go-example/hello/metrics.go

package hello

import (
	"net/http"
	"strconv"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

var (
	httpRequestsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "http_requests_total",
		Help: "Total number of HTTP requests.",
	}, []string{"path", "method", "status"})

	httpRequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "http_request_duration_seconds",
		Help:    "Duration of HTTP requests.",
		Buckets: prometheus.DefBuckets,
	}, []string{"path", "method", "status"})
)

// Middleware wraps an http.HandlerFunc with Prometheus metrics
func Middleware(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		ww := &responseWriter{ResponseWriter: w, status: http.StatusOK}

		next(ww, r)

		duration := time.Since(start).Seconds()
		status := strconv.Itoa(ww.status)
		path := r.URL.Path
		method := r.Method

		httpRequestsTotal.WithLabelValues(path, method, status).Inc()
		httpRequestDuration.WithLabelValues(path, method, status).Observe(duration)
	}
}

type responseWriter struct {
	http.ResponseWriter
	status int
}

func (rw *responseWriter) WriteHeader(code int) {
	rw.status = code
	rw.ResponseWriter.WriteHeader(code)
}