feat: Add Prometheus metrics endpoint

src/api/client/unversioned.rs

@@ -1,9 +1,11 @@
 use axum::{Json, extract::State, response::IntoResponse};
 use conduwuit::{
-	Result,
+	Err, Result,
 	matrix::versions::{unstable_features, versions},
+	utils::string::constant_time_eq,
 };
 use futures::StreamExt;
+use http::{HeaderMap, header};
 use ruma::{api::client::discovery::get_supported_versions, assign};
 
 use crate::Ruma;
@@ -75,3 +77,37 @@ pub(crate) async fn continuwuity_local_user_count(
 		"count": user_count
 	})))
 }
+
+/// # `GET /_continuwuity/metrics`
+///
+/// Prometheus metrics in the OpenMetrics text format. Only routed when
+/// `allow_prometheus_metrics` is enabled.
+pub(crate) async fn continuwuity_metrics(
+	State(services): State<crate::State>,
+	headers: HeaderMap,
+) -> Result<impl IntoResponse> {
+	if let Some(token) = &services.config.prometheus_metrics_token {
+		let authorized = headers
+			.get(header::AUTHORIZATION)
+			.and_then(|value| value.to_str().ok())
+			.and_then(|value| value.split_once(' '))
+			.is_some_and(|(scheme, provided)| {
+				scheme.eq_ignore_ascii_case("bearer") && constant_time_eq(provided, token)
+			});
+
+		if !authorized {
+			return Err!(Request(Forbidden("Invalid metrics token")));
+		}
+	}
+
+	services.update_metrics()?;
+	let body = services.server.metrics.prometheus.encode()?;
+
+	Ok((
+		[(
+			header::CONTENT_TYPE,
+			"application/openmetrics-text; version=1.0.0; charset=utf-8",
+		)],
+		body,
+	))
+}