feat: prometheus metrics

internal/middleware/prometheus.go

@@ -0,0 +1,58 @@
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	httpRequestsTotal = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "http_requests_total",
+			Help: "Total number of HTTP requests",
+		},
+		[]string{"method", "path", "status"},
+	)
+
+	httpRequestDuration = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "http_request_duration_seconds",
+			Help:    "Duration of HTTP requests",
+			Buckets: prometheus.DefBuckets,
+		},
+		[]string{"method", "path", "status"},
+	)
+)
+
+func init() {
+	prometheus.MustRegister(httpRequestsTotal, httpRequestDuration)
+}
+
+func PrometheusMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		rr := &responseRecorder{ResponseWriter: w, statusCode: 200}
+		next.ServeHTTP(rr, r)
+		duration := time.Since(start)
+
+		method := r.Method
+		path := r.URL.Path
+		status := strconv.Itoa(rr.statusCode)
+
+		httpRequestsTotal.WithLabelValues(method, path, status).Inc()
+		httpRequestDuration.WithLabelValues(method, path, status).Observe(duration.Seconds())
+	})
+}
+
+type responseRecorder struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (rr *responseRecorder) WriteHeader(code int) {
+	rr.statusCode = code
+	rr.ResponseWriter.WriteHeader(code)
+}

internal/server/router.go

@@ -11,8 +11,10 @@ import (
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/go-chi/cors"
 	"github.com/go-chi/httprate"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 
 	"api/internal/handler"
+	app_middleware "api/internal/middleware"
 )
 
 func getAllowedOrigins() []string {
@@ -29,6 +31,7 @@ func NewRouter() {
 	r := chi.NewRouter()
 
 	// Middleware
+	r.Use(app_middleware.PrometheusMiddleware)
 	r.Use(middleware.RequestID)
 	r.Use(middleware.RealIP)
 	r.Use(middleware.Logger)
@@ -43,6 +46,9 @@ func NewRouter() {
 		MaxAge:         300,
 	}))
 
+	// Prometheus
+	r.Handle("/metrics", promhttp.Handler())
+
 	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		json.NewEncoder(w).Encode(map[string]string{