Events

Define and use custom events in Rust

Defining Custom Events

use blazen::prelude::*;

#[derive(Debug, Clone, Serialize, Deserialize, Event)]
struct AnalyzeEvent {
    text: String,
    score: f64,
}

The #[derive(Event)] macro generates event_type(), serialization, and routing support.

Built-in Events

• StartEvent — carries data: serde_json::Value, triggers workflow start
• StopEvent — carries result: serde_json::Value, terminates workflow
• InputRequestEvent — requests human input, auto-pauses workflow
• InputResponseEvent — carries human response, matched by request_id

Event Flow

Steps declare their input/output types:

#[step]
async fn analyze(event: StartEvent, _ctx: Context) -> Result<AnalyzeEvent, WorkflowError> {
    Ok(AnalyzeEvent {
        text: event.data["text"].as_str().unwrap().into(),
        score: 0.95,
    })
}

The router matches event types to steps automatically.

Multiple Output Events

Use #[step(emits = [...])] and StepOutput:

#[step(emits = [PositiveEvent, NegativeEvent])]
async fn route(event: AnalyzeEvent, _ctx: Context) -> Result<StepOutput, WorkflowError> {
    if event.score > 0.5 {
        Ok(StepOutput::Single(Box::new(PositiveEvent { text: event.text })))
    } else {
        Ok(StepOutput::Single(Box::new(NegativeEvent { text: event.text })))
    }
}