shadow1ng/fscan · error

result cannot be nil

Error message

result cannot be nil

What it means

Argument guard in Manager.SaveResult: the method was invoked with a nil *ScanResult, which cannot be serialized to any output writer. It is a programmer/API-contract error (caller passed nil), distinct from the 'output manager is closed' state check that precedes it.

Source

Thrown at common/output/manager.go:81

	if err != nil {
		return err
	}

	m.writer = writer
	return m.writer.WriteHeader()
}

// SaveResult 保存扫描结果
func (m *Manager) SaveResult(result *ScanResult) error {
	m.mu.RLock()
	defer m.mu.RUnlock()

	if m.closed {
		return fmt.Errorf("output manager is closed")
	}

	if result == nil {
		return fmt.Errorf("result cannot be nil")
	}

	return m.writer.Write(result)
}

// Flush 刷新输出
func (m *Manager) Flush() error {
	m.mu.RLock()
	defer m.mu.RUnlock()

	if m.closed {
		return fmt.Errorf("output manager is closed")
	}

	return m.writer.Flush()
}

// Close 关闭输出管理器

View on GitHub (pinned to 95cc12e753)

Solutions

1. Check results for nil before calling SaveResult
2. Ensure scan functions return an error alongside nil results so callers can skip
3. Filter nil entries out of result slices before persisting

Example fix

// before
mgr.SaveResult(res) // res may be nil
// after
if res != nil {
    mgr.SaveResult(res)
}

if res == nil {
    return errors.New("no scan result to save")
}
return mgr.SaveResult(res)

func hasResult(r *ScanResult) bool { return r != nil }

if err := mgr.SaveResult(res); err != nil {
    if strings.Contains(err.Error(), "result cannot be nil") {
        log.Debug("skipping nil result")
        return nil
    }
    return err
}

When it happens

Trigger: Passing nil to SaveResult, e.g. when a scan stage produced no result or an upstream function returned (nil, nil) and the caller forwards it unchecked.

Common situations: Pipeline code where a failed probe returns nil result without an error, appending nil in a results slice and flushing it, tests like TestManager_SaveNilResult.

Related errors

• result cannot be nil
• output config cannot be nil
• unsupported format: %s
• output manager is closed
• failed to create TXT file: %w

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/19fe1fc7f25f1c76. Report an issue: GitHub.