powerdns-remote-http-example/prometheus.go

package main

import (
	"log"
	"net/http"
	"strings"

	"github.com/gin-gonic/gin"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

// TODO: more metrics

var (
	_promRegistry    *prometheus.Registry
	_promHttpHandler http.Handler

	promOpsProcessed = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "processed_ops_total",
		Help: "The total number of processed requests",
	})

	promAddr4Count = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
		Name: "ipv4_mapped_addr_count",
		Help: "The total number of IPv4-mapped addresses",
	}, func() float64 {
		var x uint32
		addr4.Range(func(key, value any) bool {
			x++
			return true
		})
		return float64(x)
	})

	promAddr6Count = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
		Name: "ipv6_mapped_addr_count",
		Help: "The total number of IPv6-mapped addresses",
	}, func() float64 {
		var x uint32
		addr6.Range(func(key, value any) bool {
			x++
			return true
		})
		return float64(x)
	})

	labelStringReplacer *strings.Replacer = strings.NewReplacer(
		"\"", "",
		"'", "",
	)
)

func setupPrometheus(r *gin.Engine) {
	_promRegistry = prometheus.NewRegistry()
	_promRegistry.MustRegister(promOpsProcessed)
	_promRegistry.MustRegister(promAddr4Count)
	_promRegistry.MustRegister(promAddr6Count)

	_promHttpHandler = promhttp.HandlerFor(_promRegistry, promhttp.HandlerOpts{
		Registry:          _promRegistry,
		EnableOpenMetrics: true,
		ErrorHandling:     promhttp.ContinueOnError,
		ErrorLog:          log.Default(),
	})

	r.GET("/metrics", promHttpHandler)
	r.GET("/metrics/", func(c *gin.Context) {
		c.Redirect(http.StatusMovedPermanently, "/metrics")
	})
}

func promSanitizeLabel(str string, fallback string) string {
	out := strings.ToValidUTF8(str, "")
	out = labelStringReplacer.Replace(out)
	out = strings.TrimSpace(out)
	if out == "" {
		return fallback
	}
	return out
}

func promHttpHandler(c *gin.Context) {
	promOpsProcessed.Inc()

	_promHttpHandler.ServeHTTP(c.Writer, c.Request)
}