FiloSottile/age · warning

failed to re-serialize header: %w

Error message

failed to re-serialize header: %w

What it means

After parsing, Inspect re-serializes the header with hdr.Marshal into a bytes.Buffer to measure its size. Writes to a bytes.Buffer only fail on OOM, so this is nearly impossible in practice; the wrap exists for completeness of the error path.

Source

Thrown at internal/inspect/inspect.go:57

	tr := &trackReader{r: r}
	br := bufio.NewReader(tr)
	const maxWhitespace = 1024
	start, _ := br.Peek(maxWhitespace + len(armor.Header))
	if strings.HasPrefix(string(bytes.TrimSpace(start)), armor.Header) {
		r = armor.NewReader(br)
		data.Armor = true
	} else {
		r = br
	}

	hdr, rest, err := format.Parse(r)
	if err != nil {
		return nil, fmt.Errorf("failed to read header: %w", err)
	}

	buf := &bytes.Buffer{}
	if err := hdr.Marshal(buf); err != nil {
		return nil, fmt.Errorf("failed to re-serialize header: %w", err)
	}
	data.Sizes.Header = int64(buf.Len())

	for _, s := range hdr.Recipients {
		data.StanzaTypes = append(data.StanzaTypes, s.Type)
		switch s.Type {
		case "X25519", "ssh-rsa", "ssh-ed25519", "p256tag", "piv-p256":
			data.Postquantum = "no"
		case "mlkem768x25519", "scrypt", "mlkem768p256tag":
			// Keep "yes".
		default:
			if data.Postquantum != "no" {
				data.Postquantum = "unknown"
			}
		}
	}

	// If fileSize is not provided, or if it's the size of the armored file

View on GitHub (pinned to b74dce4cdb)

Solutions

1. Check available memory if processing pathological inputs
2. Reduce the number of recipient stanzas when generating files
3. Report a bug if this reproduces with normal files — it indicates a Marshal implementation issue

// Marshal targets a bytes.Buffer; nothing useful can be validated beforehand.

if err != nil { /* treat as OOM/systemic; retry or abort */ }

var buf bytes.Buffer
if err := hdr.Marshal(&buf); err != nil {
    return nil, fmt.Errorf("header re-serialization failed (memory?): %w", err)
}

When it happens

Trigger: hdr.Marshal(buf) returns non-nil while Inspect measures data.Sizes.Header — effectively only under memory exhaustion or a custom Marshal failure.

Common situations: Extremely large headers with the maximum number of recipient stanzas on memory-constrained systems; essentially never in normal use.

Related errors

• invalid stanza type: %q
• invalid stanza argument: %q
• failed to read header: %w
• failed to read rest of file: %w
• failed to compute stream overhead: %w

AI-assisted analysis of FiloSottile/age@b74dce4cdb (2026-08-31). Data as JSON: /api/errors/0f1bc212b47af104. Report an issue: GitHub.