How do I get raw path params in a layer

[BLucky-gh]

Summary

I am trying to set up TraceLayer like this

        .layer(
            TraceLayer::new_for_http().make_span_with(|req: &Request<_>| {
                use axum::extract::{MatchedPath, RawPathParams};

                let matched_path = req
                    .extensions()
                    .get::<MatchedPath>()
                    .map(MatchedPath::as_str)
                    .unwrap_or(req.uri().path());

                let path_params = dbg!(req.extensions().get::<RawPathParams>()).map(|params| {
                    params
                        .into_iter()
                        .fold(HashMap::<&str, &str>::new(), |mut map, (k, v)| {
                            map.insert(k, v);
                            map
                        })
                });

                tracing::info_span!(
                    "http_request",
                    method = ?req.method(),
                    matched_path,
                    ?path_params
                )
            }),
        );

but path_params always returns None, even for a route that does have path params

for example the following handler

async fn path_params(Path(param): Path<String>, raw: RawPathParams) -> String {
    raw.into_iter().for_each(|x| debug!("{x:?}"));
    dbg!(param)
}

results in the following output

2025-02-05T09:57:47.537206Z TRACE axum::serve: connection 127.0.0.1:52183 accepted
[src/main.rs:104:35] req.extensions().get::<RawPathParams>() = None
2025-02-05T09:57:47.538939Z DEBUG http_request{method=GET matched_path="/path/{param}" path_params=None}: tower_http::trace::on_request: started processing request
2025-02-05T09:57:47.538979Z DEBUG http_request{method=GET matched_path="/path/{param}" path_params=None}: example_proj: ("param", "example")
[src/main.rs:141:5] param = "example"
2025-02-05T09:57:47.539041Z DEBUG http_request{method=GET matched_path="/path/{param}" path_params=None}: tower_http::trace::on_response: finished processing request latency=0 ms status=200

Showing that the RawPathParams extractor is indeed working, but it somehow doesn't work in the layer

axum version

0.8.1

[mladedav]

It usually isn't as straightforward to get an extracted parameter as just getting it as an extension.

You can look at the implementation to see how RawPathParams are actually constructed and use similar code.

You might also want to check from_fn_with_state.

[BLucky-gh]

I figured it would work since MatchedPath worked. Sadly the implementation doesn't really help me since it's getting UrlParams as an extension but UrlParams is private. I did end up finding out that I could do a RawPathParams::from_request, but 1) it's async, and make_span_with needs a sync closure and 2) I can't move out of the shared reference to req that I get in the closure

[mladedav]

Right, in that case I think you need to create the layer with from_fn which supports extractors and then I think that you can move the extracted paths to the closure for TraceLayer.