metrics: allow server to return errors

metricsserver/metrics.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"golang.org/x/sync/errgroup"
 
 	"go.ntppool.org/common/logger"
 )
@@ -41,7 +42,10 @@ func (m *Metrics) Handler() http.Handler {
 	})
 }
 
-func (m *Metrics) ListenAndServe(ctx context.Context, port int) {
+// ListenAndServe starts a goroutine with a server running on
+// the specified port. The server will shutdown and return when
+// the provided context is done
+func (m *Metrics) ListenAndServe(ctx context.Context, port int) error {
 
 	log := logger.Setup()
 
@@ -53,16 +57,23 @@ func (m *Metrics) ListenAndServe(ctx context.Context, port int) {
 		Handler:      m.Handler(),
 	}
 
-	go func() {
+	g, ctx := errgroup.WithContext(ctx)
+
+	g.Go(func() error {
 		err := srv.ListenAndServe()
-		if err != http.ErrServerClosed {
+		if err != nil && err != http.ErrServerClosed {
 			log.Warn("metrics server done listening", "err", err)
+			return err
 		}
-	}()
+		return nil
+	})
 
 	<-ctx.Done()
 
 	if err := srv.Shutdown(ctx); err != nil {
 		log.Error("metrics server shutdown failed", "err", err)
+		return err
 	}
+
+	return g.Wait()
 }