moonD4rk/HackBrowserData · error

format %s: %w

Error message

format %s: %w

What it means

Writer.writeFile first formats all rows into a buffer so no file is created when a formatter emits nothing (e.g. cookie-editor skipping non-cookie data). This error wraps a failure inside formatter.format for a given category, meaning the category's rows could not be serialized (encoding error inside the CSV/JSON/cookie-editor writer).

Source

Thrown at output/output.go:139

	var s []categoryRows
	for _, cat := range categories {
		var rows []row
		for _, r := range o.results {
			rows = append(rows, cat.extract(r)...)
		}
		if len(rows) > 0 {
			s = append(s, categoryRows{cat.name, rows})
		}
	}
	return s
}

func (o *Writer) writeFile(category string, rows []row) (err error) {
	// Format to buffer first — if formatter produces no output (e.g.
	// cookie-editor skipping non-cookie data), don't create the file.
	var buf bytes.Buffer
	if err := o.formatter.format(&buf, rows); err != nil {
		return fmt.Errorf("format %s: %w", category, err)
	}
	if buf.Len() == 0 {
		return nil
	}

	filename := fmt.Sprintf("%s.%s", category, o.formatter.ext())
	path := filepath.Join(o.dir, filename)

	f, err := os.OpenFile(filepath.Clean(path), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
	if err != nil {
		return fmt.Errorf("create %s: %w", filename, err)
	}
	defer func() {
		if cerr := f.Close(); cerr != nil && err == nil {
			err = fmt.Errorf("close %s: %w", filename, cerr)
		}
	}()

View on GitHub (pinned to 0503d04d7a)

Solutions

1. Inspect the wrapped %w cause to identify which formatter and which row failed.
2. Sanitize row values before extraction (valid UTF-8, no NUL bytes) so the CSV/JSON encoders succeed.
3. Update to the latest version in case a formatter encoding bug is fixed upstream.
4. If using a custom formatter implementation, test format() against your actual row data.

Example fix

// before: raw bytes may not be valid UTF-8
rows[i].value = string(rawBytes)
// after
rows[i].value = strings.ToValidUTF8(string(rawBytes), "\uFFFD")

for _, r := range rows {
	for _, v := range r.values {
		if !utf8.ValidString(v) { return fmt.Errorf("row %q has invalid UTF-8", r.name) }
	}
}

if err := w.Write(); err != nil {
	if strings.Contains(err.Error(), "format ") {
		// wrapped formatter failure: inspect %w cause, sanitize rows, retry
	}
}

When it happens

Trigger: o.formatter.format(&buf, rows) returned an error while writing rows for the named category — e.g. a csv.Writer.Flush error from unencodable data or an internal JSON encode failure.

Common situations: Row values containing characters the CSV writer rejects or that trigger encoding errors; a custom/injected formatter with a bug; extremely large row sets hitting memory limits; formatter state corrupted by a prior call.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• write BOM: %w
• abe: base64 decode: %w
• encode dump: %w
• decode dump: %w
• unsupported dump version %q (this build expects %q)

AI-assisted analysis of moonD4rk/HackBrowserData@0503d04d7a (2026-09-06). Data as JSON: /api/errors/a26ff23e0e60e060. Report an issue: GitHub.