Emit events

Task: announce that something changed so clients can react.

Declare the events

An #[app::event] enum in the #[app::logic] module. The variant name is the event name; the fields are its data (camelCase keys; u64, i64 and bytes as strings). From apps/kv-store:

#[app::event]
pub enum Event {
    /// A new key was stored.
    Inserted { key: String, value: String },
    /// An existing key's value was replaced.
    Updated { key: String, value: String },
    /// A key and its value were removed.
    Removed { key: String },
    /// Every key was removed from a non-empty store.
    Cleared,
}

The events and their fields are listed in the app’s ABI.

Emit them

pub fn update_if_exists(&mut self, key: String, value: String) -> app::Result<bool> {
    if !self.entries.contains(&key)? {
        return Ok(false);
    }
    self.entries.insert(&key, &value)?;
    env::emit(Event::Updated { key, value }, Audience::All)?;
    Ok(true)
}

env::emit(event, audience) adds the event to the run’s outcome. It reaches clients only if the call succeeds and its entry commits; a failed call emits nothing. env::emit_raw(name, &data, audience) emits any serde value by name.

Choose the audience

`Audience`	Receives it
`All`	Everyone subscribed to the app.
`Caller`	The caller of the run.
`Accounts(vec![..])`	These accounts.
`Team(id)`	The members of a team.
`Org`	The members of the app’s org.
`OrgAdmins`	The admins of the app’s org.

The node resolves the audience when it delivers, against the org at that moment.

Read them

Clients follow GET /apps/{app}/events?from=N: server-sent events, the committed events from log index N, then live ones (Node API). mero-js and calimero-client-py wrap the stream; meroctl context watch prints it.