slimtoolkit/slim · error

error waiting for sensor event: %w

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.

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)

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

• start monitor timeout
• start monitor timeout
• unknown sensor mode
• missing command
• missing event name

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