Module trace 

W3C Trace Context (traceparent) propagation

A request that crosses several services is only debuggable when every service logs the same trace id. TraceLayer reads the incoming traceparent header (or starts a new trace), gives the request its own span, and makes the ids available to handlers, the access log and outgoing calls:

use ullun::client::HttpClient;
use ullun::prelude::*;
use ullun::trace::TraceLayer;

App::new()
    .middleware(TraceLayer::new())
    .get("/orders", |req: Request| async move {
        // the call below carries the same trace id; the callee's parent is this span
        let upstream = HttpClient::new()
            .get("http://inventory.internal/stock")
            .trace(&req)
            .send()
            .await?;
        Ok(Response::text(upstream.text()?))
    })
    .run("127.0.0.1:3000")
    .await
    .unwrap();

AccessLog adds trace=<id> (text) or trace_id (JSON) to its lines when the layer is installed. This is the propagation half of distributed tracing, without an exporter: ship the ids with your logs, or read Request::trace from your own OpenTelemetry glue. Facing the internet, use TraceLayer::ignore_incoming so callers cannot choose your trace ids.

Structs

TraceContext

Trace identity of the current request, stored in Request::extensions

TraceLayer

Middleware that continues or starts a W3C trace