only run prometheus client if metric-addr present

main.go

@@ -205,7 +205,7 @@ var (
 	})
 )
 
-func init() {
+func registerMetrics() {
 	prometheus.MustRegister(promRequests)
 	prometheus.MustRegister(promSuccesses)
 	prometheus.MustRegister(promLatencyHistogram)
@@ -227,7 +227,7 @@ func main() {
 	headers := make(headerSet)
 	flag.Var(&headers, "header", "HTTP request header. (can be repeated.)")
 	data := flag.String("data", "", "HTTP request data")
-	addr := flag.String("addr", ":8505", "service port to run on")
+	metricAddr := flag.String("metric-addr", "", "port to serve metrics on")
 
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Usage: %s <url> [flags]\n", path.Base(os.Args[0]))
@@ -316,10 +316,13 @@ func main() {
 	interrupted := make(chan os.Signal, 2)
 	signal.Notify(interrupted, syscall.SIGINT)
 
-	go func() {
-		http.Handle("/metrics", promhttp.Handler())
-		http.ListenAndServe(*addr, nil)
-	}()
+	if *metricAddr != "" {
+		registerMetrics()
+		go func() {
+			http.Handle("/metrics", promhttp.Handler())
+			http.ListenAndServe(*metricAddr, nil)
+		}()
+	}
 
 	for {
 		select {