StorageManager

navigator.storage requires a secure context (HTTPS or localhost) and is absent in some older or embedded browsers, so feature-detect before showing quota UI.

@inject Bit.Butil.StorageManager storageManager

if (await storageManager.IsSupported())
{
    // safe to query estimates and persistence
}

Estimate reports how many bytes the origin is currently using and roughly how many it may use in total, across all storage backends. The numbers are deliberately imprecise - browsers pad them to resist fingerprinting - but they are exactly what you need for a storage meter or a pre-download space check.

var estimate = await storageManager.Estimate();

// values in bytes; null when the runtime can't report them
var usage = estimate.Usage;
var quota = estimate.Quota;

if (usage is not null && quota is not null)
{
    var percent = (double)usage.Value / quota.Value * 100;
}

By default an origin's storage is best-effort: under disk pressure the browser may silently evict it. Persisted tells you which mode you are in - true means the data will survive until the user or the app explicitly deletes it.

var persisted = await storageManager.Persisted();
// false → best-effort storage, evictable under pressure

Persist asks the browser to upgrade the origin to persistent storage. The user agent decides: Chromium grants silently based on engagement heuristics (bookmarks, install state, notification permission), Firefox prompts the user. A false result is normal for a site the user has barely interacted with - it is a request, not a command.

var granted = await storageManager.Persist();

if (granted)
{
    // storage will not be evicted under pressure
}