Attribute Macro subscribe 

#[subscribe]

Register an async handler (#[photon::subscribe]). Marks a function as a subscription handler registered via inventory.

The host must call Photon::start_executor (Mode 1 hosts and Mode 2 workers) so inventory-registered handlers run. Publishers that only emit events can omit the executor.

Attribute	Purpose
topic = "…"	Topic name to consume (required)
durable = "name"	Checkpointed subscription name
group = "id"	Consumer-group load balancing

Full attribute reference: photon::config. Getting started: Mode 2 worker.

Usage (v1 — Box<dyn Actor>)

use photon::{topic, subscribe, Actor, Result};

#[topic(name = "user.notifications")]
pub struct NotificationPushed {
    pub user_id: String,
}

#[subscribe(topic = "user.notifications", durable = "push-worker")]
async fn on_notification(
    _actor: Box<dyn Actor>,
    _event: NotificationPushed,
) -> Result<()> {
    Ok(())
}

Actor bindings (v2)

The first parameter must be a simple identifier typed as one of:

• Box<dyn Actor> — reconstruct as-is (v1)
• Arc<dyn Actor> — Arc::from(reconstruct()?)
• Box<Concrete> / Arc<Concrete> — downcast via Actor::into_any; failure maps to PhotonError::Identity

Optional injectables (v2)

After (actor, payload) you may add trailing parameters detected by type path:

• &Event — transport event (metadata + raw JSON)
• HandlerCtx — delivery metadata (event_id, topic_name, topic_key, seq)

Unknown trailing types are rejected at compile time.

The handler must be async and return photon::Result<()>. Runnable: subscribe_v2.