main.go

package main

import (
	"encoding/json"
	"fmt"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/collectors"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"net/http"
)

var dvs []Device
var version string

type Device struct {
	ID       int    `json:"id"`
	Mac      string `json:"mac"`
	Firmware string `json:"firmware"`
}

type metrics struct {
	devices prometheus.Gauge
	info    *prometheus.GaugeVec
}

func main() {
	reg := prometheus.NewRegistry()
	reg.MustRegister(collectors.NewGoCollector())
	m := NewMetrics(reg)

	m.devices.Set(float64(len(dvs)))
	m.info.With(prometheus.Labels{"version": version}).Set(1)

	promHandler := promhttp.HandlerFor(reg, promhttp.HandlerOpts{Registry: reg})

	http.Handle("/metrics", promHandler)
	http.HandleFunc("/", HelloServer)
	http.HandleFunc("/devices", getDevices)
	err := http.ListenAndServe(":8081", nil)
	if err != nil {
		return
	}
}

func HelloServer(w http.ResponseWriter, r *http.Request) {
	_, err := fmt.Fprintf(w, "Hello, %sMetrics", r.URL.Path[1:])
	if err != nil {
		return
	}
}

func init() {
	version = "2.10.5"

	dvs = []Device{
		{1, "5F-33-CC-1F-43-82", "2.1.6"},
		{2, "EF-2B-C4-F5-D6-34", "2.1.6"},
	}
}

func getDevices(w http.ResponseWriter, r *http.Request) {
	b, err := json.Marshal(dvs)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	w.Write(b)
}

func NewMetrics(reg prometheus.Registerer) *metrics {
	m := &metrics{
		devices: prometheus.NewGauge(prometheus.GaugeOpts{
			Namespace: "myapp",
			Name:      "connected_devices",
			Help:      "Number of currently connected devices.",
		}),
		info: prometheus.NewGaugeVec(prometheus.GaugeOpts{
			Namespace: "myapp",
			Name:      "info",
			Help:      "Information about the My App environment.",
		}, []string{"version"}),
	}
	reg.MustRegister(m.devices, m.info)
	return m
}