ruststream 0.7.5

//! Middleware: a layer that drops a delivery naming no tenant, mounted for the whole app, for
//! one router, and for one registration. Each scenario is a test.
//!
//! ```text
//! cargo test --example layer --features testing,macros,memory,json
//! ```

// A plain build compiles the services; the tests that use them exist only in the test build.
#![cfg_attr(not(test), allow(dead_code, unused_imports))]

use ruststream::HeaderMap;
use ruststream::memory::prelude::*;
use ruststream::runtime::{BlanketLayer, Handler, Layer};
use serde::{Deserialize, Serialize};

#[derive(Debug, PartialEq, Deserialize, Serialize, Outgoing)]
struct Order {
    id: u64,
}

/// The headers of a delivery that names its tenant.
fn tenant(name: &'static str) -> HeaderMap {
    let mut headers = HeaderMap::new();
    headers.insert("tenant", name);
    headers
}

// --8<-- [start:layer]
/// Drops a delivery that names no tenant before the handler sees it.
#[derive(Clone)]
struct RequireTenant;

/// The handler `RequireTenant` makes of the one it wraps.
struct Tenanted<H>(H);

impl<H> Layer<H> for RequireTenant {
    type Handler = Tenanted<H>;

    fn layer(&self, inner: H) -> Tenanted<H> {
        Tenanted(inner)
    }
}

impl<M, C, S, H> Handler<M, C, S> for Tenanted<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 {
        if ctx.headers().get("tenant").is_none() {
            tracing::warn!(subscription = ctx.name(), "no tenant header, dropped");
            return HandlerOutcome::drop();
        }
        self.0.handle(msg, ctx).await
    }
}

// The app and a router wrap handlers whose types they hide, through this generic method.
impl BlanketLayer for RequireTenant {
    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,
    {
        Tenanted(handler)
    }
}
// --8<-- [end:layer]

mod app_wide {
    use std::error::Error;

    use ruststream::memory::prelude::*;
    use ruststream::testing::{Outcome, TestApp};

    use super::{Order, RequireTenant, tenant};

    // --8<-- [start:app]
    #[subscriber("orders")]
    async fn accept(order: &Order) -> HandlerOutcome {
        tracing::info!(order.id, "accepted");
        HandlerOutcome::ack()
    }

    fn app() -> impl App {
        RustStream::new(AppInfo::new("orders", "0.1.0"))
            // Every handler the app mounts below runs inside the layer.
            .layer(RequireTenant)
            .with_broker(MemoryBroker::new(), |b| {
                b.include(accept);
            })
    }
    // --8<-- [end:app]

    #[tokio::test]
    async fn an_order_without_a_tenant_is_dropped() -> Result<(), Box<dyn Error>> {
        let tb = TestApp::start(app()).await?;
        let broker = tb.broker::<MemoryBroker>();
        let order = Order { id: 7 };
        broker.message(&order).to("orders").publish().await?;
        broker
            .message(&order)
            .with_headers(tenant("acme"))
            .to("orders")
            .publish()
            .await?;

        let outcomes = broker.subscriber("orders").outcomes();
        assert_eq!(outcomes, [Outcome::Drop, Outcome::Ack]);
        Ok(())
    }
}

mod scopes {
    use std::error::Error;

    use ruststream::memory::prelude::*;
    use ruststream::testing::TestApp;

    use super::{Order, RequireTenant};

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

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

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

    // --8<-- [start:scopes]
    fn app() -> impl App {
        RustStream::new(AppInfo::new("billing", "0.1.0")).with_broker(MemoryBroker::new(), |b| {
            // Before the first `include`: every handler of this router.
            b.include_router(Router::new().layer(RequireTenant).include(refund));
            // After an `include`: that registration alone; `audit` runs unwrapped.
            b.include_router(
                Router::new()
                    .include(invoice)
                    .layer(RequireTenant)
                    .include(audit),
            );
        })
    }
    // --8<-- [end:scopes]

    #[tokio::test]
    async fn only_the_wrapped_handlers_drop_an_untenanted_order() -> Result<(), Box<dyn Error>> {
        let tb = TestApp::start(app()).await?;
        let broker = tb.broker::<MemoryBroker>();
        let order = Order { id: 7 };
        for channel in ["refunds", "invoices", "audit"] {
            broker.message(&order).to(channel).publish().await?;
        }

        broker.subscriber("refunds").settled(HandlerOutcome::drop());
        broker
            .subscriber("invoices")
            .settled(HandlerOutcome::drop());
        broker.subscriber("audit").settled(HandlerOutcome::ack());
        Ok(())
    }
}

// The scenarios are the tests above; the command in the header runs them.
fn main() {}