What causes "podPort cannot be empty" in slimtoolkit/slim?

Pass a non-empty podPort (e.g. "8080") to PortForward

podPort cannot be empty

Error message

podPort cannot be empty

What it means

PortForward wraps `kubectl port-forward` and validates its inputs before exec'ing. A pod port is mandatory — without it kubectl has nothing to forward to — so an empty podPort is rejected immediately.

Source

Thrown at pkg/app/master/kubernetes/kubectl.go:140

		"exec", pod,
		"--kubeconfig", k.kubeconfig,
		"--namespace", namespace,
		"--container", container,
		"--", cmd,
	}, args...)
	return exec.Command(args[0], args[1:]...).CombinedOutput()
}

func (k *kubectl) PortForward(
	ctx context.Context,
	namespace string,
	pod string,
	address string,
	hostPort string,
	podPort string,
) (*exec.Cmd, string, error) {
	if podPort == "" {
		return nil, "", errors.New("podPort cannot be empty")
	}

	mapping := ":" + podPort
	if hostPort != "" {
		mapping = hostPort + mapping
	}

	cmd := exec.CommandContext(
		ctx,
		"kubectl",
		"--kubeconfig", k.kubeconfig,
		"--namespace", namespace,
		"--address", address,
		"port-forward", "pod/"+pod, mapping,
	)

	out, err := cmd.StdoutPipe()
	if err != nil {

View on GitHub (pinned to 81940d17fa)

Solutions

Pass a non-empty podPort (e.g. "8080") to PortForward
Validate the port value at config load time before invoking PortForward
Log/inspect where the port is derived from and fix the empty source

Example fix

// before
k.PortForward(ctx, pod, addr, hostPort, port) // port == ""
// after
if port == "" { port = "8080" }
k.PortForward(ctx, pod, addr, hostPort, port)

Defensive patterns

Strategy: validation

Validate before calling

if podPort == "" { return errors.New("podPort is required before calling PortForward") }
if _, err := strconv.Atoi(podPort); err != nil { return fmt.Errorf("podPort %q is not numeric", podPort) }

Try / catch

cmd, hp, err := k.PortForward(ctx, pod, addr, hostPort, podPort)
if err != nil && strings.Contains(err.Error(), "podPort cannot be empty") {
  return fmt.Errorf("config error: target port missing for pod %s", pod)
}

Prevention

Validate port fields at config-load time
Never pass raw env vars without empty checks
Fail fast with clear messages when parsing ports

When it happens

Trigger: Calling PortForward (public) with podPort set to "" — e.g. an unset/empty config field or an unparsed port variable passed through.

Common situations: Config file missing the target port; environment variable not set; parsing failure upstream silently yielding an empty string.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of slimtoolkit/slim@81940d17fa (2026-08-31). Data as JSON: /api/errors/6486db2aad1974f1. Report an issue: GitHub.