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37 lines
2.6 KiB
Markdown
37 lines
2.6 KiB
Markdown
# Simplex.Messaging.Server.StoreLog
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> Append-only log for queue state changes: write, read/replay, compaction, crash recovery, backup retention.
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**Source**: [`StoreLog.hs`](../../../../../src/Simplex/Messaging/Server/StoreLog.hs)
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## writeStoreLogRecord — atomicity via manual write
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See comment in `writeStoreLogRecord`. `hPutStrLn` breaks writes larger than 1024 bytes into multiple system calls on `LineBuffered` handles, which could interleave with concurrent writes. The solution is manual `B.hPut` (single call for the complete record + newline) plus `hFlush`. `E.uninterruptibleMask_` prevents async exceptions between write and flush — ensures a complete record is always written.
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## readWriteStoreLog — crash recovery state machine
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The `.start` temp backup file provides crash recovery during compaction. The sequence:
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1. Read existing log, replay into memory
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2. Rename log to `.start` (atomic rename = backup point)
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3. Write compacted state to new file
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4. Rename `.start` to timestamped backup, remove old backups
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If the router crashes during step 3, the next startup detects `.start` and restores from it instead of the incomplete new file. Any partially-written current file is preserved as `.bak`. The comment says "do not terminate" during compaction — there is no safe interrupt point between steps 2 and 4.
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## removeStoreLogBackups — layered retention policy
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Backup retention is layered: (1) keep all backups newer than 24 hours, (2) of the rest, keep at least 3, (3) of those eligible for deletion, only delete backups older than 21 days. This means a router with infrequent restarts accumulates many backups (only cleaned on startup), while a frequently-restarting router keeps a rolling window. Backup timestamps come from ISO 8601 suffixes parsed from filenames.
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## QueueRec StrEncoding — backward-compatible parsing
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The `strP` parser handles two field name generations: old format `sndSecure=` (boolean, mapping `True` → `QMMessaging`, `False` → `QMContact`) and new format `queue_mode=`. Missing queue mode defaults to `Nothing` with the comment "unknown queue mode, we cannot imply that it is contact address." `EntityActive` status is implicit — not written to the log, and parsed as default when `status=` is absent.
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## openReadStoreLog — creates file if missing
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`openReadStoreLog` creates an empty file if it doesn't exist. Callers never need to handle "file not found."
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## foldLogLines — EOF flag for batching
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The `action` callback receives a `Bool` indicating whether the current line is the last one. This allows consumers (like `readQueueStore`) to batch operations and flush only on the final line.
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