of a file whose name does not change, in the runtime cache,
// must not win over this version's).
async function cached(request, options) {
  return (await caches.match(request, { ...options, cacheName: PRECACHE })) || caches.match(request, options);
}

// When this version's precache was begun, kept in it: activate removes only
// precaches begun before its own, so it never takes the files of a newer
// version that another registration of this worker is installing or using.
const BEGUN = new URL('.aac-precache-begun', self.registration.scope).pathname;
async function begun(cache) {
  const r = await cache.match(BEGUN);
  return r ? Number(await r.text()) || 0 : 0;
}

async function download(cache, url, all) {
  if (all.signal.aborted) throw all.signal.reason;
  const own = new AbortController();
  const stop = () => own.abort(all.signal.reason);
  all.signal.addEventListener('abort', stop, { once: true });
  let timer = 0;
  const alive = () => {
    moved();
    clearTimeout(timer);
    timer = setTimeout(() => own.abort(new Error('precache ' + url + ': nothing arrived for ' + STALL_MS / 1000 + ' s')), STALL_MS);
  };
  let counting = null;
  try {
    const res = await fetch(new Request(url, { cache: 'reload', signal: own.signal }));
    if (!res.ok) throw new Error('precache ' + url + ' ' + res.status);
    // Timed on its own from its first answer on.
    alive();
    // Its bytes counted as they arrive (from a copy: what is cached is the
    // response itself), so a slow file that keeps coming is never cut off.
    counting = res.body && res.clone().body.getReader();
    if (counting) (async () => { while (!(await counting.read()).done) alive(); })().catch(() => {});
    await cache.put(url, res);
  } finally {
    clearTimeout(timer);
    all.signal.removeEventListener('abort', stop);
    if (counting) counting.cancel().catch(() => {});
  }
}

async function precache(cache, url, all) {
  if (!IMMUTABLE(url)) return download(cache, url, all);
  // Any copy of a content-hashed file is this file. One already in this
  // version's precache (another registration of this worker, or an earlier
  // attempt, put it there: a file is only there once it is whole) is left as
  // it is.
  const copy = async () => {
    if (await cache.match(url, { ignoreVary: true })) {
      moved();
      return true;
    }
    const held = await caches.match(url, { ignoreVary: true });
    moved();
    if (!held) return false;
    await cache.put(url, held);
    return true;
  };
  if (await copy()) return;
  const locks = self.navigator && self.navigator.locks;
  if (!locks) return download(cache, url, all);
  // While another registration's install holds the file, this one is waiting,
  // not stalled (that install bounds itself, and its lock goes with it).
  const waiting = setInterval(moved, 5000);
  try {
    await locks.request('aac-precache ' + url, async () => {
      clearInterval(waiting);
      if (!(await copy())) await download(cache, url, all);
    });
  } finally {
    clearInterval(waiting);
  }
}

self.addEventListener('install', (event) => {
  install.started = Date.now();
  moved();
  const all = new AbortController();
  let watchdog = 0;
  const stalled = new Promise((resolve, reject) => {
    watchdog = setInterval(() => {
      if (Date.now() - install.moved <= STALL_MS) return;
      const e = new Error('install: nothing moved for ' + STALL_MS / 1000 + ' s');
      all.abort(e);
      reject(e);
    }, 1000);
  });
  const work = (async () => {
    const cache = await caches.open(PRECACHE);
    if (!(await begun(cache))) await cache.put(BEGUN, new Response(String(Date.now())));
    moved();
    const results = await Promise.allSettled(PRECACHE_URLS.map(async (url) => {
      await precache(cache, url, all);
      install.done += 1;
      moved();
    }));
    const failed = results.find((r) => r.status === 'rejected');
    if (failed) throw failed.reason;
    await self.skipWaiting();
  })();
  event.waitUntil(Promise.race([work, stalled])
    .catch((e) => { install.failed = String((e && e.message) || e); throw e; })
    .finally(() => clearInterval(watchdog)));
});

self.addEventListener('activate', (event) => {
  event.waitUntil((async () => {
    const keep = new Set([PRECACHE, RUNTIME, VENDOR, SYMBOLS]);
    const mine = await begun(await caches.open(PRECACHE));
    // A precache begun after this one is a newer version's, which another
    // registration of this worker is installing or using: it stays. An older
    // one goes, even while another registration's worker still runs that
    // version: that worker then answers from the copies that remain (cached()
    // looks in every cache) until it updates, as it does at the next visit.
    for (const key of await caches.keys()) {
      if (key.startsWith('aac-precache-') && key !== PRECACHE && mine && (await begun(await caches.open(key))) > mine) keep.add(key);
    }
    // A tab still open on the previous version keeps running its shell, and
    // may yet draw a sprite it has not drawn (another set, another board):
    // carry that version's precached sprites over until the next update.
    const symbols = await caches.open(SYMBOLS);
    const carried = new Set();
    for (const key of await caches.keys()) {
      if (!key.startsWith('aac-precache-') || keep.has(key)) continue;
      const old = await caches.open(key);
      for (const req of await old.keys()) {
        const path = new URL(req.url).pathname;
        if (path.startsWith(SYMBOLS_PATH) && path.endsWith('.svg') && !SYMBOL_URLS.includes(path)) {
          await symbols.put(path, await old.match(req));
          carried.add(path);
        }
      }
    }
    // Also removes the cache of the first release ('aac-v1'). Downloaded voice
    // and model packs ('aac-models-*') belong to the person, not to a release:
    // they were fetched on request and must survive every update.
    for (const key of await caches.keys()) {
      if (key.startsWith('aac-') && !key.startsWith('aac-models-') && !keep.has(key)) await caches.delete(key);
    }
    // Vendored files from earlier builds (their directory has another name).
    const vendor = await caches.open(VENDOR);
    for (const req of await vendor.keys()) {
      if (!IN_VENDOR_DIRS(new URL(req.url).pathname)) await vendor.delete(req);
    }
    // Sprites from older builds (their name has another hash).
    for (const req of await symbols.keys()) {
      const path = new URL(req.url).pathname;
      if (!SYMBOL_URLS.includes(path) && !carried.has(path)) await symbols.delete(req);
    }
    await self.clients.claim();
  })());
});

// Cross-origin isolation for the app shell. The server sends these headers,
// but a shell cached before it did would keep the app un-isolated until the
// app's content next changed, so the worker states them on every shell it
// serves. Redirects and errors pass through untouched.
function isolated(res) {
  if (res.type === 'opaqueredirect' || !res.ok) return res;
  const headers = new Headers(res.headers);
  headers.set('Cross-Origin-Opener-Policy', 'same-origin');
  headers.set('Cross-Origin-Embedder-Policy', 'require-corp');
  return new Response(res.body, { status: res.status, statusText: res.statusText, headers });
}

async function trim(cache) {
  const keys = await cache.keys();
  for (let i = 0; i < keys.length - RUNTIME_MAX; i++) await cache.delete(keys[i]);
}

self.addEventListener('fetch', (event) => {
  const req = event.request;
  if (req.method !== 'GET') return;
  const url = new URL(req.url);
  // Other origins, any API and model packs are left to the network.
  if (url.origin !== self.location.origin || url.pathname.startsWith('/api/')) return;
  if (req.cache === 'no-store' || url.pathname.startsWith(MODELS_PATH)) return;

  // Symbols: sprites (drawn by <use>) and LICENSES.md (opened from Settings,
  // a navigation, so this comes before the shell below). A current sprite not
  // yet held is cached the first time it is drawn.
  if (url.pathname.startsWith(SYMBOLS_PATH)) {
    event.respondWith((async () => {
      const hit = await cached(url.pathname);
      if (hit) return hit;
      const res = await fetch(req);
      const html = (res.headers.get('Content-Type') || '').startsWith('text/html');
      if (res.ok && res.type === 'basic' && !html && SYMBOL_URLS.includes(url.pathname)) {
        const copy = res.clone();
        event.waitUntil(caches.open(SYMBOLS).then((cache) => cache.put(url.pathname, copy)));
      }
      return res;
    })());
    return;
  }

  // The app is one screen: every other navigation gets the precached shell.
  if (req.mode === 'navigate') {
    event.respondWith(cached('/').then((hit) => hit || fetch(req)).then(isolated));
    return;
  }

  if (url.pathname.startsWith(VENDOR_PATH)) {
    event.respondWith((async () => {
      // A library file is the same whatever asked for it (see below: Vary).
      const hit = await caches.match(req, { ignoreVary: true });
      if (hit) return hit;
      const res = await fetch(req);
      // Never an HTML page: a server that answers unknown paths with its
      // index would otherwise leave that page here in place of a library file.
      const html = (res.headers.get('Content-Type') || '').startsWith('text/html');
      if (res.ok && res.type === 'basic' && !html && IN_VENDOR_DIRS(url.pathname)) {
        const copy = res.clone();
        event.waitUntil(caches.open(VENDOR).then((cache) => cache.put(req, copy)));
      }
      return res;
    })());
    return;
  }

  event.respondWith((async () => {
    // Content-hashed and precached files are the same whatever asked for them:
    // a server's Vary (Vary: Origin; a module import carries an Origin header,
    // the precache's own request does not) must not make them miss offline.
    const fixed = IMMUTABLE(url.pathname) || PRECACHE_URLS.includes(url.pathname);
    const hit = fixed ? await cached(req, { ignoreVary: true }) : await caches.match(req);
    if (hit) return hit;
    const res = await fetch(req);
    if (res.ok && res.type === 'basic') {
      const cache = await caches.open(RUNTIME);
      cache.put(req, res.clone()).then(() => trim(cache));
    }
    return res;
  })());
});