What causes "failed to scan kubectl event stream: %w" in lima-vm/lima?

Increase the scanner buffer: scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024) before the scan loop.

failed to scan kubectl event stream: %w

Error message

failed to scan kubectl event stream: %w

What it means

The bufio.Scanner used to read the kubectl JSON watch stream returned a non-EOF error, such as a line exceeding the scanner's token buffer size. The stream reader aborts and this error is propagated to startAndStreamKubectl.

Source

Thrown at pkg/guestagent/kubernetesservice/kubernetesservice.go:190

		if err := json.Unmarshal(ev.Object, &svc); err != nil {
			return fmt.Errorf("failed to unmarshal service object: %w (line=%#q)", err, line)
		}

		key := svc.Metadata.Namespace + "/" + svc.Metadata.Name
		s.rwMutex.Lock()
		switch ev.Type {
		case added, modified:
			s.serviceSpecs[key] = &svc.Spec
		case deleted:
			delete(s.serviceSpecs, key)
		default:
			// NOP
		}
		s.rwMutex.Unlock()
	}

	if err := scanner.Err(); err != nil {
		return fmt.Errorf("failed to scan kubectl event stream: %w", err)
	}
	return nil
}

func (s *ServiceWatcher) GetPorts() []Entry {
	s.rwMutex.RLock()
	defer s.rwMutex.RUnlock()

	var entries []Entry
	for key, spec := range s.serviceSpecs {
		if spec.Type != serviceTypeNodePort &&
			spec.Type != serviceTypeLoadBalancer {
			continue
		}

		for _, portEntry := range spec.Ports {
			switch portEntry.Protocol {
			case protocolTCP, protocolUDP:

View on GitHub (pinned to dd909d0973)

Solutions

Increase the scanner buffer: scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024) before the scan loop.
Reduce Service annotation/status size on the cluster if lines are genuinely huge.
Check for pipe/I/O errors underlying the scan failure and restart the kubectl watcher.

Example fix

// before
canner := bufio.NewScanner(stdout)
// after
scanner := bufio.NewScanner(stdout)
scanner.Buffer(make([]byte, 0, 64*1024), 4*1024*1024)

Defensive patterns

Strategy: fallback

Validate before calling

// ensure the scanner can handle large lines before scanning
scanner := bufio.NewScanner(stdout)
scanner.Buffer(make([]byte, 0, 64*1024), 4*1024*1024)

Try / catch

if err := readKubectlStream(stdout); err != nil {
	if errors.Is(err, bufio.ErrTooLong) || strings.Contains(err.Error(), "failed to scan kubectl event stream") {
		log.WithError(err).Warn("event stream scan failed; restarting watcher")
		go restartWatcher()
		return nil
	}
	return err
}

Prevention

Always raise the scanner buffer above the default 64KB for kubectl output.
Avoid giant Service annotations in the watched cluster.
Restart the watcher on scan errors instead of dying permanently.
Monitor for recurring scan failures indicating oversized objects.

When it happens

Trigger: readKubectlStream when scanner.Scan() sets scanner.Err(), most commonly bufio.ErrTooLong from a JSON line larger than the default 64KB scanner buffer (a Service with a very large spec/status, huge annotations).

Common situations: Services with massive annotation payloads (e.g. ELB status annotations) producing watch lines > 64KB; I/O error on the pipe to kubectl.

Related errors

AI-assisted analysis of lima-vm/lima@dd909d0973 (2026-09-01). Data as JSON: /api/errors/1fcf080e67b64d73. Report an issue: GitHub.