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Interactive static assets stop loading after the browser stops the idle service worker, which keeps them only in memory

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
76/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
typescript
Domain
backend

Research direction

Start with packages/runtime-internal/src/interactive/worker.js and bootstrap.js to trace how static assets are registered and fetched; then read the named worker test and its Cache Storage test globals. Implement persistent asset storage across worker restarts, and verify the unit test plus the CDP end-to-end test in testing/src/specs/instrument-completion.spec.ts pass, including after a stopped worker is restarted.

Written by the indexing model from the issue text.

Description

Area: Instruments Bug Difficulty: Medium Priority: Medium

An interactive instrument's static assets stop loading once the browser stops its idle service worker. worker.js keeps the assets only in a module-level Map. Browsers terminate a service worker that has handled no event for about 30 seconds (Chrome and Firefox both use a 30 s idle timeout), even while a page it controls is open, and the next fetch starts a fresh copy of the script with an empty map. bootstrap.js posts the assets only once, before render. So any asset first requested after a pause of more than 30 s with no network activity misses the map and goes to the network, where it does not exist. Typical cases are a stimulus image shown after an instruction screen, or a sound played on a later trial. The participant sees a broken image or hears nothing, partway through a task whose data is then recorded as if the stimulus had been shown.

Where

packages/runtime-internal/src/interactive/worker.js:5-6 and 53-77:

/** @type {Map<string, string>} */
const staticAssets = new Map();
// ...
addEventListener('message', (event) => {
  // ...
  Object.entries(data.staticAssets).forEach(([key, value]) => {
    staticAssets.set(key, value);
  });
  event.ports[0]?.postMessage({ type: 'STATIC_ASSETS_READY' });
});

worker.addEventListener('fetch', (_event) => {
  // ...
  if (staticAssets.has(pathname)) {

packages/runtime-internal/src/interactive/bootstrap.js:49-74 sends STATIC_ASSETS once, at startup, and never again.

Reproduce

  1. Use the playground example "Interactive Instrument with Static Assets", changed so the <img src="smiley.png"> is inserted on a button click instead of being in the initial HTML.
  2. Open it in apps/web in Chrome.
  3. Wait more than 30 s without interacting, or click "stop" for the worker under DevTools > Application > Service workers, which does the same as an idle termination. Then click the button.

Actual: the restarted worker has an empty staticAssets map, /runtime/v1/@opendatacapture/runtime-internal/interactive/smiley.png goes to the server, and the image is broken.
Expected: the asset is served however long the task has been running.

Tests

packages/runtime-internal/src/interactive/__tests__/worker.test.ts: it('should still serve registered assets after the worker script is re-evaluated, so an idle termination does not lose them'). Load the assets, call vi.resetModules() and re-import worker.js to simulate a restart, then fetch. This needs a stubbed caches (Cache Storage) in the test globals.

e2e, in testing/src/specs/instrument-completion.spec.ts: open an interactive instrument with static assets, stop its service worker through CDP (ServiceWorker.stopWorker), then trigger an asset request and assert it loads.

Suggested fix

Persist the assets where a restarted worker can read them. On STATIC_ASSETS, write each one as a Response into a named Cache Storage cache (caches.open(...)), and acknowledge only after the writes resolve. In fetch, respond from caches.match(pathname) and fall back to the network on a miss. Clear the cache whenever a new STATIC_ASSETS message arrives, so one instrument's assets are never served to the next.

Dominant language
TypeScript
Stars
119
Forks
19
Avg merge
1d 2h
Merged PRs (30d)
56

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