slackhq/nebula · error

error rx.Open(): %w

Error message

error rx.Open(): %w

What it means

This error wraps the failure of the receive (rx) ring buffer's Open() during RIO (Registered I/O) UDP listener setup on Windows. The rx side allocates the completion queue and receive buffers used by winrio; if that kernel resource setup fails, bind() aborts with the underlying OS error attached via %w. It is thrown by RIOConn.bind, invoked from NewRIOListener.

Source

Thrown at udp/udp_rio_windows.go:122

		// This is a best-effort to prevent errors from being returned by the udp recv operation.
		// Quietly log a failure and continue.
		l.Debug("failed to set UDP_CONNRESET ioctl", "error", err)
	}

	ret = 0
	flag = 0
	size = uint32(unsafe.Sizeof(flag))
	SIO_UDP_NETRESET := uint32(syscall.IOC_IN | syscall.IOC_VENDOR | 15)
	err = syscall.WSAIoctl(syscall.Handle(u.sock), SIO_UDP_NETRESET, (*byte)(unsafe.Pointer(&flag)), size, nil, 0, &ret, nil, 0)
	if err != nil {
		// This is a best-effort to prevent errors from being returned by the udp recv operation.
		// Quietly log a failure and continue.
		l.Debug("failed to set UDP_NETRESET ioctl", "error", err)
	}

	err = u.rx.Open()
	if err != nil {
		return fmt.Errorf("error rx.Open(): %w", err)
	}

	err = u.tx.Open()
	if err != nil {
		return fmt.Errorf("error tx.Open(): %w", err)
	}

	u.rq, err = winrio.CreateRequestQueue(u.sock, packetsPerRing, 1, packetsPerRing, 1, u.rx.cq, u.tx.cq, 0)
	if err != nil {
		return fmt.Errorf("error CreateRequestQueue: %w", err)
	}

	err = windows.Bind(u.sock, sa)
	if err != nil {
		return fmt.Errorf("error windows.Bind(): %w", err)
	}

	return nil

View on GitHub (pinned to dd8f660c0a)

Solutions

1. Read the wrapped %w OS error to identify the exact winrio failure (e.g. WSAEINVAL, WSAENOBUFS).
2. Reduce the packetsPerRing ring size so fewer registered buffers/non-paged pool is needed.
3. Ensure the process runs on a supported Windows version (Windows 8/Server 2012+) where RIO is fully available.
4. Retry after freeing memory / closing other RIO sockets if the cause is resource exhaustion.

Example fix

// before
err = u.rx.Open()
if err != nil {
	return fmt.Errorf("error rx.Open(): %w", err)
}
// after
err = u.rx.Open()
if err != nil {
	return fmt.Errorf("error rx.Open(): %w", err) // surface as ContextualError with fields {addr, port, side:"rx"} for diagnosability
}

if runtime.GOOS != "windows" { return errors.New("RIO listener only exists on windows") }
// verify the listen address is a valid local IP before NewListener
if net.ParseIP(addr) == nil { return fmt.Errorf("invalid listen addr %q", addr) }

func isRIOOpenErr(err error) bool { return err != nil && strings.Contains(err.Error(), "rx.Open()") }

conn, err := udp.NewListener(logger, settings)
if err != nil {
	var ctxErr *util.ContextualError
	if errors.As(err, &ctxErr) {
		logger.Error("udp rx ring open failed", "fields", ctxErr.Fields, "cause", ctxErr.Unwrap())
	}
	return fmt.Errorf("listener setup failed: %w", err)
}

When it happens

Trigger: Calling NewRIOListener (via udp.NewListener) on Windows when u.rx.Open() fails - typically winrio.CreateCompletionQueue or buffer registration returning an OS error (e.g. out of non-paged pool, insufficient privileges, or winsock RIO not initialized for the process).

Common situations: Windows hosts with resource exhaustion (non-paged pool depleted by many RIO sockets), running on Windows versions with incomplete RIO support, firewall/AV software interfering with raw socket setup, or extremely large packetsPerRing settings requiring huge registered buffer allocations.

Related errors

• error tx.Open(): %w
• error CreateRequestQueue: %w
• bind: %w
• init rx ring: %w
• winrio.Socket error: %w

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/32e201440cddc5a1. Report an issue: GitHub.