utils/crdt_sync_dart/lib/src/device.dart
Krzysztof kuhy Rudnicki 6eef99d661
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Add DeviceIdentity and a legacy device id for the uuid migration
Groundwork for moving diet-guard, screen-locker and wake-alarm off fixed
role ids ('pc'/'phone'/'desktop') onto per-install uuids, the scheme todo
and home_inventory already use. A role constant collides the moment a
second machine takes the same role, and a reinstall silently inherits the
previous install's CRDT identity.

The migration cannot rewrite history: the device id is baked into every HLC
stamp already written, is the record path segment and the revision key. So
a device that has just switched ids must still recognise its former id as
its own -- otherwise skip-own-writes stops matching the old path, and the
device pulls back and re-merges its own pre-migration log as though a peer
had written it. Idempotent under LWW, but pure wasted transfer on every
tick.

Both halves therefore take an optional legacy id and test set membership
(own_ids / ownIds) rather than equality against a single id:

- crdt-sync (Python) 0.5.1 -> 0.6.0: new crdt_sync._device with
  DeviceIdentity + load_device_identity (generate-or-load, persisted); the
  mkdir is deliberately unguarded, since handing back an unpersisted id
  would mint a fresh uuid every restart and strand a device dir each time.
  sync_log gains legacy_device_id.
- crdt_sync_dart 0.6.0 -> 0.7.0: DeviceIdentity value type; syncLog gains
  legacyDeviceId. Persistence stays app-side, where the existing uuid apps
  already keep it in SharedPreferences under 'crdt.nodeId'.

Both changes are backward compatible: the parameter defaults to null, which
reproduces the previous single-id behaviour exactly.

Each half has a positive test and a negative control proving the old path
*is* pulled when no legacy id is declared -- so the skip is verified to be
the parameter's doing, not an artifact of the fixture.

Python: 239 tests, 100% branch coverage. Dart: 248 tests, analyzer clean,
device.dart 11/11 and sync.dart 57/57 lines covered.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GZH89WEqAjuJT8WZdqc7AP
2026-08-09 16:54:33 +02:00

52 lines
2.1 KiB
Dart

/// This device's stable sync identity.
library;
/// This device's current sync id, plus the id it used to push under before.
///
/// Every device that pushes into a namespace needs an id that is *its own*:
/// it is the directory segment its log is pushed under
/// (`<pathPrefix>/<deviceId>/<filename>`), the revision key, and the node
/// component baked into every HLC stamp it writes (`<iso>-<counter>-<id>`).
/// Two devices sharing an id overwrite each other's pushed file on every
/// tick, so the id must be per-*install*, not per-role.
///
/// A migration from a role constant (`phone`, `pc`, `desktop`) to a persisted
/// uuid cannot rewrite history: stamps already written keep the old id, and
/// the old path still holds the log pushed under it. So a device that has
/// just switched ids must still recognise its *former* id as itself -- which
/// is what [legacyId] carries, and why [ownIds] is a set. Skip-own-writes has
/// to test membership of that set rather than equality with one id, or the
/// device re-downloads and re-merges its own pre-migration history as though
/// a peer had written it.
class DeviceIdentity {
/// Creates an identity for [deviceId], optionally carrying a [legacyId].
const DeviceIdentity({required this.deviceId, this.legacyId});
/// The id to push, stamp and key revisions under from now on.
final String deviceId;
/// The id this device pushed under before migrating to a persisted uuid.
///
/// Null once the old path has been reclaimed.
final String? legacyId;
/// Every id that means "this device", for skip-own-writes checks.
Set<String> get ownIds => {deviceId, ?legacyId};
/// Whether [otherDeviceId] is one of this device's own ids.
bool isOwn(String otherDeviceId) => ownIds.contains(otherDeviceId);
@override
bool operator ==(Object other) =>
other is DeviceIdentity &&
other.deviceId == deviceId &&
other.legacyId == legacyId;
@override
int get hashCode => Object.hash(deviceId, legacyId);
@override
String toString() =>
'DeviceIdentity(deviceId: $deviceId, legacyId: $legacyId)';
}