From bde3d57fdd1a1916099187877d2fe22e24f3b6f2 Mon Sep 17 00:00:00 2001
From: Martin Saporiti <martinsaporiti@gmail.com>
Date: Fri, 5 Apr 2024 12:36:22 -0300
Subject: [PATCH] chore: add prometheus metrics

---
 cmd/main.go                 | 13 ++++++-
 internal/api/metrics.go     | 11 ++++++
 internal/metrics/metrics.go | 76 +++++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 internal/api/metrics.go
 create mode 100644 internal/metrics/metrics.go

diff --git a/cmd/main.go b/cmd/main.go
index 6430866..7bac7d7 100644
--- a/cmd/main.go
+++ b/cmd/main.go
@@ -11,14 +11,18 @@ import (
 	chiMiddleware "github.com/go-chi/chi/v5/middleware"
 	"github.com/go-chi/cors"
 	"github.com/iden3/go-iden3-auth/v2/loaders"
+	"github.com/prometheus/client_golang/prometheus"
 	log "github.com/sirupsen/logrus"
 
 	"github.com/0xPolygonID/verifier-backend/internal/api"
 	"github.com/0xPolygonID/verifier-backend/internal/config"
 	"github.com/0xPolygonID/verifier-backend/internal/errors"
+	"github.com/0xPolygonID/verifier-backend/internal/metrics"
 )
 
 func main() {
+	registerMetrics()
+
 	cfg, err := config.Load()
 	if err != nil {
 		log.WithField("error", err).Error("cannot load config")
@@ -28,8 +32,8 @@ func main() {
 	keysLoader := &loaders.FSKeyLoader{Dir: cfg.KeyDIR}
 
 	mux := chi.NewRouter()
-
 	mux.Use(
+		metrics.PrometheusTotalRequestsMiddleware,
 		chiMiddleware.RequestID,
 		chiMiddleware.Recoverer,
 		cors.Handler(cors.Options{AllowedOrigins: []string{"*"}}),
@@ -40,6 +44,7 @@ func main() {
 	api.HandlerFromMux(api.NewStrictHandlerWithOptions(apiServer, nil,
 		api.StrictHTTPServerOptions{RequestErrorHandlerFunc: errors.RequestErrorHandlerFunc}), mux)
 	api.RegisterStatic(mux)
+	api.RegisterMetrics(mux)
 
 	server := &http.Server{
 		Addr:    fmt.Sprintf(":%s", cfg.ApiPort),
@@ -58,3 +63,9 @@ func main() {
 	<-quit
 	log.Info("Shutting down")
 }
+
+func registerMetrics() {
+	prometheus.MustRegister(metrics.TotalRequests)
+	prometheus.MustRegister(metrics.HttpDuration)
+	prometheus.MustRegister(metrics.ResponseStatus)
+}
diff --git a/internal/api/metrics.go b/internal/api/metrics.go
new file mode 100644
index 0000000..c2ad6f1
--- /dev/null
+++ b/internal/api/metrics.go
@@ -0,0 +1,11 @@
+package api
+
+import (
+	"github.com/go-chi/chi/v5"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// RegisterMetrics -  registers the static routes for the API.
+func RegisterMetrics(mux *chi.Mux) {
+	mux.Handle("/metrics", promhttp.Handler())
+}
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
new file mode 100644
index 0000000..d2379da
--- /dev/null
+++ b/internal/metrics/metrics.go
@@ -0,0 +1,76 @@
+package metrics
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// TotalRequests - CounterVec to store the total number of requests per path
+var TotalRequests = prometheus.NewCounterVec(
+	prometheus.CounterOpts{
+		Name: "http_requests_total_per_path",
+		Help: "Number of get requests per path",
+	},
+	[]string{"path"},
+)
+
+// ResponseStatus - CounterVec to store the status of the response
+var ResponseStatus = prometheus.NewCounterVec(
+	prometheus.CounterOpts{
+		Name: "http_response_status",
+		Help: "Status of HTTP response",
+	},
+	[]string{"status"},
+)
+
+// HttpDuration - HistogramVec to store the duration of the HTTP requests per path
+var HttpDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+	Name: "http_response_time_seconds_per_path",
+	Help: "Duration of HTTP requests per path",
+}, []string{"path"})
+
+type responseWriter struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func newResponseWriter(w http.ResponseWriter) *responseWriter {
+	return &responseWriter{w, http.StatusOK}
+}
+
+func (rw *responseWriter) WriteHeader(code int) {
+	rw.statusCode = code
+	rw.ResponseWriter.WriteHeader(code)
+}
+
+// PrometheusTotalRequestsMiddleware - Middleware to record metrics for the API
+func PrometheusTotalRequestsMiddleware(next http.Handler) http.Handler {
+	fn := func(w http.ResponseWriter, r *http.Request) {
+		ctx := r.Context()
+		path := r.URL.Path
+		if mustBeExcluded(path) {
+			next.ServeHTTP(w, r.WithContext(ctx))
+			return
+		}
+		timer := prometheus.NewTimer(HttpDuration.WithLabelValues(path))
+		rw := newResponseWriter(w)
+		next.ServeHTTP(rw, r)
+
+		statusCode := rw.statusCode
+		ResponseStatus.WithLabelValues(strconv.Itoa(statusCode)).Inc()
+		TotalRequests.WithLabelValues(path).Inc()
+
+		timer.ObserveDuration()
+	}
+	return http.HandlerFunc(fn)
+}
+
+func mustBeExcluded(path string) bool {
+	mustBe := false
+	if path == "" || path == "/static/docs/api/api.yaml" || path == "/metrics" {
+		mustBe = true
+	}
+	return mustBe
+}