Evgeny @ SimpleX Chat
1.6 KiB
Simplex.Messaging.Notifications.Server.Store
STM-based in-memory store for notification tokens, subscriptions, and last-notification accumulation.
Source: Notifications/Server/Store.hs
Non-obvious behavior
1. Two-level token registration index
tokenRegistrations uses a nested TMap: DeviceToken -> TMap ByteString NtfTokenId, where the inner key is the serialized verify key. This allows multiple concurrent registrations per device token (with different keys), protecting against malicious registration attempts if a token is compromised. The inner key is derived via C.toPubKey C.pubKeyBytes.
2. stmRemoveInactiveTokenRegistrations cleans up rivals
When a token is activated, stmRemoveInactiveTokenRegistrations removes ALL other registrations for the same device token, including their token records, last notifications, and all subscriptions. Only the activating token's registration survives.
3. stmStoreTokenLastNtf guards against stale tokens
stmStoreTokenLastNtf performs a non-STM IO lookup first, then enters STM. Within the STM block, it re-checks the map to handle the race where another thread modified the map between the IO lookup and STM entry. It only inserts for tokens that exist in the tokens map — stale token IDs are silently ignored.
4. tokenLastNtfs accumulates via prepend
New notifications are prepended to the NonEmpty PNMessageData list via (<|). The list is unbounded in the STM store — bounding is handled at the push delivery layer (the Postgres store limits to 6).