add basic axum metrics handler

Cargo.toml

@@ -7,6 +7,7 @@ members = [
     "crates/dscvr-canister-config",
     "crates/dscvr-canister-exports",
     "crates/dscvr-interface",
+    "crates/dscvr-telemetry-util",
     "crates/dscvr-tracing-util",
     "crates/ic-canister-io",
     "crates/ic-canister-logger",

crates/dscvr-telemetry-util/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "dscvr-telemetry-util"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+axum = "0.6"
+http = "0"
+metrics = "0"
+metrics-exporter-prometheus = "0"

crates/dscvr-telemetry-util/src/lib.rs

@@ -0,0 +1,30 @@
+use axum::{extract::MatchedPath, middleware::Next, response::Response};
+use http::Request;
+use std::time::Instant;
+
+pub async fn track_metrics<B>(req: Request<B>, next: Next<B>) -> Response {
+    let start = Instant::now();
+    let path = req
+        .extensions()
+        .get::<MatchedPath>()
+        .map(|path| path.as_str().to_owned());
+    let method = req.method().clone();
+
+    let response = next.run(req).await;
+
+    if let Some(path) = path {
+        let latency = start.elapsed().as_secs_f64();
+        let status = response.status().as_u16().to_string();
+
+        let labels = [
+            ("method", method.to_string()),
+            ("path", path.as_str().to_owned()),
+            ("status", status),
+        ];
+
+        metrics::counter!("rpc-request-count", &labels).increment(1);
+        metrics::histogram!("rpc-request-duration", &labels).record(latency);
+    }
+
+    response
+}