gofiber/fiber · error

limiter: failed to marshal key %q: %w

Error message

limiter: failed to marshal key %q: %w

What it means

Returned by manager.set when the *item cannot be serialized via msgp (MarshalMsg) before writing to external storage. This is the encoding counterpart of the unmarshal error.

Source

Thrown at middleware/limiter/manager.go:102

	if value == nil {
		return m.acquire(), nil
	}

	it, ok := value.(*item)
	if !ok {
		return nil, fmt.Errorf("limiter: unexpected entry type %T for key %q", value, m.logKey(key))
	}

	return it, nil
}

// set data to storage or memory
func (m *manager) set(ctx context.Context, key string, it *item, exp time.Duration) error {
	if m.storage != nil {
		raw, err := it.MarshalMsg(nil)
		if err != nil {
			m.release(it)
			return fmt.Errorf("limiter: failed to marshal key %q: %w", m.logKey(key), err)
		}
		if err := m.storage.SetWithContext(ctx, key, raw, exp); err != nil {
			m.release(it)
			return fmt.Errorf("limiter: failed to store key %q: %w", m.logKey(key), err)
		}
		m.release(it)
		return nil
	}

	m.memory.Set(key, it, exp)
	return nil
}

func (m *manager) logKey(key string) string {
	if m.shouldRedactKeys {
		return redactedKey
	}
	return key

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Regenerate msgp code: run `make generate` (or `go generate ./middleware/limiter/...`).
2. Confirm the installed msgp version matches the one referenced in AGENTS.md/Makefile.
3. Rebuild the binary from a clean cache to rule out stale generated code.

// Guard codegen sync at build time: ensure generated msgp is current.
// In CI, run: go generate ./middleware/limiter/... && git diff --exit-code

// A marshal failure is effectively unrecoverable at runtime; log and
// return 500.
if strings.Contains(err.Error(), "failed to marshal key") {
    log.Error().Err(err).Msg("limiter msgp marshal failed")
    return c.Status(500).SendString("internal error")
}

When it happens

Trigger: it.MarshalMsg(nil) fails at manager.go:99. msgp marshaling of the simple item struct (three numeric fields) is essentially infallible in practice; hitting this indicates a broken/generated msgp implementation, memory corruption, or an extremely unusual runtime fault.

Common situations: Running generated manager_msgp.go that is out of sync with the item struct (forgot to run go generate); msgp codegen version mismatch; memory corruption.

Related errors

• limiter: failed to unmarshal key %q: %w
• failed to unmarshal response: %w
• limiter: failed to persist state: %w
• limiter: failed to persist state: %w
• limiter: failed to get key %q from storage: %w

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/e3f0f0b14ce5811b.json. Report an issue: GitHub.