fix(cli): top, dashboard and cluster watch refuse an --interval under one second

cli/cmd/cluster_watch.go

@@ -41,6 +41,9 @@ var clusterWatchCmd = &cobra.Command{
 	Use:   "watch",
 	Short: "Live-watch Kafka cluster health (refreshing dashboard)",
 	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := checkInterval(clusterWatchInterval); err != nil {
+			return err
+		}
 		tick := 0
 		hist := &healthHistory{}
 

cli/cmd/dashboard.go

@@ -18,6 +18,9 @@ var dashboardCmd = &cobra.Command{
 	Aliases: []string{"dash"},
 	Short:   "Full-screen monitoring dashboard with live metrics",
 	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := checkInterval(dashInterval); err != nil {
+			return err
+		}
 		tick := 0
 		throughputHistory := make([]float64, 0, 30)
 		latencyHistory := make([]float64, 0, 30)

cli/cmd/interval_test.go

@@ -0,0 +1,49 @@
+package cmd
+
+import (
+	"errors"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/bmscomp/kates/cli/client"
+	"github.com/spf13/cobra"
+)
+
+// At --interval 0 the refresh loops never slept: top sent 20,347 requests in
+// 3 s to a stub API.
+func TestRefreshCommandsRefuseIntervalUnderOneSecond(t *testing.T) {
+	origClient, origTop, origDash, origWatch := apiClient, topInterval, dashInterval, clusterWatchInterval
+	t.Cleanup(func() {
+		apiClient, topInterval, dashInterval, clusterWatchInterval = origClient, origTop, origDash, origWatch
+	})
+	apiClient = client.Failing(errors.New("no API in this test"))
+
+	for _, tc := range []struct {
+		name     string
+		cmd      *cobra.Command
+		interval *int
+	}{
+		{"top", topCmd, &topInterval},
+		{"dashboard", dashboardCmd, &dashInterval},
+		{"cluster watch", clusterWatchCmd, &clusterWatchInterval},
+	} {
+		for _, seconds := range []int{0, -1} {
+			*tc.interval = seconds
+			done := make(chan error, 1)
+			go func() { done <- tc.cmd.RunE(tc.cmd, nil) }()
+			select {
+			case err := <-done:
+				if err == nil || !strings.Contains(err.Error(), "--interval must be at least 1 second") {
+					t.Errorf("%s --interval %d: err = %v, want the interval refused", tc.name, seconds, err)
+				}
+			case <-time.After(5 * time.Second):
+				t.Fatalf("%s --interval %d is still refreshing instead of refusing", tc.name, seconds)
+			}
+		}
+	}
+
+	if err := checkInterval(1); err != nil {
+		t.Errorf("checkInterval(1) = %v, want nil", err)
+	}
+}

cli/cmd/top.go

@@ -16,6 +16,9 @@ var topCmd = &cobra.Command{
 	Use:   "top",
 	Short: "Live view of running tests (like kubectl top)",
 	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := checkInterval(topInterval); err != nil {
+			return err
+		}
 		tick := 0
 
 		for {
@@ -120,3 +123,12 @@ func init() {
 	topCmd.Flags().IntVar(&topInterval, "interval", 2, "Refresh interval in seconds")
 	rootCmd.AddCommand(topCmd)
 }
+
+// checkInterval refuses a refresh interval under a second: at 0 or below the
+// refresh loops never slept, and sent thousands of requests a second.
+func checkInterval(seconds int) error {
+	if seconds < 1 {
+		return fmt.Errorf("--interval must be at least 1 second, got %d", seconds)
+	}
+	return nil
+}