main.go

package main

import (
	"net/http"
	"strconv"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/go-chi/telemetry"
)

var AppMetrics = &MyAppMetrics{telemetry.NewScope("app")}

type MyAppMetrics struct {
	*telemetry.Scope
}

func (m *MyAppMetrics) RecordMyAppHit() {
	m.RecordHit("my_app_hit", nil)
}

func (m *MyAppMetrics) RecordAppGauge(value float64) {
	m.RecordGauge("my_app_gauge", nil, value)
}

func main() {
	r := chi.NewRouter()

	r.Use(middleware.Logger)

	// telemetry.Collector middleware mounts /metrics endpoint
	// with prometheus metrics collector.
	r.Use(telemetry.Collector(telemetry.Config{
		AllowAny: true,
	}, []string{"/api"})) // path prefix filters records generic http request metrics

	r.Route("/api", func(r chi.Router) {
		r.Get("/hello", func(w http.ResponseWriter, r *http.Request) {
			w.Write([]byte("Hello World!"))
		})
		r.Get("/hit", func(w http.ResponseWriter, r *http.Request) {
			// record a hit
			AppMetrics.RecordMyAppHit()
			w.Write([]byte("Hit recorded!"))
		})
		r.Get("/gauge/{value}", func(w http.ResponseWriter, r *http.Request) {
			value := chi.URLParam(r, "value")
			floatValue, err := strconv.ParseFloat(value, 64)
			if err != nil {
				w.Write([]byte("Invalid value"))
				return
			}
			// record a gauge
			AppMetrics.RecordAppGauge(floatValue)
			w.Write([]byte("Gauge recorded!"))
		})
	})

	http.ListenAndServe("localhost:3000", r)
}