probeWebStorageCapabilities function

Future<WebStorageCapabilities> probeWebStorageCapabilities({ bool requestPersist = false, })

Probes OPFS, worker sync handles, quota and optional Chromium-only APIs.

The worker handshake starts the page-wide OPFS worker (a Blob-URL dedicated worker); its result is cached for later file opens. requestPersist calls navigator.storage.persist() (Firefox shows a prompt, Chrome silently grants/denies).

Implementation

Future<WebStorageCapabilities> probeWebStorageCapabilities({
  bool requestPersist = false,
}) async {
  final filePrototype = _prototypeOfGlobal('FileSystemFileHandle');
  final syncHere = _hasFunction(filePrototype, 'createSyncAccessHandle');
  final createWritable = _hasFunction(filePrototype, 'createWritable');

  var opfs = false;
  int? quota;
  int? usage;
  var persisted = false;
  String? workerError;
  var syncInWorker = false;

  final storage = jsStorageManager;
  opfs = _hasFunction(storage, 'getDirectory');

  if (storage != null && opfs) {
    try {
      final estimate = await jsAwait(jsCall(storage, 'estimate'));
      if (estimate != null) {
        final object = estimate as JSObject;
        quota = jsInt(object['quota']);
        usage = jsInt(object['usage']);
      }
    } catch (_) {
      // estimate() is advisory; ignore failures.
    }
    try {
      persisted = jsBool(await jsAwait(jsCall(storage, 'persisted')));
    } catch (_) {
      // persisted() can be missing/blocked in exotic contexts.
    }
    if (requestPersist) {
      try {
        persisted = jsBool(await jsAwait(jsCall(storage, 'persist')));
      } catch (_) {
        // Not granted; keep the previous value.
      }
    }
    try {
      final pool = await OpfsWorkerPool.instance();
      final client = pool.manifest;
      final caps = client.capabilities ?? await client.hello();
      syncInWorker = caps.syncAccessHandle;
      if (!caps.opfs) {
        workerError = 'worker reports OPFS unavailable';
      }
    } catch (error) {
      workerError = '$error';
    }
  } else {
    workerError = 'navigator.storage.getDirectory is not available';
  }

  final navigator = jsNavigator;
  return WebStorageCapabilities(
    opfs: opfs,
    syncAccessHandleInWorker: syncInWorker,
    syncAccessHandleOnCurrentThread: syncHere,
    createWritable: createWritable,
    fileSystemPickers:
        _hasGlobal('showOpenFilePicker') && _hasGlobal('showSaveFilePicker'),
    fileSystemObserver: _hasGlobal('FileSystemObserver'),
    storageBuckets:
        navigator != null && navigator['storageBuckets'].isDefinedAndNotNull,
    sharedArrayBuffer: _hasGlobal('SharedArrayBuffer'),
    crossOriginIsolated: _protoBool(globalContext['crossOriginIsolated']),
    quotaBytes: quota,
    usageBytes: usage,
    persisted: persisted,
    workerError: workerError,
  );
}