Crate open_wal 

open-wal — a focused, embeddable, single-writer append-only write-ahead log for an LMAX-style, event-sourced system.

Durability-first: a committed record survives process crash and power loss on honest hardware. The WAL stores opaque byte payloads — serialization is entirely the caller’s concern. It is not a database, not multi-writer, and runs no background threads.

The normative design lives in docs/wal_design_v6.md; the durability invariants D1–D12 there are binding on every change.

This crate is built in milestones (§13). M0 (foundations) provides the core value types — Lsn, WalConfig, WalError — and the CRC-32C checksum ([crc32c]). M1 adds the internal record codec (record — encode/decode of the §5.3 framing). M2 adds the single-segment write path and replay: Wal::open/append/commit, a streaming Reader, the DurabilityObserver hook, segment pre-allocation and fdatasync, and a zero-allocation hot path. M3 adds intra-segment crash recovery (torn-tail detection + durable zeroing, fatal mid-log corruption). M4 adds the multi-segment write path — segment roll, commit-time whole-record split, sealed-segment immutability — and multi-segment recovery (discovery, cross-segment continuity, crash-during-roll handling). Checkpoint/retention (M5) arrives later.

Structs

Lsn

Log Sequence Number. Newtype to prevent mixing with byte offsets/counts.

NullObserver

The default observer: a verified no-op that inlines to nothing.

Reader

Streaming reader over the log, starting at a caller-chosen LSN.

RecoveryReport

Outcome of recovery, returned by Wal::open (§6).

Wal

Single-writer, append-only write-ahead log handle.

WalConfig

Configuration for a WAL instance.

Enums

TailState

State of the active segment’s tail after recovery (§6).

WalError

All error conditions surfaced by the WAL.

Traits

DurabilityObserver

Notified after each successful durability advance, on the writer thread.

Functions

crc32c

Compute the CRC-32C (Castagnoli) checksum of data.

Type Aliases

Result

Convenience alias for results returned by this crate.