How do I use Router::or with TraceLayer?

[RabidFire]

Hello! I'm trying to use Router::or but running into an issue. I want to separate my /health check route so that it doesn't get the TraceLayer applied to it.

let api_router = Router::new()
    .route("/graphql", post(graphql_handler))
    .layer(TraceLayer::new_for_http());

let health_router = Router::new().route("/health", get(health_handler));

let app = api_router.or(health_router);

axum_server::bind("0.0.0.0:8080").serve(app).await.unwrap()

But I get this weird error:

|     axum_server::bind("0.0.0.0:8080").serve(app).await.unwrap()
|                                       ^^^^^ expected struct `ResponseBody`, found struct `http_body::combinators::box_body::BoxBody`

Thought I followed the documentation pretty closely, but I'm not able to get past this. Works if I remove the TraceLayer. Works if I use either api_router or health_router separately. Would appreciate any help!

[davidpdrsn]

The issue here is that Trace (applied by TraceLayer) changes the response body type. By default axum's response body type is axum::body::BoxBody but Trace changes that to tower_http::trace::ResponseBody. It does this because it needs to know when the body as been fully sent. You can see that in its Service implementation.

So the two routers don't have the same response body type meaning they cannot be combined. The solution is to call .boxed() on the one with the TraceLayer so .layer(TraceLayer::new_for_http()).boxed(). That changes the response body type so they now both match.

Here is a full example:

use axum::{
    handler::get,
    Router,
};
use std::net::SocketAddr;
use tower_http::trace::TraceLayer;

#[tokio::main]
async fn main() {
    let api_router = Router::new()
        .route("/graphql", get(|| async {}))
        .layer(TraceLayer::new_for_http())
        .boxed();

    let health_router = Router::new().route("/health", get(|| async {}));

    let app = api_router.or(health_router);

    // run it
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    tracing::debug!("listening on {}", addr);
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}