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cmd/ffd-metrics/main.go

@@ -0,0 +1,93 @@
+// Command ffd-metrics is the long-running metrics daemon for the federated
+// forge indexer.
+//
+// It reads the same SQLite store the indexer writes to and exposes the state
+// of the index to Prometheus at /metrics. It is intended to be run as a
+// separate systemd service; it performs no scraping of its own.
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.yaml.in/yaml/v4"
+
+	"git.xengi.de/ffd/indexer/config"
+	"git.xengi.de/ffd/indexer/internal/version"
+	"git.xengi.de/ffd/indexer/metrics"
+	"git.xengi.de/ffd/indexer/store"
+)
+
+func main() {
+	configPath := flag.String("config", "config.yaml", "path to the configuration file")
+	showVersion := flag.Bool("version", false, "print version and commit, then exit")
+	flag.Parse()
+
+	if *showVersion {
+		version.PrintFull()
+		return
+	}
+
+	data, err := os.ReadFile(*configPath)
+	if err != nil {
+		panic(err)
+	}
+	var cfg config.Config
+	if err := yaml.Unmarshal(data, &cfg); err != nil {
+		panic(err)
+	}
+
+	// The daemon shares the indexer's database; both processes may be open on
+	// it at once (the SQLite driver handles that with WAL-safe read queries).
+	db, err := store.Open(cfg.DbPath)
+	if err != nil {
+		panic(err)
+	}
+	defer func() { _ = db.Close() }()
+
+	registry := prometheus.NewRegistry()
+	registry.MustRegister(metrics.NewCollector(db))
+
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", promhttp.HandlerFor(registry, promhttp.HandlerOpts{}))
+
+	srv := &http.Server{
+		Addr:              cfg.Metrics.Listen,
+		Handler:           mux,
+		ReadHeaderTimeout: 5 * time.Second,
+	}
+
+	// Shut down cleanly on SIGTERM/SIGINT.
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM, os.Interrupt)
+	defer stop()
+
+	errCh := make(chan error, 1)
+	go func() {
+		fmt.Printf("ffd-metrics listening on %s\n", srv.Addr)
+		errCh <- srv.ListenAndServe()
+	}()
+
+	select {
+	case err := <-errCh:
+		if err != nil && !errors.Is(err, http.ErrServerClosed) {
+			fmt.Fprintf(os.Stderr, "metrics server: %v\n", err)
+			os.Exit(1)
+		}
+	case <-ctx.Done():
+		fmt.Println("shutting down")
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if err := srv.Shutdown(shutdownCtx); err != nil {
+			fmt.Fprintf(os.Stderr, "shutdown: %v\n", err)
+		}
+	}
+}