gofiber/fiber · error

failed to lock: %w

Error message

failed to lock: %w

What it means

Returned by the middleware (idempotency.go:125-126) when cfg.Lock.Lock(key) fails. The default Locker is an in-process MemoryLock which only fails on context cancellation; a custom distributed Locker (Redis, etcd) can fail on connection loss or lock-acquisition timeout.

Source

Thrown at middleware/idempotency/idempotency.go:126

		if c.Get(cfg.KeyHeader) == "" {
			return c.Next()
		}

		// Validate key
		key := utils.CopyString(c.Get(cfg.KeyHeader))
		if err := cfg.KeyHeaderValidate(key); err != nil {
			return err
		}

		// First-pass: if the idempotency key is in the storage, get and return the response
		if ok, err := maybeWriteCachedResponse(c, key); err != nil {
			return fmt.Errorf("failed to write cached response at fastpath: %w", err)
		} else if ok {
			return nil
		}

		if err := cfg.Lock.Lock(key); err != nil {
			return fmt.Errorf("failed to lock: %w", err)
		}
		defer func() {
			if err := cfg.Lock.Unlock(key); err != nil {
				log.Errorf("[IDEMPOTENCY] failed to unlock key %q: %v", maskKey(key), err)
			}
		}()

		// Lock acquired. If the idempotency key now is in the storage, get and return the response
		if ok, err := maybeWriteCachedResponse(c, key); err != nil {
			return fmt.Errorf("failed to write cached response while locked: %w", err)
		} else if ok {
			return nil
		}

		// Execute the request handler
		if err := c.Next(); err != nil {
			// If the request handler returned an error, return it and skip idempotency
			return err

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Verify the Locker backend is reachable and healthy.
2. Make sure the Locker's per-key acquisition timeout exceeds your worst-case handler latency.
3. Cancel-protected clients: have upstream retries re-send the same idempotency key after a context-cancellation.
4. Consider whether a failure to lock should fall through (skip idempotency) rather than 500.

Example fix

// before
Lock: myRedisLock, // fails loudly on Redis blip

// after — Lock that returns nil on transient outage so the request proceeds
Lock: &tolerantLock{inner: myRedisLock}

// confirm distributed lock backend is up before wiring middleware
lock := redis.New(...)
if err := lock.Ping(); err != nil {
    log.Fatalf("lock backend down: %v", err)
}

// tolerate transient lock failures by proceeding without locking
// (idempotency may double-execute on retry, but the request succeeds)

When it happens

Trigger: Using a distributed Locker whose Lock(ctx, key) returns an error — Redis down, lock acquisition deadline exceeded, locker client misconfigured. The default in-memory locker only fails if the request context is already cancelled.

Common situations: Multi-instance deployment with a Redis-backed lock; client disconnected (context cancelled) while waiting behind another request with the same idempotency key; lock TTL shorter than the handler runtime causing acquisition thrash.

Related errors

• failed to read response: %w
• failed to write cached response while locked: %w
• failed to save response: %w
• invalid idempotency key
• cache: failed to reload key %q after eviction failure: %w

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/b5993b2a7bc3fd56.json. Report an issue: GitHub.