From 87e1be84a219cdfabd7d13aa98d7fd66b0d05704 Mon Sep 17 00:00:00 2001
From: msi
Date: Thu, 13 Nov 2025 16:42:07 -0300
Subject: Add prometheus metrics

---
 web/template/src/metric.rs | 103 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 web/template/src/metric.rs

(limited to 'web/template/src/metric.rs')

diff --git a/web/template/src/metric.rs b/web/template/src/metric.rs
new file mode 100644
index 0000000..91a26cc
--- /dev/null
+++ b/web/template/src/metric.rs
@@ -0,0 +1,103 @@
+//
+// Copyright (c) 2025 murilo ijanc' <murilo@ijanc.org>
+//
+// Permission to use, copy, modify, and distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+use std::{
+    future::ready,
+    time::{Duration, Instant},
+};
+
+use axum::{
+    Router,
+    extract::{MatchedPath, Request},
+    middleware::Next,
+    response::IntoResponse,
+    routing::get,
+};
+use metrics_exporter_prometheus::{
+    Matcher, PrometheusBuilder, PrometheusHandle,
+};
+
+use crate::helpers;
+
+pub(crate) async fn start_metrics_server() -> anyhow::Result<()> {
+    let app = metrics_app();
+
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:3001").await?;
+    tracing::info!("metrics listening on {}", listener.local_addr()?);
+    axum::serve(listener, app)
+        .with_graceful_shutdown(helpers::shutdown_signal())
+        .await?;
+
+    Ok(())
+}
+
+fn metrics_app() -> Router {
+    let recorder_handle = setup_metrics_recorder();
+    Router::new()
+        .route("/metrics", get(move || ready(recorder_handle.render())))
+}
+
+fn setup_metrics_recorder() -> PrometheusHandle {
+    const EXPONENTIAL_SECONDS: &[f64] =
+        &[0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0];
+
+    let recorder_handle = PrometheusBuilder::new()
+        .set_buckets_for_metric(
+            Matcher::Full("http_requests_duration_seconds".to_string()),
+            EXPONENTIAL_SECONDS,
+        )
+        .unwrap()
+        .install_recorder()
+        .unwrap();
+
+    let upkeep_handle = recorder_handle.clone();
+    tokio::spawn(async move {
+        loop {
+            tokio::time::sleep(Duration::from_secs(5)).await;
+            upkeep_handle.run_upkeep();
+        }
+    });
+
+    recorder_handle
+}
+
+pub(crate) async fn track_metrics(
+    req: Request,
+    next: Next,
+) -> impl IntoResponse {
+    let start = Instant::now();
+    let path =
+        if let Some(matched_path) = req.extensions().get::<MatchedPath>() {
+            matched_path.as_str().to_owned()
+        } else {
+            req.uri().path().to_owned()
+        };
+    let method = req.method().clone();
+
+    let response = next.run(req).await;
+
+    let latency = start.elapsed().as_secs_f64();
+    let status = response.status().as_u16().to_string();
+
+    let labels =
+        [("method", method.to_string()), ("path", path), ("status", status)];
+
+    metrics::counter!("http_requests_total", &labels).increment(1);
+    metrics::histogram!("http_requests_duration_seconds", &labels)
+        .record(latency);
+
+    response
+}
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