ruststream_lapin/queue/

quorum.rs

//! The quorum queue descriptor.

use std::num::NonZeroU16;
use std::time::Duration;

use lapin::types::{AMQPValue, FieldTable};
#[cfg(feature = "asyncapi")]
use ruststream::asyncapi::Bindings;
use ruststream::runtime::IntoSource;
use ruststream::{BrokerMoves, RetryDeclaration, SubscriptionSource};

use super::spec::{
    Binding, DEAD_LETTER_EXCHANGE, DEAD_LETTER_ROUTING_KEY, DELIVERY_LIMIT, QueueKind, QueueSpec,
    queue_settings,
};
use crate::broker::ConnectedLapinBroker;
use crate::delay::Delay;
use crate::error::AmqpError;
use crate::exchange::RabbitExchange;
use crate::subscriber::LapinSubscriber;

/// Describes one quorum-queue subscription: the queue, its expected settings, and its bindings.
///
/// A quorum queue counts the deliveries a message has spent and ends a poison loop itself: with
/// an `x-delivery-limit` and a dead-letter route it carries a message away once its deliveries
/// run out, whether or not a service is running to count them. So the retries of a registration
/// mounted here are the broker's, and `out_retry(policy)` does not compile on it: the server moves
/// the spent message, and the service publishes no copy. A registration declares the pair at the mount site:
///
/// ```
/// use ruststream_lapin::prelude::*;
/// use serde::Deserialize;
///
/// #[derive(Deserialize)]
/// struct Payout {
///     id: u64,
/// }
///
/// #[subscriber(RabbitQuorumQueue::new("payouts"))]
/// async fn on_payout(payout: &Payout) -> HandlerOutcome {
///     tracing::warn!(payout.id, "the bank refused, trying again");
///     HandlerOutcome::retry()
/// }
///
/// fn app() -> RustStream {
///     let broker = LapinBroker::new("amqp://localhost:5672").declare_topology(true);
///     RustStream::new(AppInfo::new("payouts", "0.1.0")).with_broker(broker, |b| {
///         // The server applies this cap: it becomes the queue's delivery limit and dead-letter
///         // route.
///         b.include(on_payout)
///             .max_attempts(nonzero!(5u32))
///             .dead_letter("payouts.dead");
///     })
/// }
/// ```
///
/// The pair becomes this queue's `x-delivery-limit` and dead-letter route when the broker opts
/// into [`declare_topology(true)`](crate::LapinBroker::declare_topology). A queue declared
/// elsewhere carries its own arguments, so subscribing then refuses the declaration rather than
/// promising a cap nothing applies; configure the queue on the broker and mount it without the
/// pair. The crate reads the queue's count either way.
///
/// A quorum queue is durable, shared and permanent by definition, so those three settings are not
/// here to be set wrong. For the single-node implementation take [`RabbitQueue`](crate::RabbitQueue).
///
/// # Examples
///
/// ```
/// use ruststream_lapin::prelude::*;
/// use serde::Deserialize;
///
/// #[derive(Deserialize)]
/// struct Charge {
///     id: u64,
/// }
///
/// // A charge the payment provider keeps refusing is moved to `dead-letters` by the server after
/// // its fifth delivery: the limit counts the four returns it survives.
/// #[subscriber(RabbitQuorumQueue::new("charges")
///     .bind(RabbitExchange::topic("events"), "charge.*")
///     .dead_letter_exchange("dead-letters")
///     .delivery_limit(4))]
/// async fn take_payment(charge: &Charge) -> HandlerOutcome {
///     tracing::info!(charge.id, "charging");
///     HandlerOutcome::retry()
/// }
///
/// fn app() -> RustStream {
///     let broker = LapinBroker::new("amqp://localhost:5672").declare_topology(true);
///     RustStream::new(AppInfo::new("payments", "0.1.0")).with_broker(broker, |b| {
///         b.include(take_payment);
///     })
/// }
/// ```
#[derive(Debug, Clone, PartialEq)]
pub struct RabbitQuorumQueue {
    spec: QueueSpec,
    retry: RetryDeclaration,
}

impl RabbitQuorumQueue {
    /// Describes the quorum queue `name`.
    #[must_use]
    pub fn new(name: impl Into<String>) -> Self {
        Self {
            spec: QueueSpec::new(QueueKind::Quorum, name.into()),
            retry: RetryDeclaration::new(),
        }
    }

    /// How often the queue returns a message before it carries it away (`x-delivery-limit`).
    ///
    /// The argument counts the returns a message survives, so it is one less than the number of
    /// deliveries the queue allows: `delivery_limit(2)` hands a message out three times. Where it
    /// goes then is [`dead_letter_exchange`](Self::dead_letter_exchange); a limit with no
    /// dead-letter route drops the spent message instead.
    ///
    /// This is the queue's own policy, for a queue whose retries are not one registration's
    /// business. A mount site that declares `max_attempts(n).dead_letter(..)` is the more specific
    /// statement and is written over this.
    #[must_use]
    pub fn delivery_limit(mut self, returns: u32) -> Self {
        self.spec
            .set(DELIVERY_LIMIT, AMQPValue::LongLongInt(i64::from(returns)));
        self
    }

    pub(crate) const fn spec(&self) -> &QueueSpec {
        &self.spec
    }

    /// What the mount site declared about this registration's retries, applied when the queue is
    /// declared.
    pub(crate) const fn retry(&self) -> &RetryDeclaration {
        &self.retry
    }

    /// Refuses a declaration the queue cannot carry, before the subscription opens.
    ///
    /// A native dead-letter policy needs both halves, and both halves need a queue this service
    /// declares - a queue declared elsewhere carries the arguments whoever declared it gave it.
    /// Neither is knowable before the broker is configured, which is why this is a startup error
    /// and not a compile error.
    pub(crate) fn check_retry(&self, declares_topology: bool) -> Result<(), AmqpError> {
        match (self.retry.max_attempts(), self.retry.dead_letter()) {
            // Both halves, on a queue this service declares: the declaration becomes arguments.
            (Some(_), Some(_)) if declares_topology => Ok(()),
            // Nothing declared: the queue keeps whatever policy it was given.
            (None, None) => Ok(()),
            (Some(_), None) => Err(AmqpError::InvalidOptions(format!(
                "quorum queue {:?} was mounted with `max_attempts(..)` and no `dead_letter(..)`: \
                 the queue carries a spent delivery away only when it knows where to, and a \
                 delivery limit on its own drops it. Declare both at the mount site, or neither \
                 and let the queue keep its own policy",
                self.name(),
            ))),
            (None, Some(_)) => Err(AmqpError::InvalidOptions(format!(
                "quorum queue {:?} was mounted with `dead_letter(..)` and no `max_attempts(..)`: \
                 nothing tells the queue when a delivery is spent, so the destination is never \
                 reached. Declare both at the mount site, or neither and let the queue keep its \
                 own policy",
                self.name(),
            ))),
            (Some(_), Some(_)) => Err(AmqpError::InvalidOptions(format!(
                "quorum queue {:?} applies `max_attempts(..).dead_letter(..)` as its own \
                 arguments, and this service does not declare it. Enable \
                 `declare_topology(true)`, or configure `x-delivery-limit` and \
                 `x-dead-letter-exchange` on the queue itself and mount the handler without the \
                 pair",
                self.name(),
            ))),
        }
    }
}

queue_settings!(RabbitQuorumQueue);

/// The descriptor is its own source, so the manual path's `subscriber(source, body)` takes a
/// `RabbitQuorumQueue` where the attribute path writes it in the decorator.
impl IntoSource for RabbitQuorumQueue {
    type Source = Self;

    fn into_source(self) -> Self {
        self
    }
}

impl SubscriptionSource<ConnectedLapinBroker> for RabbitQuorumQueue {
    type Subscriber = LapinSubscriber;

    /// The queue moves a spent delivery itself: its `x-delivery-limit` counts the deliveries and
    /// its dead-letter route takes the message that runs out of them, with nothing published by
    /// this process. That is what makes `out_retry(policy)` a compile error here, and what keeps
    /// the cap holding while the service is down.
    type Copies = BrokerMoves;

    fn name(&self) -> &str {
        &self.spec.name
    }

    async fn subscribe(
        self,
        connected: &ConnectedLapinBroker,
    ) -> Result<Self::Subscriber, AmqpError> {
        connected.subscribe(self).await
    }

    /// Takes the registration's cap and dead-letter destination into the descriptor, so the queue
    /// this broker declares carries them as topology.
    fn declare_retry(mut self, declaration: &RetryDeclaration) -> Self {
        self.retry = declaration.clone();
        self
    }

    /// The queue this subscription consumes, as the `amqp` binding names its settings.
    #[cfg(feature = "asyncapi")]
    fn channel_bindings(&self) -> Bindings {
        crate::bindings::queue_channel(&self.spec)
    }

    /// The consumer's own half: this crate acknowledges by hand on every subscription.
    #[cfg(feature = "asyncapi")]
    fn operation_bindings(&self) -> Bindings {
        crate::bindings::consumer_operation()
    }
}

#[cfg(test)]
mod tests {
    use lapin::types::{AMQPValue, ShortString};
    use ruststream::{RetryDeclaration, SubscriptionSource, nonzero};

    use super::RabbitQuorumQueue;
    use crate::broker::ConnectedLapinBroker;
    use crate::queue::spec::declared_arguments;

    // What the mount site declared reaches the queue as topology: a delivery limit one short of
    // the cap, and a dead-letter route to the destination on the default exchange.
    #[test]
    fn a_declaration_becomes_the_quorum_queues_arguments() {
        let declaration = RetryDeclaration::new()
            .with_max_attempts(nonzero!(3u32))
            .with_dead_letter("orders.dead");
        let queue = <RabbitQuorumQueue as SubscriptionSource<ConnectedLapinBroker>>::declare_retry(
            RabbitQuorumQueue::new("orders.quorum"),
            &declaration,
        );

        let arguments = declared_arguments(queue.spec(), Some(queue.retry()));

        let argument = |name: &str| arguments.inner().get(&ShortString::from(name)).cloned();
        assert_eq!(
            argument("x-queue-type"),
            Some(AMQPValue::LongString("quorum".into()))
        );
        assert_eq!(
            argument("x-delivery-limit"),
            Some(AMQPValue::LongLongInt(2))
        );
        assert_eq!(
            argument("x-dead-letter-exchange"),
            Some(AMQPValue::LongString(String::new().into()))
        );
        assert_eq!(
            argument("x-dead-letter-routing-key"),
            Some(AMQPValue::LongString("orders.dead".into()))
        );
    }
}