moonD4rk/HackBrowserData · error

write BOM: %w

Error message

write BOM: %w

What it means

For CSV output, writeFile writes a 3-byte UTF-8 BOM before the formatted content so Excel detects UTF-8. This error wraps a failed f.Write of that BOM, meaning even the first bytes of the file could not be written — the output file will be missing or invalid.

Source

Thrown at output/output.go:160

		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)
		}
	}()

	if strings.HasSuffix(path, ".csv") {
		if _, err := f.Write(utf8BOM); err != nil {
			return fmt.Errorf("write BOM: %w", err)
		}
	}

	if _, err := f.Write(buf.Bytes()); err != nil {
		return fmt.Errorf("write %s: %w", filename, err)
	}
	return nil
}

View on GitHub (pinned to 0503d04d7a)

Solutions

1. Free disk space on the output volume and retry.
2. Write output to a reliable local filesystem rather than network/removable mounts.
3. Verify the file handle is valid (no early Close) and re-run the extraction.
4. Check container/volume size limits if writing into tmpfs or small volumes.

Example fix

// before
if _, err := f.Write(utf8BOM); err != nil {
	return fmt.Errorf("write BOM: %w", err)
}
// after: check the short-write case explicitly
if n, err := f.Write(utf8BOM); err != nil || n != len(utf8BOM) {
	return fmt.Errorf("write BOM: wrote %d bytes: %w", n, err)
}

if st, err := os.Stat(outputDir); err == nil {
	_ = st // also verify volume free space > expected output size before writing
}

if err := w.Write(); err != nil {
	if strings.Contains(err.Error(), "write BOM") {
		// handle write failed immediately after open: check disk/handle, retry
	}
}

When it happens

Trigger: f.Write(utf8BOM) returned a short write or error right after a successful OpenFile: disk full, handle closed/invalid, or the file descriptor became unwritable between open and write.

Common situations: Disk filled between file creation and write; file opened on a flaky network/USB volume; extremely constrained environments (containers with tiny tmpfs output dirs).

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

• create output dir: %w
• format %s: %w
• create %s: %w
• close %s: %w
• create temp dir: %w

AI-assisted analysis of moonD4rk/HackBrowserData@0503d04d7a (2026-09-06). Data as JSON: /api/errors/22ade0da87f65fa5. Report an issue: GitHub.