Struct OutboxRelay 

#[non_exhaustive]
pub struct OutboxRelay {
    pub store: Arc<dyn OutboxStore>,
    pub publisher: Arc<dyn OutboxPublisher>,
    pub poll: Duration,
    pub batch: usize,
    pub leader: Option<(DistributedLock, Arc<dyn DLockBackend>)>,
}

Background poll → publish → ack loop. At-least-once: an entry is acked only after a successful publish, so a crash between the two replays it — consumers must dedupe on idempotency_key.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

store: Arc<dyn OutboxStore>

publisher: Arc<dyn OutboxPublisher>

poll: Duration

batch: usize

leader: Option<(DistributedLock, Arc<dyn DLockBackend>)>

Leader election: when set, only the replica holding this lock drains the outbox each tick — others skip silently. Eliminates duplicate publishing across a fleet (consumers still dedupe on idempotency_key for the at-least-once edge cases).

Implementations

impl OutboxRelay

pub fn new( store: Arc<dyn OutboxStore>, publisher: Arc<dyn OutboxPublisher>, ) -> Self

Defaults: 500ms poll, batch 32, no leader election.

pub fn poll(self, v: Duration) -> Self

pub fn batch(self, v: usize) -> Self

pub fn leader( self, lock: DistributedLock, backend: Arc<dyn DLockBackend>, ) -> Self

Enable leader election: only the lock holder drains each tick.

pub fn spawn(self)

Spawn the relay. Call from ArclyPlugin::on_start; the task dies with the runtime, so graceful shutdown needs no extra plumbing.

Drain-aware: once a shutdown signal flips the process drain flag the relay stops claiming new batches — pending rows are durable and the next leader picks them up. Backoff: consecutive fetch failures double the wait (up to 8× the poll interval) instead of hammering a struggling store at full poll rate.