Invalid base64 encoded data from terminal with error: %w

Error message

Invalid base64 encoded data from terminal with error: %w

What it means

When reading the clipboard from the terminal, the kitten sends an OSC 52-style query and expects the reply base64-encoded. If the returned data cannot be base64-decoded, this error is raised. The terminal sent garbage instead of valid base64.

Source

Thrown at kittens/clipboard/legacy.go:198

	var clipboard_contents []byte

	lp.OnEscapeCode = func(etype loop.EscapeCodeType, data []byte) (err error) {
		switch etype {
		case loop.DCS:
			if strings.HasPrefix(utils.UnsafeBytesToString(data), "1+r") {
				lp.Quit(0)
			}
		case loop.OSC:
			q := utils.UnsafeBytesToString(data)
			if strings.HasPrefix(q, "52;") {
				parts := strings.SplitN(q, ";", 3)
				if len(parts) < 3 {
					lp.Quit(0)
					return
				}
				data, err := base64.StdEncoding.DecodeString(parts[2])
				if err != nil {
					return fmt.Errorf("Invalid base64 encoded data from terminal with error: %w", err)
				}
				clipboard_contents = data
				lp.Quit(0)
			}
		}
		return
	}

	esc_count := 0
	lp.OnKeyEvent = func(event *loop.KeyEvent) error {
		if event.MatchesPressOrRepeat("ctrl+c") || event.MatchesPressOrRepeat("esc") {
			if transmitting {
				return nil
			}
			event.Handled = true
			esc_count++
			if esc_count < 2 {
				key := "Esc"

View on GitHub (pinned to 6d5d0c4406)

Solutions

Run outside tmux/screen or enable proper escape-sequence passthrough
Update kitty and the terminal emulator
Check that shell integration/prompt isn't injecting escape codes that answer queries

Defensive patterns

Strategy: validation

Validate before calling

if _, err := base64.StdEncoding.DecodeString(parts[2]); err != nil {
	return errors.New("terminal clipboard reply not base64; run inside kitty without multiplexer mangling")
}

Try / catch

data, err := base64.StdEncoding.DecodeString(s)
if err != nil { return nil, fmt.Errorf("bad clipboard payload: %w", err) }

Prevention

Run clipboard get directly in kitty, not through tmux/screen
Keep shell prompt escape codes from answering terminal queries

When it happens

Trigger: Asking the terminal for clipboard contents (get mode) where the reply's third part fails base64.StdEncoding.DecodeString — e.g. corrupted or empty payload, or another program answered the query.

Common situations: Running inside tmux/screen that mangles DCS/OSC replies, shell prompt escape sequences interfering with terminal queries, non-kitty terminals with partial OSC 52 support.

Related errors

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/a6d0547d97cd178e. Report an issue: GitHub.