feat: otel axum spanner (#87)

prestwich · web-flow · commit e34c154738ec · 2025-10-22T13:47:04.000-04:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -4,7 +4,7 @@ name = "init4-bin-base"
 description = "Internal utilities for binaries produced by the init4 team"
 keywords = ["init4", "bin", "base"]
 
-version = "0.15.0"
+version = "0.15.1"
 edition = "2021"
 rust-version = "1.85"
 authors = ["init4", "James Prestwich", "evalir"]
@@ -30,6 +30,7 @@ tracing-subscriber = { version = "0.3.18", features = ["env-filter", "json", "re
 # OTLP
 opentelemetry_sdk = "0.30.0"
 opentelemetry = "0.30.0"
+opentelemetry-http = "0.30.0"
 opentelemetry-otlp = "0.30.0"
 opentelemetry-semantic-conventions = { version = "0.30.0", features = ["semconv_experimental"] }
 tracing-opentelemetry = "0.31.0"
@@ -47,12 +48,12 @@ oauth2 = { version = "5.0.0", optional = true }
 tokio = { version = "1.36.0", optional = true }
 
 # Other
-thiserror = "2.0.11"
+axum = "0.8.1"
 serde = { version = "1", features = ["derive"] }
+thiserror = "2.0.11"
+tower = "0.5.2"
 async-trait = { version = "0.1.80", optional = true }
 eyre = { version = "0.6.12", optional = true }
-axum = { version = "0.8.1", optional = true }
-tower = { version = "0.5.2", optional = true }
 
 # AWS
 aws-config = { version = "1.1.7", optional = true }
@@ -72,7 +73,7 @@ tokio = { version = "1.43.0", features = ["macros"] }
 default = ["alloy", "rustls"]
 alloy = ["dep:alloy"]
 aws = ["alloy", "alloy?/signer-aws", "dep:async-trait", "dep:aws-config", "dep:aws-sdk-kms"]
-perms = ["dep:oauth2", "dep:tokio", "dep:reqwest", "dep:signet-tx-cache", "dep:eyre", "dep:axum", "dep:tower"]
+perms = ["dep:oauth2", "dep:tokio", "dep:reqwest", "dep:signet-tx-cache", "dep:eyre"]
 rustls = ["dep:rustls", "rustls/aws-lc-rs"]
 
 [[example]]
diff --git a/src/lib.rs b/src/lib.rs
@@ -31,6 +31,9 @@ pub mod utils {
     /// Prometheus metrics utilities.
     pub mod metrics;
 
+    /// Axum OpenTelemetry utilities.
+    pub mod otel_axum;
+
     /// OpenTelemetry utilities.
     pub mod otlp;
 
diff --git a/src/utils/otel_axum.rs b/src/utils/otel_axum.rs
@@ -0,0 +1,69 @@
+use axum::extract::{MatchedPath, Request};
+use tower::{Layer, Service};
+use tracing::{info_span, instrument::Instrumented, Instrument};
+use tracing_opentelemetry::OpenTelemetrySpanExt;
+
+/// A [`Layer`] that adds OpenTelemetry spans to Axum requests.
+#[derive(Debug, Clone, Copy)]
+pub struct OtelAxumSpanLayer;
+
+/// A simple service
+#[derive(Debug, Clone)]
+pub struct OtelAxumSpanner<S> {
+    inner: S,
+}
+
+impl<S> Layer<S> for OtelAxumSpanLayer {
+    type Service = OtelAxumSpanner<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        OtelAxumSpanner { inner }
+    }
+}
+
+impl<S, Body> Service<Request<Body>> for OtelAxumSpanner<S>
+where
+    S: Service<Request<Body>>,
+{
+    type Response = S::Response;
+    type Error = S::Error;
+    type Future = Instrumented<S::Future>;
+
+    fn poll_ready(
+        &mut self,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        self.inner.poll_ready(cx)
+    }
+
+    fn call(&mut self, req: Request<Body>) -> Self::Future {
+        let parent_context = opentelemetry::global::get_text_map_propagator(|propagator| {
+            propagator.extract(&opentelemetry_http::HeaderExtractor(req.headers()))
+        });
+
+        let method = req.method().to_string();
+        let uri = req.uri().clone();
+        let route = req
+            .extensions()
+            .get::<MatchedPath>()
+            .map(|r| r.as_str())
+            .unwrap_or_else(|| uri.path());
+        let name = format!("{method} {route}");
+        let name = name.trim();
+
+        let span = info_span!(
+            "Http Request",
+            "otel.name" = name,
+            "otel.target" = name,
+            "otel.kind" = "server",
+            "http.request.method" = method,
+            "url.path" = uri.path(),
+            "url.scheme" = uri.scheme_str().unwrap_or(""),
+            "http.route" = route,
+            "http.response.status_code" = tracing::field::Empty,
+        );
+        span.set_parent(parent_context);
+
+        self.inner.call(req).instrument(span)
+    }
+}
