Tracing Broadcast

A tracing_subscriber::Layer that fans every emitted event into a tokio::sync::broadcast channel as a serializable [TracingFrame] (timestamp / level / target / message / structured fields).

Features

Useful for any service that wants to expose a "tail my logs" stream over a management API, RPC, or websocket — BroadcastTracingLayer plugs alongside the normal tracing_subscriber::fmt::Layer, so user- visible logging on stderr stays unchanged. Each subscriber gets its own broadcast::Receiver with independent backlog tracking; slow subscribers see RecvError::Lagged(n) and resume from the next available frame.

Example

use tracing_broadcast::BroadcastTracingLayer;
use tracing_subscriber::layer::SubscriberExt;
use tracing_subscriber::util::SubscriberInitExt;

# async fn run() {
let layer = BroadcastTracingLayer::new();
let mut rx = layer.subscribe();

let _guard = tracing_subscriber::registry().with(layer.clone()).set_default();
tracing::info!(addr = "127.0.0.1", port = 8080_u64, "listener bound");

let frame = rx.recv().await.unwrap();
assert_eq!(frame.level, "INFO");
assert_eq!(frame.message, "listener bound");
assert_eq!(frame.fields["port"], 8080);
# }

TracingFrame derives serde::Serialize / Deserialize, so the operator-facing transport (NDJSON, websocket text frames, etc.) is just serde_json::to_string(&frame).

License

Released under the MIT License © 2026 Canmi