Wildcard Subscription

Overview

A wildcard subscription lets one subscriber match a whole family of channels with a single call, instead of wiring up a separate subscribe_to_events for every sub-channel and touching code each time a new one appears. It's the natural fit for monitoring, logging, or fan-in aggregation across a channel hierarchy — for example, watching every regional order channel from one place.

KubeMQ matches wildcard tokens against the channel hierarchy server-side at delivery time. * matches exactly one dot-separated segment, and > matches one or more trailing segments, so client.subscribe_to_events("rust-events.wildcard.*", ...) catches any single-segment suffix. Every delivered event still carries its exact channel, so the callback can tell which concrete sub-channel it came from even though the subscription itself only named a pattern.

Gotchas: * matches exactly one segment — it won't reach two levels deep, so orders.* misses orders.us.east; use > for that. Wildcards are only valid on Events subscriptions, not on send_event/publishes or on events-store, queues, or commands/queries. And an overly broad pattern like > at the root will quietly pull in every channel under that prefix, including ones you didn't intend to monitor.

Prerequisites

• KubeMQ server running on localhost:50000
• Rust SDK installed (cargo add kubemq)

Code

use kubemq::prelude::*;
use kubemq::EventBuilder;
use std::time::Duration;

#[tokio::main]
async fn main() -> kubemq::Result<()> {
    let client = KubemqClient::builder()
        .host("localhost")
        .port(50000)
        .build()
        .await?;

    let sub = client
        .subscribe_to_events(
            "rust-events.wildcard.*",
            "",
            |event| {
                Box::pin(async move {
                    println!(
                        "Wildcard received: channel={}, body={}",
                        event.channel,
                        String::from_utf8_lossy(&event.body)
                    );
                })
            },
            None,
        )
        .await?;

    tokio::time::sleep(Duration::from_millis(500)).await;

    for suffix in &["orders", "users", "logs"] {
        let channel = format!("rust-events.wildcard.{}", suffix);
        let event = EventBuilder::new()
            .channel(&channel)
            .body(format!("message for {}", suffix).into_bytes())
            .build();
        client.send_event(event).await?;
        println!("Sent event to {}", channel);
    }

    tokio::time::sleep(Duration::from_secs(2)).await;
    sub.unsubscribe().await;
    client.close().await?;
    Ok(())
}

How It Works

• Wildcard patterns (*, >) are supported on subscriptions but not on sends.
• * matches a single segment; > matches one or more segments.
• Review timeouts, channel names, and client IDs before running against shared environments.
• Run the program while the server from the prerequisites is available.

Related

• Events overview
• Rust SDK Reference
• Basic Pub/Sub