start http only after successful scrape

main.go

@@ -88,6 +88,16 @@ func readRegs(client modbus.Client, start, qty uint16) {
 	}
 }
 
+func scrape(client modbus.Client) {
+	start := time.Now()
+	scrapeStart.SetToCurrentTime()
+	readRegs(client, 5000, 50)
+	readRegs(client, 5100, 50)
+	scrapeEnd.SetToCurrentTime()
+	scrapeDuration.Set(time.Since(start).Seconds())
+	scrapeCounter.Inc()
+}
+
 func main() {
 	flag.Parse()
 	scrapeIntervalGauge.Set(float64(*scrapeInterval))
@@ -117,10 +127,9 @@ func main() {
 		io.Copy(conn, sgc)
 	}()
 
-	// HTTP stuff
+	// HTTP setup
 	http.Handle("/metrics", promhttp.Handler())
 	http.HandleFunc("/", statusHandler)
-	go http.ListenAndServe(*httpAddr, nil)
 
 	// Modbus scrape loop
 	handler := modbus.NewTCPClientHandler(ln.Addr().String())
@@ -128,17 +137,10 @@ func main() {
 	handler.Connect()
 	defer handler.Close()
 	client := modbus.NewClient(handler)
-
-	ticker := time.Tick(*scrapeInterval)
-	for {
-		start := time.Now()
-		scrapeStart.SetToCurrentTime()
-		readRegs(client, 5000, 50)
-		readRegs(client, 5100, 50)
-		scrapeEnd.SetToCurrentTime()
-		scrapeDuration.Set(time.Since(start).Seconds())
-		scrapeCounter.Inc()
-
-		<-ticker
+	scrape(client)
+	// Start http interface only after first successful scrape
+	go http.ListenAndServe(*httpAddr, nil)
+	for range time.Tick(*scrapeInterval) {
+		scrape(client)
 	}
 }