slimtoolkit/slim · error

error waiting for sensor event

Error message

error waiting for sensor event: %w

What it means

In runControlCommand, the 'wait-for-event' control command calls control.ExecuteWaitEvenCommand to block until the named event is received through the events file. If that wait fails (file I/O error, timeout, malformed event stream), the error is wrapped as 'error waiting for sensor event' and returned from Run.

Solutions

1. Check the wrapped inner error to distinguish file errors from timeouts.
2. Confirm the events file path (eventsFilePath()) points to a writable, existing directory.
3. Verify the event name (os.Args[3]) exactly matches an event the target app emits.
4. Increase the context timeout if the event legitimately takes long to fire.

if len(os.Args) < 4 {
    return errors.New("missing event name")
}
if _, err := os.Stat(filepath.Dir(eventsFilePath())); err != nil {
    return fmt.Errorf("events dir missing: %w", err)
}

func isValidEventType(name string) bool {
    _, ok := event.TypeFromString(name) // or membership check in known events
    return ok
}

err := app.Run(ctx)
if err != nil {
    if errors.Is(err, context.DeadlineExceeded) && strings.Contains(err.Error(), "waiting for sensor event") {
        return fmt.Errorf("event %q never arrived within deadline; check event name and emitter", os.Args[3])
    }
    return err
}

When it happens

Trigger: Running the sensor with the WaitForEventCommand and an event name from os.Args[3] while ExecuteWaitEvenCommand fails — events file cannot be created/read, the expected event never arrives before the context is cancelled, or the event type is invalid.

Common situations: Context deadline exceeded because the target app never emitted the event; events file directory deleted or read-only; typo in the event name so the sensor waits forever then times out.

Related errors

• error stopping target app
• missing command
• missing event name
• start monitor timeout
• start monitor timeout

AI-assisted analysis of slimtoolkit/slim@81940d17fa (2026-08-31). Data as JSON: /api/errors/169b18f8661245a1. Report an issue: GitHub.

Appendix: source

Thrown at pkg/app/sensor/app.go:321

func runControlCommand(ctx context.Context) error {
	if len(os.Args) < 3 {
		return errors.New("missing command")
	}

	cmd := control.Command(os.Args[2])

	switch cmd {
	case control.StopTargetAppCommand:
		if err := control.ExecuteStopTargetAppCommand(ctx, *commandsFile); err != nil {
			return fmt.Errorf("error stopping target app: %w", err)
		}

	case control.WaitForEventCommand:
		if len(os.Args) < 4 {
			return errors.New("missing event name")
		}
		if err := control.ExecuteWaitEvenCommand(ctx, eventsFilePath(), event.Type(os.Args[3])); err != nil {
			return fmt.Errorf("error waiting for sensor event: %w", err)
		}

	default:
		return fmt.Errorf("unknown command: %s", cmd)
	}

	return nil
}

View on GitHub (pinned to 81940d17fa)