Server function breaks  tracing'span parenting (issue with axum-tracing-opentelemetry?)

**Problem**

I try to set up tracing + opentelemetry on the server (fullstack web), using axum-tracing-opentelemetry.
- Instrumenting the server function generates 2 unrelated traces (no parenting between the span of the handler and the span of the function)
- Instrumenting directly an axum handler generates 1 trace as expected

The "root"/parent span is created in the middleware.

**Steps To Reproduce**

Steps to reproduce the behavior:

Sorry for the long code listing

- Create a project with OpenTelemetry enabled on the server
- Add 2 endpoints
  - a server function `get_200()`
  - an axum route + handler for `get_200_direct()`
- `#[tracing::instrument]` both function

The code below should reproduce the case:

```toml
[dependencies]
anyhow = { version = "*", optional = true } # same version as dioxus
axum-tracing-opentelemetry = { version = "0.32", optional = true }
dioxus = { version = "0.7", features = ["router", "fullstack"] }
init-tracing-opentelemetry = { version = "0.33", features = [
  "tracing_subscriber_ext",
], optional = true }
serde_json = "*"
tokio = { version = "*", features = [
  "full",
], optional = true } # same version as dioxus
tower = { version = "0.5", features = ["util"], optional = true }
tower-http = { version = "0.6", features = [
  "compression-full",
  "cors",
  "decompression-full",
  "sensitive-headers",
  "timeout",
  "trace",
  "validate-request",
], optional = true }
tracing = { version = "*", optional = true } # same version as dioxus
tracing-opentelemetry-instrumentation-sdk = { version = "0.32", optional = true }

[dev-dependencies]
pretty_assertions = "1"
rstest = "0.26"

[features]
default = ["web", "server"]
# The feature that are only required for the web = ["dioxus/web"] build target should be optional and only enabled in the web = ["dioxus/web"] feature
web = ["dioxus/web"]
# # The feature that are only required for the desktop = ["dioxus/desktop"] build target should be optional and only enabled in the desktop = ["dioxus/desktop"] feature
# desktop = ["dioxus/desktop"]
# # The feature that are only required for the mobile = ["dioxus/mobile"] build target should be optional and only enabled in the mobile = ["dioxus/mobile"] feature
# mobile = ["dioxus/mobile"]
# The feature that are only required for the server = ["dioxus/server"] build target should be optional and only enabled in the server = ["dioxus/server"] feature
server = [
  "dioxus/server",
  "dep:anyhow",
  "dep:axum-tracing-opentelemetry",
  "dep:init-tracing-opentelemetry",
  "dep:tokio",
  "dep:tower",
  "dep:tower-http",
  "dep:tracing",
  "dep:tracing-opentelemetry-instrumentation-sdk",
]
```

```rust
use dioxus::prelude::*;

#[derive(Debug, Clone, Routable, PartialEq)]
#[rustfmt::skip]
enum Route {
    #[route("/")]
    Home,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Run `serve()` on the server only
    #[cfg(feature = "server")]
    main_server::launch(App)?;

    // When not on the server, just run `launch()` like normal
    #[cfg(not(feature = "server"))]
    dioxus::launch(App);

    Ok(())
}

#[component]
pub(crate) fn App() -> Element {
    rsx! {
        Router::<Route> {}
    }
}

#[component]
pub(crate) fn Home() -> Element {
    rsx! {
        "hello"
    }
}

#[cfg(feature = "server")]
mod main_server {
    use anyhow::Result;
    use axum_tracing_opentelemetry::middleware::{OtelAxumLayer, OtelInResponseLayer};
    use dioxus::fullstack::response::IntoResponse;
    use dioxus::fullstack::Json;
    use dioxus::prelude::*;
    use dioxus::server::axum::{routing::get, Router};
    use tokio::runtime;

    //TODO initialize tracing and other logging here
    //TODO move "/healthz" "/readyz" "/metrics" into an other port
    pub(crate) fn launch(app: fn() -> Element) -> Result<()> {
        // duplicate code of dioxus::serve because exporter of opentelemetry need a reactor
        // else "there is no reactor running, must be called from the context of a Tokio 1.x runtime"
        // a mutli-thread scheduler
        let rt = runtime::Runtime::new()?;

        // tracing's subscriber (logging) should be set before dioxus try to initialiaze logging
        let _guard = rt.block_on(async {
            init_tracing_opentelemetry::TracingConfig::production()
                .with_stderr() // to avoid mixing with dioxus accesslog like (on stdout)
                .init_subscriber()
        })?;
        // `dioxus::serve` can not be called insode a Runtime::block_on
        // "Cannot start a runtime from within a runtime. This happens because a function (like `block_on`) attempted to block the current thread while the thread is being used to drive asynchronous tasks"
        dioxus::serve(|| async move { new_router(app) })
        //unreachable!("Serving a fullstack app should never return")
    }

    fn new_router(app: fn() -> Element) -> Result<Router> {
        let router = dioxus::server::router(app)
            .route("/api/200-direct", get(get_200_direct))
            .layer((
                OtelAxumLayer::default().filter(|path| path.starts_with("/api")),
                OtelInResponseLayer,
            ));
        Ok(router)
    }

    #[get("/api/200")]
    #[tracing::instrument]
    pub(crate) async fn get_200() -> Result<Option<String>, HttpError> {
        use tracing_opentelemetry_instrumentation_sdk::find_current_trace_id;
        let trace_id = find_current_trace_id();
        sleep_10ms().await;
        Ok(trace_id)
    }

    #[tracing::instrument]
    pub(crate) async fn get_200_direct() -> impl IntoResponse {
        use tracing_opentelemetry_instrumentation_sdk::find_current_trace_id;
        let trace_id = find_current_trace_id();
        sleep_10ms().await;
        Json(serde_json::json!(trace_id))
    }

    #[tracing::instrument]
    async fn sleep_10ms() {
        tokio::time::sleep(std::time::Duration::from_millis(10)).await;
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use dioxus::server::axum::{
            body::{to_bytes, Body},
            http::{header::*, Request, StatusCode},
        };
        use pretty_assertions::assert_eq;
        use rstest::*;
        use tower::ServiceExt; // for `oneshot`

        #[rstest]
        #[case("/api/200-direct")]
        #[case("/api/200")]
        #[tokio::test(flavor = "multi_thread")]
        async fn test_header_tracing(#[case] uri: &str) {
            let _guard = init_tracing_opentelemetry::TracingConfig::development()
                .with_global_subscriber(true)
                .with_compact_format()
                .with_log_directives("warn")
                .init_subscriber()
                .unwrap();
            let app = new_router(crate::App).unwrap();
            let response = app
                .oneshot(Request::builder().uri(uri).body(Body::empty()).unwrap())
                .await
                .unwrap();
            let headers = response.headers().clone();
            dbg!(&headers);
            assert_eq!(response.status(), StatusCode::OK);
            assert_eq!(headers.get(CONTENT_TYPE).unwrap(), "application/json");
            //FIXME
            let body = to_bytes(response.into_body(), 64).await.unwrap();
            let body = String::from_utf8(body.to_vec()).unwrap();
            assert_eq!(
                &headers.get("traceparent").unwrap().to_str().unwrap()[3..35],
                &body[1..33]
            );
        }
    }
}
```

- launch test

```
❯ mise run //server:test
[//server:test] $ mkdir -p target/debug/deps/public
[//server:test] $ cargo nextest run --all-features --workspace
   Compiling cdviz-saas v0.2.1 (/mnt/nvme0n1p1/david/src/github.com/cdviz-dev/cdviz-saas/server)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 1.71s
────────────
 Nextest run ID 68c51663-62f8-478c-85d8-4c99417c8ca6 with nextest profile: default
    Starting 2 tests across 1 binary
        PASS [   0.031s] cdviz-saas::bin/cdviz-saas main_server::tests::test_header_tracing::case_1
        FAIL [   0.033s] cdviz-saas::bin/cdviz-saas main_server::tests::test_header_tracing::case_2
  stdout ───

    running 1 test
    test main_server::tests::test_header_tracing::case_2 ... FAILED

    failures:

    failures:
        main_server::tests::test_header_tracing::case_2

    test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.03s

  stderr ───
       0.000146885s  WARN main_server::tests::test_header_tracing::case_2 dioxus_server::config:66: No index.html found in public directory, using default index.html
       0.002113288s TRACE main_server::tests::test_header_tracing::case_2 HTTP request: otel::tracing:15: new http.request.method=GET network.protocol.version=1.1 server.address="" user_agent.original="" url.path="/api/200" url.scheme="" otel.name=GET otel.kind=Server span.type=web
       0.015495455s TRACE main_server::tests::test_header_tracing::case_2 HTTP request: otel::tracing:15: close time.busy=319µs time.idle=13.1ms http.request.method=GET network.protocol.version=1.1 server.address="" user_agent.original="" url.path="/api/200" url.scheme="" otel.name=GET otel.kind=Server span.type=web http.route="/api/200" otel.name="GET /api/200" http.response.status_code=200
    [src/main.rs:125:13] &headers = {
        "content-type": "application/json",
        "traceparent": "00-c8e5cdbd12fefc7f65cb47bc7f933a16-bb7ff2d11fea3446-01",
        "tracestate": "",
        "content-length": "4",
    }

    thread 'main_server::tests::test_header_tracing::case_2' (159922) panicked at src/main.rs:133:22:
    byte index 33 is out of bounds of `null`
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

  Cancelling due to test failure:
────────────
     Summary [   0.035s] 2 tests run: 1 passed, 1 failed, 0 skipped
        FAIL [   0.033s] cdviz-saas::bin/cdviz-saas main_server::tests::test_header_tracing::case_2
error: test run failed
[//server:test] ERROR task failed
```

Or Launch the server `dx serve`

Call the server function (Failed mismatch between trace_id (in header, second part of traceparent, and body)

```
❯ curl -i http://127.0.0.1:8080/api/200
HTTP/1.1 200 OK
content-type: application/json
traceparent: 00-716593b9cca26cba621caca4fd0c9b27-8ef08e999afbab13-01
tracestate:
content-length: 34
date: Mon, 03 Nov 2025 15:11:17 GMT
vary: origin, access-control-request-method, access-control-request-headers
access-control-allow-origin: *

"4b39265aa38511b6aa22b5e67cd68b80"
```

Call the direct axum handler (match of trace_id)
```
❯ curl -i http://127.0.0.1:8080/api/200-direct
HTTP/1.1 200 OK
content-type: application/json
traceparent: 00-ae6c2cf564ca9695dc11754e58f74ac5-ab343a0cc008cfc7-01
tracestate:
content-length: 34
date: Mon, 03 Nov 2025 15:11:49 GMT
vary: origin, access-control-request-method, access-control-request-headers
access-control-allow-origin: *

"ae6c2cf564ca9695dc11754e58f74ac5"
```

<img width="1281" height="469" alt="Image" src="https://github.com/user-attachments/assets/7bf2cf1a-4bee-4827-a672-f6ae0e41c015" />

**Expected behavior**


Same behavior (tracing span, parenting) between a server function and axum direct handler:
- no break in the parenting, 
- only one trace_id

**Environment:**

- Dioxus version:  0.7.0
- Rust version:    1.91.0
- OS info:         Linux 6.12.48-1-MANJARO
- App platform:    web

**Questionnaire**



I'm interested in fixing this myself but don't know where to start.


I'm the maintainer of axum-tracing-opentelemetry, so I can update it if requested.

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Server function breaks tracing'span parenting (issue with axum-tracing-opentelemetry?) #4896

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Server function breaks tracing'span parenting (issue with axum-tracing-opentelemetry?) #4896

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