Struct WriteAheadLog 

pub struct WriteAheadLog {
    pub prev_dag_hash: [u8; 32],
    /* private fields */
}

The Write-Ahead Log (WAL) ensures mobile fault tolerance by appending all 48-byte Quin mutations directly to flash memory synchronously before they are packed into the larger 40KB SuperBlock structures.

The WAL also maintains a prev_dag_hash linking each checkpoint into the git_bridge::DagStore Merkle-DAG so the full write history is content-addressed.

Fields

prev_dag_hash: [u8; 32]

SHA-256 of the most recent DagNode committed from this WAL. [0u8; 32] means no prior checkpoint — next call to checkpoint_to_dag triggers genesis_node.

Implementations

impl WriteAheadLog

pub fn open<P: AsRef<Path>>(path: P) -> Result<Self>

Opens or creates the append-only WAL file at path.

If the file already has a 32-byte header (prior checkpoint hash), it is read back so the chain is preserved across restarts.

pub fn append_mutation(&mut self, quin: &NQuin) -> Result<()>

Synchronously appends a NQuin to the log and flushes to disk. This prevents data loss if the OS kills the process.

pub fn append_mutation_volatile(&mut self, quin: &mut NQuin) -> Result<()>

Append with volatile field scrub after durable sync (wipes transient reasoning state).

pub fn recover(&mut self) -> Result<Vec<NQuin>>

Reconstructs uncommitted NQuins from the WAL (skips the 32-byte header).

pub fn truncate(&mut self) -> Result<()>

Wipes the NQuin region of the WAL after a SuperBlock commit, preserving the header.

Call checkpoint_to_dag before this so the hash chain is updated first.

pub fn checkpoint_to_dag( &mut self, dag_store: &mut DagStore, author_did: u64, timestamp_ms: u64, ) -> Result<[u8; 32]>

Commit the current WAL contents as a DagNode, updating prev_dag_hash.

If the WAL is empty (no quins since the last checkpoint), this is a no-op and returns the existing prev_dag_hash.

Typical call sequence:

wal.checkpoint_to_dag(&mut dag_store, author_did, now_ms())?;
wal.truncate()?;

pub fn buffered_count(&mut self) -> Result<usize>

Return the number of NQuin records currently buffered in the WAL.