add chi metrics middleware.

internal/api/router.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"net/http"
 
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+
 	"gitlab.com/demodesk/neko/server/internal/api/members"
 	"gitlab.com/demodesk/neko/server/internal/api/room"
 	"gitlab.com/demodesk/neko/server/pkg/auth"
@@ -62,6 +64,11 @@ func (api *ApiManagerCtx) Route(r types.Router) {
 		_, err := w.Write([]byte("true"))
 		return err
 	})
+
+	r.Get("/metrics", func(w http.ResponseWriter, r *http.Request) error {
+		promhttp.Handler().ServeHTTP(w, r)
+		return nil
+	})
 }
 
 func (api *ApiManagerCtx) Authenticate(w http.ResponseWriter, r *http.Request) (context.Context, error) {

internal/http/metrics.go

@@ -0,0 +1,57 @@
+package http
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/go-chi/chi/middleware"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Middleware is a handler that exposes prometheus metrics for the number of requests,
+// the latency and the response size, partitioned by status code, method and HTTP path.
+type metrics struct {
+	reqs    *prometheus.CounterVec
+	latency *prometheus.HistogramVec
+}
+
+// NewMiddleware returns a new prometheus Middleware handler.
+func middlewareMetrics(next http.Handler) http.Handler {
+	var m metrics
+
+	m.reqs = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name:      "requests_total",
+			Namespace: "neko",
+			Subsystem: "http",
+			Help:      "How many HTTP requests processed, partitioned by status code, method and HTTP path.",
+		},
+		[]string{"code", "method", "path"},
+	)
+	prometheus.MustRegister(m.reqs)
+
+	m.latency = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:      "request_duration_milliseconds",
+		Namespace: "neko",
+		Subsystem: "http",
+		Help:      "How long it took to process the request, partitioned by status code, method and HTTP path.",
+		Buckets:   []float64{300, 1200, 5000},
+	},
+		[]string{"code", "method", "path"},
+	)
+
+	prometheus.MustRegister(m.latency)
+	return m.handler(next)
+}
+
+func (c metrics) handler(next http.Handler) http.Handler {
+	fn := func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+		next.ServeHTTP(ww, r)
+		c.reqs.WithLabelValues(http.StatusText(ww.Status()), r.Method, r.URL.Path).Inc()
+		c.latency.WithLabelValues(http.StatusText(ww.Status()), r.Method, r.URL.Path).Observe(float64(time.Since(start).Nanoseconds()) / 1000000)
+	}
+
+	return http.HandlerFunc(fn)
+}

internal/http/router.go

@@ -20,6 +20,7 @@ func newRouter(logger zerolog.Logger) *router {
 	r := chi.NewRouter()
 	r.Use(middleware.RequestID) // Create a request ID for each request
 	r.Use(middleware.RequestLogger(&logFormatter{logger}))
+	r.Use(middlewareMetrics)
 	r.Use(middleware.Recoverer) // Recover from panics without crashing server
 	return &router{r}
 }