Channels

A subscription is a channel the service receives on, and a topic a channel it sends to; neither carries a googlepubsub binding.

A channel the service receives on is named after the subscription. The topic behind a subscription is a fact of the service's infrastructure, which the document, built before anything connects, does not see. A channel the service publishes to reports the topic the mount site resolved as its address: a reply type's #[outgoing(name)], a reply("dest") clause, or a slot's destination. The channel binding of googlepubsub describes a topic's configuration: labels, retention, storage policy and schema. No descriptor or publish policy holds those, so channels carry no binding.

Example

The subscription orders-workers is a channel the service receives on, and the topic receipts one it sends to.

Macros

examples/pubsub_asyncapi.rs

/// The subscription `orders-workers` is a channel the service receives on, and the topic
/// `receipts` a channel it sends to.
#[subscriber(GooglePubSub::new("orders-workers"), reply)]
async fn receipt(order: &Order) -> Receipt {
    Receipt { order_id: order.id }
}

Manual

examples/manual/pubsub_asyncapi.rs

/// The subscription `orders-workers` is a channel the service receives on, and the topic
/// `receipts` a channel it sends to.
struct ReceiptFor;

impl Handle<Order, Receipt> for ReceiptFor {
    fn handle(
        &self,
        order: &Order,
        _outs: &(),
        _ctx: &mut Context<'_>,
    ) -> impl Future<Output = Result<Receipt, HandlerOutcome>> {
        ready(Ok(Receipt { order_id: order.id }))
    }
}

fn orders() -> GooglePubSub {
    GooglePubSub::new("orders-workers")
}