kovidgoyal/kitty · error

Failed to format the response as JSON: %w

Error message

Failed to format the response as JSON: %w

What it means

After successfully reading portal settings with --json, show_settings marshals the unwrapped map with json.MarshalIndent. Failure means the settings map contains a value Go's encoding/json cannot serialize (e.g. NaN, a channel, or an unsupported Variant payload type).

Source

Thrown at kittens/desktop_ui/portal.go:293

	conn, err := dbus.SessionBus()
	if err != nil {
		return fmt.Errorf("failed to connect to system bus with error: %w", err)
	}
	defer conn.Close()
	var response ReadAllType
	response, err = fetch_settings(conn, opts.InNamespace...)
	if opts.AsJson {
		unwrapped := make(map[string]map[string]any, len(response))
		for ns, m := range response {
			w := make(map[string]any, len(m))
			for k, a := range m {
				w[k] = a.Value()
			}
			unwrapped[ns] = w
		}
		j, err := json.MarshalIndent(unwrapped, "", "  ")
		if err != nil {
			return fmt.Errorf("Failed to format the response as JSON: %w", err)
		}
		fmt.Println(string(j))
	} else {
		for ns, m := range response {
			fmt.Println(ns + ":")
			for key, v := range m {
				fmt.Printf("\t%s: %s\n", key, v)
			}
		}
	}
	if !opts.AllowOtherBackends {
		is_running_self := false
		if m, found := response[SETTINGS_CANARY_NAMESPACE]; found {
			_, is_running_self = m[SETTINGS_CANARY_KEY]
		}
		if !is_running_self {
			err = fmt.Errorf("the settings did not come from the desktop-ui kitten. Some other portal backend is providing the service.")
		}

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Run without --json to print raw values and identify the offending key
2. Restrict output to specific namespaces to isolate the failing entry
3. Report/fix the backend that exposes the non-serializable value

Example fix

# before
kitten desktop-ui show-settings --json
# after
kitten desktop-ui show-settings --namespace=org.freedesktop.appearance --json

if err := showSettingsJSON(resp); err != nil {
    // fall back to plain-text printing
    printPlain(resp)
}

When it happens

Trigger: A portal namespace/key whose dbus.Variant stores a type that converts to an unmarshalable Go value (unsupported concrete types, cyclic structures).

Common situations: Non-standard portal backends exposing exotic variant types; extremely unusual settings values.

Related errors

• Could not encode message to kitty with error: %w
• failed to decode cached image metadata: %w
• must specify the new contrast value
• %s is not a valid contrast value
• must specify the key

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/aa0678b30405394f. Report an issue: GitHub.