initial checkin

2026-03-24 20:30:16 +01:00
commit edc8f4296a
6 changed files with 414 additions and 0 deletions
--- a/main.go
+++ b/main.go
@@ -0,0 +1,136 @@
+package main
+
+import (
+	"encoding/csv"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"math/rand"
+	"net/http"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+
+type exporter struct {
+	mu      sync.RWMutex
+	uptime  *prometheus.GaugeVec
+	fetchOk prometheus.Gauge
+	fetchAt prometheus.Gauge
+}
+
+func newExporter(reg prometheus.Registerer) *exporter {
+	e := &exporter{
+		uptime: prometheus.NewGaugeVec(prometheus.GaugeOpts{
+			Name: "ct_log_uptime_ratio",
+			Help: "24h uptime ratio (0–1) for a CT log endpoint, sourced from gstatic.com.",
+		}, []string{"log_url", "endpoint"}),
+		fetchOk: prometheus.NewGauge(prometheus.GaugeOpts{
+			Name: "ct_log_uptime_fetch_success",
+			Help: "1 if the last CSV fetch succeeded, 0 otherwise.",
+		}),
+		fetchAt: prometheus.NewGauge(prometheus.GaugeOpts{
+			Name: "ct_log_uptime_fetch_timestamp_seconds",
+			Help: "Unix timestamp of the last CSV fetch attempt.",
+		}),
+	}
+	reg.MustRegister(e.uptime, e.fetchOk, e.fetchAt)
+	return e
+}
+
+func (e *exporter) fetch(csvURL string) error {
+	resp, err := http.Get(csvURL)
+	if err != nil {
+		return fmt.Errorf("GET %s: %w", csvURL, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unexpected status %s", resp.Status)
+	}
+
+	r := csv.NewReader(resp.Body)
+	// skip header
+	if _, err := r.Read(); err != nil {
+		return fmt.Errorf("read header: %w", err)
+	}
+
+	// collect new values before updating metrics
+	type row struct{ logURL, endpoint string; ratio float64 }
+	var rows []row
+	for {
+		rec, err := r.Read()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("read row: %w", err)
+		}
+		if len(rec) < 3 {
+			continue
+		}
+		pct, err := strconv.ParseFloat(rec[2], 64)
+		if err != nil {
+			log.Printf("skipping row with unparseable uptime %q: %v", rec[2], err)
+			continue
+		}
+		rows = append(rows, row{rec[0], rec[1], pct / 100.0})
+	}
+
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.uptime.Reset()
+	for _, row := range rows {
+		e.uptime.WithLabelValues(row.logURL, row.endpoint).Set(row.ratio)
+	}
+	return nil
+}
+
+func (e *exporter) run(csvURL string, interval, jitter time.Duration) {
+	do := func() {
+		e.fetchAt.SetToCurrentTime()
+		if err := e.fetch(csvURL); err != nil {
+			log.Printf("fetch error: %v", err)
+			e.fetchOk.Set(0)
+		} else {
+			log.Printf("fetch ok")
+			e.fetchOk.Set(1)
+		}
+	}
+
+	do()
+	for {
+		delta := time.Duration(rand.Int63n(int64(2*jitter))) - jitter
+		sleep := interval + delta
+		log.Printf("next fetch in %s", sleep.Round(time.Second))
+		time.Sleep(sleep)
+		do()
+	}
+}
+
+func main() {
+	addr     := flag.String("listen",   ":9781",                                                     "address to listen on")
+	csvURL   := flag.String("url",      "https://www.gstatic.com/ct/compliance/endpoint_uptime_24h.csv", "URL of the uptime CSV")
+	interval := flag.Duration("interval", 12*time.Hour,  "how often to fetch the CSV")
+	jitter   := flag.Duration("jitter",    5*time.Minute, "maximum ±jitter applied to the fetch interval")
+	flag.Parse()
+
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}))
+	reg.MustRegister(prometheus.NewGoCollector())
+
+	exp := newExporter(reg)
+	go exp.run(*csvURL, *interval, *jitter)
+
+	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, `<html><body><a href="/metrics">metrics</a></body></html>`)
+	})
+
+	log.Printf("listening on %s", *addr)
+	log.Fatal(http.ListenAndServe(*addr, nil))
+}