Add tracing variable from middleware

[BenJeau]

Hi,

I'm extracting user information in a middleware and am using the TraceLayer, e.g. here is the router that I'm using

Router::new()
        .nest("/api/v1", app())
        .layer(TraceLayer::new_for_http())
        .route_layer(middleware::from_fn_with_state(
            app_state.clone(),
            middleware,
        ))

I'm unsure how to tackle this, I've tried the following, but it was not working correctly:

• Have the following in the middleware function (I think this is not working, since the guard gets dropped at the end of the function)

let span = span!(Level::ERROR, "user", username);
let _guard = span.enter();

I wouldn't mind adding it to the request trace from the TraceLayer

[jplatte]

You need to use .make_span_with on the TraceLayer to add the custom fields to the span (see this example), then use Span::current().record("field", value) in the middleware to set its value.

[BenJeau]

Thank you for the response! I've tried what you're suggesting and it does not seem to work, seems like the middleware gets called before the TraceLayer, e.g.

2023-01-20T13:08:44.836822Z  INFO rest_server::authentication::middleware: before adding user to request
2023-01-20T13:08:44.836913Z  INFO rest_server::authentication::middleware: after adding user to request
2023-01-20T13:08:44.839237Z  INFO rest_server::api: tracing layer

I found out that I need it to be like the following:

Router::new()
        .nest("/api/v1", app())
        .route_layer(middleware::from_fn_with_state(
            app_state.clone(),
            middleware,
        ))
        .layer(TraceLayer::new_for_http())

And If I do what you suggest, everything works, thank you :)

Now I see the following:

2023-01-20T13:52:33.764095Z  INFO request{method=GET uri=/enrichments version=HTTP/1.1}: rest_server::authentication::middleware: before adding user to request
2023-01-20T13:52:33.764151Z  INFO request{method=GET uri=/enrichments version=HTTP/1.1 username="admin"}: rest_server::authentication::middleware: after adding user to request

[davidpdrsn]

See https://docs.rs/axum/latest/axum/middleware/index.html#ordering for more info about middleware ordering.

[BenJeau]

Initially thought the ordering was the other way around - thanks for the docs