mirror of
https://github.com/logos-messaging/nim-sds.git
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abdd40cc64
removal of persistency of retrievalHints because its never read. The PR also covers some leftovers of #72 - small interface and code style changes.
81 lines
3.5 KiB
Nim
81 lines
3.5 KiB
Nim
## Snapshot-based persistence interface (5 procs).
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##
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## Each protocol op issues AT MOST one `saveChannelMeta` and one
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## `updateHistory` call at the end of the op, under the channel lock. The
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## meta blob is the complete current per-channel state (lamport clock,
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## outgoing/incoming buffers, SDS-R repair buffers); the history update
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## carries (append, evict) for the message log. Bloom filter is rebuilt
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## from history on bootstrap, never persisted.
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##
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## Atomicity expectation: nim-sds issues `saveChannelMeta` and (when
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## non-empty) `updateHistory` back-to-back with NO intervening
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## `await`-of-other-work. The backend MAY treat the pair as one
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## transaction. The pair is keyed on the same `channelId`.
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##
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## Failure policy: a failed `saveChannelMeta` or `updateHistory` MUST NOT
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## abort the protocol op. The next op's save is fully self-contained and
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## will re-synchronise on-disk state. See PLAN_SNAPSHOT_PERSISTENCE.md §8.
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## `loadChannel` and `dropChannel` DO surface errors — they're the
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## durability-intent ops.
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import chronos, results
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import ./sds_message_id
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import ./channel_meta
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import ./history_update
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export results, sds_message_id, channel_meta, history_update
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type Persistence* = object
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## Pluggable durability backend. Supplied at `newReliabilityManager`
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## construction time; defaults to `noOpPersistence()` when not given.
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saveChannelMeta*: proc(
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channelId: SdsChannelID, meta: ChannelMeta
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): Future[Result[void, string]] {.async: (raises: []), gcsafe.}
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## Persist the complete current per-channel snapshot. Idempotent: the
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## blob is the full state, so a missed write is recovered by any later
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## successful write.
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updateHistory*: proc(
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channelId: SdsChannelID, update: HistoryUpdate
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): Future[Result[void, string]] {.async: (raises: []), gcsafe.}
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## Append newly-delivered messages and evict oldest ones past the
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## maxMessageHistory cap. Callers SHOULD skip this call entirely when
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## `update.isEmpty`.
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loadChannel*: proc(channelId: SdsChannelID): Future[Result[ChannelData, string]] {.
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async: (raises: []), gcsafe
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.}
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## Bootstrap on `getOrCreateChannel`. Returns the full prior state, or
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## an empty `ChannelData` if the channel is new on disk. Failure
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## propagates to the caller — bootstrap is a durability-intent op.
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dropChannel*: proc(channelId: SdsChannelID): Future[Result[void, string]] {.
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async: (raises: []), gcsafe
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.}
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## Wipe all persisted state for a channel. Called by `removeChannel` /
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## `resetReliabilityManager`. Backends SHOULD execute atomically.
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## Failure propagates to the caller — the caller asked us to confirm a
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## disk wipe and we cannot silently lie.
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proc noOpPersistence*(): Persistence =
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## Default backend: discards all writes, returns an empty snapshot on
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## load. Used when no real backend is supplied (existing tests and
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## non-durability-needing callers).
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Persistence(
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saveChannelMeta: proc(
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channelId: SdsChannelID, meta: ChannelMeta
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): Future[Result[void, string]] {.async: (raises: []).} =
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ok(),
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updateHistory: proc(
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channelId: SdsChannelID, update: HistoryUpdate
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): Future[Result[void, string]] {.async: (raises: []).} =
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ok(),
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loadChannel: proc(
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channelId: SdsChannelID
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): Future[Result[ChannelData, string]] {.async: (raises: []).} =
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ok(ChannelData.init()),
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dropChannel: proc(
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channelId: SdsChannelID
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): Future[Result[void, string]] {.async: (raises: []).} =
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ok(),
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)
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