moonD4rk/HackBrowserData · error

unsupported format: %s

Error message

unsupported format: %s

What it means

newFormatter maps a user-supplied output format name to a formatter implementation (csv, json, cookie-editor). Any other name is rejected at writer construction time, before any data is extracted or written. This is a fail-fast validation of the --format CLI/config value.

Source

Thrown at output/formatter.go:23

	"io"
)

// formatter serializes rows to a writer. Unexported — only used by Writer.
type formatter interface {
	format(w io.Writer, rows []row) error
	ext() string
}

func newFormatter(name string) (formatter, error) {
	switch name {
	case "csv":
		return &csvFormatter{}, nil
	case "json":
		return &jsonFormatter{}, nil
	case "cookie-editor":
		return &cookieEditorFormatter{fallback: &jsonFormatter{}}, nil
	default:
		return nil, fmt.Errorf("unsupported format: %s", name)
	}
}

View on GitHub (pinned to 0503d04d7a)

Solutions

1. Pass one of the exact supported names: csv, json, or cookie-editor (case-sensitive).
2. Normalize the input to lowercase before calling NewWriter: strings.ToLower(format).
3. Check the CLI help / NewWriter docs for the current supported format list.
4. If another format is genuinely needed, add a formatter case in output/formatter.go implementing the formatter interface.

Example fix

// before
w, err := output.NewWriter(dir, "JSON", nil) // unsupported
// after
w, err := output.NewWriter(dir, strings.ToLower("JSON"), nil) // "json"

var supported = map[string]bool{"csv": true, "json": true, "cookie-editor": true}
if !supported[format] {
	return fmt.Errorf("format %q not supported; use csv, json, or cookie-editor", format)
}

func isValidFormat(s string) bool {
	switch s { case "csv", "json", "cookie-editor": return true }
	return false
}

w, err := output.NewWriter(dir, format, nil)
if err != nil && strings.Contains(err.Error(), "unsupported format") {
	w, err = output.NewWriter(dir, "json", nil) // default fallback
}

When it happens

Trigger: NewWriter (via newFormatter) was called with a format name outside the supported set {csv, json, cookie-editor}, e.g. 'yaml', 'JSON' (case-sensitive), or an empty string.

Common situations: Typo in the CLI flag (--format jsn); wrong casing since the switch is case-sensitive; users assuming XML/YAML/HTML output exists; scripts passing a variable built from config that defaults to an unsupported value.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• yandex: encrypted intermediate key truncated
• abe: encrypted key too short: %d bytes
• abe: unexpected prefix: got %q, want %q
• encrypted_key too short: %d bytes
• encrypted_key unexpected prefix: got %q, want %q

AI-assisted analysis of moonD4rk/HackBrowserData@0503d04d7a (2026-09-06). Data as JSON: /api/errors/d232f5a4601693f8. Report an issue: GitHub.