peekExpired method
Up to limit keys whose expiry instant is at-or-before asOf
(default: now), in ascending-expiry order. limit: 1 answers
"which key is next to expire". limit: null means no limit —
the same set as getExpiredKeys, but with guaranteed
ascending-expiry ordering. Ties (same expiry instant) are
yielded in implementation-defined order.
Bounded counterpart to getExpiredKeys — use this for next-up probes and batched sweeps; the unbounded variant stays for the "drain everything" caller.
The returned Future completes once the backend has accepted
the request; the Stream then yields the keys (empty stream
if none match). Snapshot semantics as for nextExpiresAt.
Implementation
@override
@server
@client
Future<Stream<String>> peekExpired({DateTime? asOf, int? limit}) async {
final cutoff = asOf ?? DateTime.timestamp();
return Stream.fromIterable(
_collectAscending(expiresAt, limit, (t) => !t.isAfter(cutoff)));
}