From e2dbe5e6c0b78a5f372ac2798e4ad7944f6a80a5 Mon Sep 17 00:00:00 2001
From: Anirudh Oppiliappan <anirudh@tangled.org>
Date: Mon, 11 May 2026 23:47:26 +0300
Subject: [PATCH] knotmirror/xrpc: add more prometheus metrics

Signed-off-by: Anirudh Oppiliappan <anirudh@tangled.org>
---
 knotmirror/xrpc/metrics.go | 59 ++++++++++++++++++++++++++++++++++++++
 knotmirror/xrpc/xrpc.go    |  1 +
 nix/modules/knotmirror.nix | 10 +++----
 3 files changed, 65 insertions(+), 5 deletions(-)
 create mode 100644 knotmirror/xrpc/metrics.go

diff --git a/knotmirror/xrpc/metrics.go b/knotmirror/xrpc/metrics.go
new file mode 100644
index 00000000..1618f340
--- /dev/null
+++ b/knotmirror/xrpc/metrics.go
@@ -0,0 +1,59 @@
+package xrpc
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	httpRequestsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "knotmirror_http_requests_total",
+		Help: "Total number of HTTP requests",
+	}, []string{"method", "path", "status", "repo"})
+
+	httpRequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "knotmirror_http_request_duration_seconds",
+		Help:    "HTTP request duration in seconds",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"method", "path", "status", "repo"})
+)
+
+type statusRecorder struct {
+	http.ResponseWriter
+	status int
+}
+
+func (r *statusRecorder) WriteHeader(status int) {
+	r.status = status
+	r.ResponseWriter.WriteHeader(status)
+}
+
+func metricsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
+		start := time.Now()
+
+		next.ServeHTTP(rec, r)
+
+		routePattern := chi.RouteContext(r.Context()).RoutePattern()
+		if routePattern == "" {
+			routePattern = "unknown"
+		}
+
+		repo := r.URL.Query().Get("repo")
+		if repo == "" {
+			repo = "unknown"
+		}
+
+		status := fmt.Sprintf("%d", rec.status)
+		duration := time.Since(start).Seconds()
+
+		httpRequestsTotal.WithLabelValues(r.Method, routePattern, status, repo).Inc()
+		httpRequestDuration.WithLabelValues(r.Method, routePattern, status, repo).Observe(duration)
+	})
+}
diff --git a/knotmirror/xrpc/xrpc.go b/knotmirror/xrpc/xrpc.go
index 9852e740..557fbb94 100644
--- a/knotmirror/xrpc/xrpc.go
+++ b/knotmirror/xrpc/xrpc.go
@@ -46,6 +46,7 @@ func New(logger *slog.Logger, cfg *config.Config, db *sql.DB, rdb *redis.Client,
 
 func (x *Xrpc) Router() http.Handler {
 	r := chi.NewRouter()
+	r.Use(metricsMiddleware)
 
 	r.Group(func(r chi.Router) {
 		r.Use(x.inflight.middleware)
diff --git a/nix/modules/knotmirror.nix b/nix/modules/knotmirror.nix
index 2759f88b..d981fd0a 100644
--- a/nix/modules/knotmirror.nix
+++ b/nix/modules/knotmirror.nix
@@ -30,16 +30,16 @@ in
         description = "Address to listen on";
       };
 
-      metricsListenAddr = mkOption {
+      adminListenAddr = mkOption {
         type = types.str;
-        default = "127.0.0.1:7100";
+        default = "127.0.0.1:7200";
         description = "Address to listen on";
       };
 
-      adminListenAddr = mkOption {
+      metricsListenAddr = mkOption {
         type = types.str;
-        default = "127.0.0.1:7200";
-        description = "Address to listen on";
+        default = "0.0.0.0:7100";
+        description = "Listen address for the Prometheus metrics endpoint";
       };
 
       hostname = mkOption {
-- 
2.51.2