baukit-push

baukit-push delivers notifications to devices through a provider-neutral PushSender port and ships one adapter for it, ExpoPushSender. Domain code builds PushMessage values and reads PushOutcome values; nothing above the port names Expo. A DeviceRegistry port stores which tokens belong to which owner, and a separate DeliveryClaimStore keeps scheduled pushes at most once per owner, local date, and kind. Deciding who gets notified and when, the copy, quiet hours, and the channel stay in the product.

The crate is opt-in. It is not part of the generated backend template and is not wired into baukit_config::BaukitConfig.

The port

pub trait PushSender: Send + Sync {
    fn send<'a>(&'a self, batch: Vec<PushMessage>) -> PushFuture<'a>;
}

One call takes a whole batch. The adapter splits it into provider-sized chunks itself, so callers do not manage batching. Outcomes cover every message in the batch but arrive in no guaranteed order; match them to messages by token.

PushMessage carries a DeviceToken, a title, a body, an ordered data map delivered with the notification, and an optional channel_id that Android reads to pick a notification channel. PushOutcome carries the same DeviceToken, so logging ?outcome or ?message prints DeviceToken(<redacted>) instead of the token.

Two-phase Expo delivery

Expo does not confirm delivery in the send response. /push/send answers with one ticket per notification, meaning only that Expo accepted it. Delivery is confirmed later through /push/getReceipts. ExpoPushSender runs both phases per chunk, which collapses into three delivery states:

Accepted is neither success nor failure. The notification is in flight, so never resend on it. Its ticket ID is what a later receipt poll asks about; see Deferred receipts.

Rejection vocabulary

Expo's error codes map onto PushRejection:

An unrecognized code keeps Expo's own string rather than being dropped, so a new provider code shows up in logs instead of vanishing into a generic failure.

Device registry

A device token stops working once the app is uninstalled or the user turns notifications off. Expo reports that as DeviceNotRegistered, and the same failure repeats on every send until the token is gone. The DeviceRegistry port owns the tokens and removes dead ones in one call after each send:

use baukit_push::{DeviceRegistry, PushMessage, PushSender};
use chrono::Utc;

async fn deliver(
    sender: &impl PushSender,
    registry: &impl DeviceRegistry,
    messages: Vec<PushMessage>,
) -> Result<u64, Box<dyn std::error::Error>> {
    let sent_at = Utc::now();
    let outcomes = sender.send(messages).await?;
    Ok(registry.invalidate_dead_tokens(&outcomes, sent_at).await?)
}

invalidate_dead_tokens removes only tokens whose outcome is_token_dead, which is true only for DeviceNotRegistered. Every other rejection describes the notification, not the token, so deleting on MessageTooBig would throw away a working device. A device registered again after sent_at keeps its token, because Expo's verdict predates the new registration. Outcomes without a dead token cost no store round trip.

Each owner keeps at most DEFAULT_DEVICES_PER_OWNER (10) devices unless the store is built with with_devices_per_owner. A registration over the cap evicts the owner's devices with the oldest last_registered_at, breaking ties on created_at and then on the token, and reports how many went in RegistrationOutcome::evicted. The device being registered is never evicted, even when its instant is older than the others. Rotating removes the predecessor first, so rotating at the cap evicts nothing.

DeviceToken accepts 1 to 512 bytes of visible ASCII. Its Debug output is redacted and it has no Display; read it with expose only where it goes to the provider or the store. PushValidationError and PushStoreError never contain a token. DeviceTimeZone checks the shape of an IANA name only, so resolve it with a time zone database before registering if the product schedules by it. DevicePlatform is Ios or Android.

PostgreSQL store

The sqlx-postgres feature adds PostgresDeviceRegistry over the table in POSTGRES_PUSH_DEVICES_MIGRATION_SQL, which is available without the feature. Copy the SQL into the product's migrations and add the owner foreign key the header shows, with ON DELETE CASCADE. Nothing migrates on startup.

[dependencies]
baukit-push = { workspace = true, features = ["sqlx-postgres"] }

The token is the primary key. register and rotate run in one transaction under a per-owner advisory lock, so concurrent registrations cannot overshoot the cap. erase_owner_push_devices takes any PgExecutor and runs inside the product's erasure transaction when the owner row stays or no foreign key exists.

Daily delivery claims

A scheduled sender claims a DeliveryClaim keyed by owner, local date, and DeliveryKind before it sends. claim returns false when another worker already holds it. If the whole send fails, release the claim so a later run can try again. Event-driven senders do not need claims, which is why this is a separate DeliveryClaimStore port with its own table.

let claim = DeliveryClaim::new(owner_id, local_date, DeliveryKind::new("daily_reminder")?);
if !claims.claim(claim.clone(), Utc::now()).await? {
    return Ok(());
}
let sent_at = Utc::now();
match sender.send(messages).await {
    Ok(outcomes) => {
        registry.invalidate_dead_tokens(&outcomes, sent_at).await?;
    }
    Err(error) => {
        claims.release(claim).await?;
        return Err(error.into());
    }
}

A DeliveryKind is 1 to 64 bytes of [a-z0-9_.-] starting with a letter or digit. With sqlx-postgres, PostgresDeliveryClaimStore uses the table in POSTGRES_PUSH_DELIVERY_CLAIMS_MIGRATION_SQL. erase_owner_delivery_claims removes one owner's claims, and purge_delivery_claims deletes one bounded batch of claims for local dates before a cutoff; call it until it returns less than the batch size.

Deferred receipts

ExpoPushSender asks for receipts right after the send, and Expo often has not settled them yet. Those notifications come back as Accepted(ticket). A DeviceNotRegistered that Expo settles later would otherwise go unnoticed until the next send to that token. Expo recommends checking receipts 15 minutes after the send, keeps them for 24 hours, and takes at most 1000 ticket IDs per getReceipts request (MAX_RECEIPT_BATCH_SIZE; the adapter splits larger lists itself).

Record the accepted tickets after each send:

use baukit_push::{DeviceRegistry, PendingReceiptStore, PushMessage, PushSender};
use chrono::Utc;

async fn deliver(
    sender: &impl PushSender,
    registry: &impl DeviceRegistry,
    pending: &impl PendingReceiptStore,
    messages: Vec<PushMessage>,
) -> Result<(), Box<dyn std::error::Error>> {
    let sent_at = Utc::now();
    let outcomes = sender.send(messages).await?;
    registry.invalidate_dead_tokens(&outcomes, sent_at).await?;
    pending.record_accepted(&outcomes, sent_at).await?;
    Ok(())
}

record_accepted stores ticket ID, token, and sent_at for every Accepted outcome, first due RECEIPT_POLL_DELAY (15 minutes) after the send. poll_pending_receipts then does one bounded run:

1. take_due takes up to limit due tickets and makes them due again one RECEIPT_POLL_DELAY later, so concurrent pollers take disjoint batches and an unsettled ticket goes to the back of the queue.
2. It reads their receipts through the PushReceiptSource port, which ExpoPushSender implements.
3. It passes each DeviceNotRegistered token to DeviceRegistry::invalidate with the sent_at of its own send, so a device registered again after that send keeps its token.
4. It deletes the settled tickets. Tickets without a receipt stay for a later run.

The returned ReceiptPoll counts the tickets taken and settled and the tokens invalidated. Fewer taken than limit means nothing else is due. A failure is a ReceiptPollError; the taken tickets stay recorded and come due again. purge deletes tickets older than RECEIPT_RETENTION (24 hours), whose receipts Expo no longer has.

Baukit ships no scheduler. Drive the poll from the product's job runner, for example a baukit-jobs handler that a FixedUtcInterval re-enqueues every few minutes:

use std::num::NonZeroU32;

use baukit_jobs::{ClaimedJob, JobCancellation, JobError, JobFuture, JobHandler};
use baukit_push::{
    ExpoPushSender, PendingReceiptStore, PostgresDeviceRegistry, PostgresPendingReceiptStore,
    RECEIPT_RETENTION, ReceiptPollError, poll_pending_receipts,
};
use chrono::Utc;

const RECEIPT_BATCH: NonZeroU32 = NonZeroU32::new(1000).expect("not zero");

struct PollPushReceipts {
    sender: ExpoPushSender,
    pending: PostgresPendingReceiptStore,
    registry: PostgresDeviceRegistry,
}

impl JobHandler for PollPushReceipts {
    fn job_types(&self) -> &'static [&'static str] {
        &["push_receipts.poll"]
    }

    fn handle<'a>(
        &'a self,
        _job: &'a ClaimedJob,
        _cancellation: JobCancellation,
    ) -> JobFuture<'a, Result<(), JobError>> {
        Box::pin(async move {
            let now = Utc::now();
            self.pending
                .purge(now - RECEIPT_RETENTION, RECEIPT_BATCH)
                .await
                .map_err(|error| JobError::retryable(error.to_string()))?;
            loop {
                let poll = poll_pending_receipts(
                    &self.sender,
                    &self.pending,
                    &self.registry,
                    now,
                    RECEIPT_BATCH,
                )
                .await
                .map_err(job_error)?;
                if poll.taken < u64::from(RECEIPT_BATCH.get()) {
                    return Ok(());
                }
            }
        })
    }
}

fn job_error(error: ReceiptPollError) -> JobError {
    match &error {
        ReceiptPollError::Push(push) => match push.retry_after() {
            Some(delay) => JobError::retryable_after(error.to_string(), delay),
            None => JobError::retryable(error.to_string()),
        },
        ReceiptPollError::Store(_) => JobError::retryable(error.to_string()),
    }
}

The loop ends because every taken ticket moves past now. With sqlx-postgres, PostgresPendingReceiptStore uses the table in POSTGRES_PUSH_PENDING_RECEIPTS_MIGRATION_SQL. The table has no owner column; a row holds a token for at most the retention window until purge removes it.

Retries

A failure that stops the whole request is a PushError::Transport carrying a baukit_http::RetryClass, the same classification the other outbound clients use. An Expo rate limit that names a Retry-After reaches the caller as a concrete delay:

# use std::time::Duration;
# fn example(error: &baukit_push::PushError) {
if error.is_retryable() {
    let delay = error.retry_after().unwrap_or(Duration::from_secs(30));
    // schedule the batch again after `delay`
}
# }

A malformed provider response is a PushError::InvalidResponse and is never retryable. Per-notification refusals are not errors at all; check PushRejection::is_retryable on each outcome instead.

Configuration

PushConfig is a Deserialize + baukit_config::Validate section a product embeds in its own product config, which puts environment overrides on the usual nested path (ORDERS__PUSH__BATCH_SIZE).

PushOptions::from_config validates the whole section at once and reports every problem together, so a bad base URL or batch size fails at startup instead of on the first notification. In code, build options directly:

use std::time::Duration;

use baukit_push::{ExpoPushSender, PushOptions};

# fn build() -> Result<ExpoPushSender, baukit_push::PushOptionsError> {
let options = PushOptions::default()
    .with_batch_size(50)?
    .with_request_timeout(Duration::from_secs(5))?;
ExpoPushSender::with_options(options)
# }

Pass the full send URL to PushOptions::new, including /push/send. This also works for local mock servers and proxies with a different path prefix.

Expo only requires an access token when the project enforces push security. Set one with with_access_token and it is sent as a bearer header; Debug output redacts it.

Testing

Enable the test-support feature for FakePushSender, an in-memory recording sender and receipt source, and for MemoryDeviceRegistry, MemoryDeliveryClaimStore, and MemoryPendingReceiptStore, which follow the PostgreSQL adapters' rules:

[dev-dependencies]
baukit-push = { workspace = true, features = ["test-support"] }

Every token delivers by default. Script exceptions per token with reject and accept_without_receipt, settle an accepted token's later receipt with settle_receipt, or fail every send and receipt request with fail_with. Read back what a service under test sent through batches, messages, outcomes, dead_tokens, and receipt_requests. Clones share one recording, so a clone handed to a service still reports its sends.

The fake lives here rather than in baukit-test because it would otherwise pull this opt-in crate into the dependencies of every product that uses the test kit.