Broadcast and RPC: talking to players

The server half decides; the client half shows. Neither can do the other’s job, so every piece of feedback a player sees is a message that crossed between them.

Server to client

broadcast::send(channel, payload).await;                 // everyone
broadcast::send_to(&player_id, channel, payload).await;  // one player

Both deliver to the client halves of the same mod on the receiving peers, as client-api::on-message(channel, data). The payload is bytes: pick your own encoding.

send-to is what makes per-player state possible — each player’s own score, their own countdown, “you are it”.

The receiving client half renders it:

async fn on_message(channel: String, data: Vec<u8>) {
    if channel != MY_CHANNEL { return; }
    ui::set_overlay_text(&format!("score: {}", decode(&data)));
}

set-overlay-text replaces one line of text. That is the entire presentation surface today.

Client to server

let reply = rpc_out::call(method, args).await?;   // client half only

The host routes the call to whichever loaded server mod claims that method in handle-rpc. A mod that does not own the method returns an error and the host keeps looking, so unrelated mods coexisting is fine — but two mods claiming one name is a race you should avoid by namespacing method names.

The pattern that avoids lying to yourself

echo, the one reference mod with both halves, ignores the value its own RPC returns and renders only what arrives over the broadcast. That is deliberate: if the caller trusted the return, a completely broken broadcast would still look correct on the screen of the person pressing the key — and only they would be right.

So: act on the broadcast, not the reply. The reply tells you the call succeeded; the broadcast tells you the world agrees.

The one available keypress

There is no input system for mods. Exactly one action reaches client halves — echo, sent on F — and every client mod sees it and must filter by name. You cannot register an action or bind a key (why).

For real interaction use trigger volumes and interact presses, which are proper mechanisms routed to the owning mod.