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Routers

A Router groups one module's handlers with their own middleware and codec, and include_router mounts the group on a broker.

A router is a group of registrations bound to a broker type, not to a broker value, so a module builds it without a connection. include adds a #[subscriber] handler to the router the same way it adds one to a broker scope, settings included. A router's full type names every registration in a RouterDef, so a builder function returns impl RouterDef<B>, or Router<B, impl RouterDef<B>> when the caller still merges it. merge appends another router's registrations, and each router keeps its own codec and layers. include_router on a broker scope of the application mounts the group. layer adds middleware and is called before the router's first include; after one, .layer(..) applies to that registration alone. A router's layer must be a BlanketLayer, because the router hides its handlers' types. The app's own layers wrap outside the router's layers. Router layers wrap single-message handlers; batch handlers are not wrapped. with_codec switches the codec mid-chain: registrations already added keep the codec they were added with. Without it, a router decodes with the default codec, JSON when the json feature is on.

Example​

Each module returns its router, and the service merges them and mounts the result.

examples/routing.rs
#[subscriber("orders")]
async fn accept(order: &Order) -> HandlerOutcome {
    tracing::info!(order.id, "accepted");
    HandlerOutcome::ack()
}

#[subscriber("shipments")]
async fn dispatch(shipment: &Shipment) -> HandlerOutcome {
    tracing::info!(shipment.order_id, "dispatched");
    HandlerOutcome::ack()
}

/// The orders module's handlers.
fn orders() -> Router<MemoryBroker, impl RouterDef<MemoryBroker>> {
    Router::new().include(accept)
}

/// The shipping module's handlers.
fn shipping() -> Router<MemoryBroker, impl RouterDef<MemoryBroker>> {
    Router::new().include(dispatch)
}

fn app() -> impl App {
    RustStream::new(AppInfo::new("shop", "0.1.0")).with_broker(MemoryBroker::new(), |b| {
        b.include_router(orders().merge(shipping()));
    })
}

Middleware of one router​

Router::layer wraps every handler of the router, and nothing mounted outside it.

examples/routing.rs
/// Counts the deliveries of the handlers it wraps.
#[derive(Clone)]
struct Count(Arc<AtomicUsize>);

struct Counted<H> {
    inner: H,
    count: Arc<AtomicUsize>,
}

// A router hides its handlers' types, so its layer wraps a handler of any type.
impl BlanketLayer for Count {
    fn apply<M, C, S, H>(&self, handler: H) -> impl Handler<M, C, S> + 'static
    where
        M: Send + Sync + 'static,
        C: Send + 'static,
        S: Send + Sync + 'static,
        H: Handler<M, C, S> + 'static,
    {
        Counted {
            inner: handler,
            count: Arc::clone(&self.0),
        }
    }
}

impl<M, C, S, H> Handler<M, C, S> for Counted<H>
where
    M: Send + Sync,
    C: Send,
    S: Send + Sync,
    H: Handler<M, C, S>,
{
    async fn handle(&self, msg: &M, ctx: &mut Context<'_, C, S>) -> HandlerOutcome {
        self.count.fetch_add(1, Ordering::Relaxed);
        self.inner.handle(msg, ctx).await
    }
}

#[subscriber("orders")]
async fn accept(order: &Order) -> HandlerOutcome {
    tracing::info!(order.id, "accepted");
    HandlerOutcome::ack()
}

#[subscriber("shipments")]
async fn dispatch(shipment: &Shipment) -> HandlerOutcome {
    tracing::info!(shipment.order_id, "dispatched");
    HandlerOutcome::ack()
}

fn app(orders_seen: Arc<AtomicUsize>) -> impl App {
    RustStream::new(AppInfo::new("shop", "0.1.0")).with_broker(MemoryBroker::new(), |b| {
        // The layer comes first and wraps every handler of this router.
        b.include_router(Router::new().layer(Count(orders_seen)).include(accept));
        // Mounted on the scope, outside the router's layer.
        b.include(dispatch);
    })
}

A codec of one router​

Router::with_codec sets the codec the registrations after it decode with.

examples/routing.rs
#[subscriber("orders")]
async fn accept(order: &Order) -> HandlerOutcome {
    tracing::info!(order.id, "accepted");
    HandlerOutcome::ack()
}

/// The registrations after `with_codec` decode CBOR.
fn orders() -> impl RouterDef<MemoryBroker> {
    Router::new().with_codec(CborCodec).include(accept)
}

fn app() -> impl App {
    RustStream::new(AppInfo::new("shop", "0.1.0")).with_broker(MemoryBroker::new(), |b| {
        b.include_router(orders());
    })
}