gofiber/fiber · error

limiter: failed to marshal key

Error message

limiter: failed to marshal key %q: %w

What it means

Before writing an item to external storage, the manager calls it.MarshalMsg(nil) (msgp-generated). For this simple struct (three numeric fields), MarshalMsg is essentially incapable of failing under normal conditions; an error indicates a corrupted generated code path, nil receiver, or an internal msgp invariant violation.

Solutions

1. Regenerate the msgp code: go run github.com/tinylib/msgp -o=manager_msgp.go -tests=false -unexported in middleware/limiter.
2. Run go mod tidy to align the msgp runtime library version with the generator version.
3. Clear the Go build cache: go clean -cache and rebuild.
4. Confirm the item struct in manager.go matches the msgp tag expectations (no missing/renamed fields).

Example fix

// before: stale generated code
// manager_msgp.go out of sync with item struct

// after: regenerate
// run: go generate ./middleware/limiter/...

// CI step: regenerate and diff msgp output to catch drift.
// go generate ./middleware/limiter/... && git diff --exit-code manager_msgp.go

When it happens

Trigger: Effectively unreachable in production. Theoretical triggers: msgp-generated code out of sync with the struct (go generate not re-run after a field change), memory pressure causing an allocation failure inside the encoder, or a manually edited manager_msgp.go.

Common situations: Developer hand-edited manager_msgp.go; msgp version skew between the version that generated the file and the version imported at build time; corrupt build cache.

Related errors

• failed to marshal response
• limiter: failed to unmarshal key
• limiter: unexpected entry type %T for key
• binder: msgpack is not configured, please check docs…
• failed to unmarshal response

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/e3f0f0b14ce5811b. Report an issue: GitHub.

Appendix: 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 a105acad6c)