Add prometheus exporter on :9100

cmd/collector/main.go

@@ -6,6 +6,7 @@ import (
 	"flag"
 	"log"
 	"net"
+	"net/http"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -19,6 +20,7 @@ import (
 
 func main() {
 	listen := flag.String("listen", ":9090", "gRPC listen address")
+	promListen := flag.String("prom-listen", ":9100", "Prometheus metrics listen address (empty to disable)")
 	logPaths := flag.String("logs", "", "comma-separated log file paths/globs to tail")
 	logsFile := flag.String("logs-file", "", "file containing one log path/glob per line")
 	source := flag.String("source", hostname(), "name for this collector (default: hostname)")
@@ -40,6 +42,18 @@ func main() {
 	ch := make(chan LogRecord, 200_000)
 
 	store := NewStore(*source)
+	if *promListen != "" {
+		ps := NewPromStore()
+		store.prom = ps
+		mux := http.NewServeMux()
+		mux.Handle("/metrics", ps)
+		go func() {
+			log.Printf("collector: Prometheus metrics on %s/metrics", *promListen)
+			if err := http.ListenAndServe(*promListen, mux); err != nil {
+				log.Fatalf("collector: Prometheus server: %v", err)
+			}
+		}()
+	}
 	go store.Run(ch)
 
 	tailer := NewMultiTailer(patterns, *scanInterval, *v4prefix, *v6prefix, ch)