Method Open

platform/windows/backend.go:57–98

Open installs a WinDivert filter matching scope and starts the recv loop. Requires Administrator and the WinDivert driver installed.

(ctx context.Context, scope snixplatform.Scope)

// Open installs a WinDivert filter matching scope and starts the recv loop.
// Requires Administrator and the WinDivert driver installed.
func (b *Backend) Open(ctx context.Context, scope snixplatform.Scope) error {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.opened {
		return errors.New("snix/windows: backend already open")
	}
	if !scope.RemoteIP.Is4() {
		return fmt.Errorf("snix/windows: IPv6 scope not yet supported (%s)", scope.RemoteIP)
	}

	// Fail fast with a clear message when not elevated. WinDivertOpen will
	// also reject us, but this check runs before we even touch the DLL so
	// diagnostics are crisp (no "WinDivertOpen: ERROR_ACCESS_DENIED" noise).
	if elevated, err := IsElevated(); err != nil {
		return fmt.Errorf("snix/windows: privilege check failed: %w", err)
	} else if !elevated {
		return fmt.Errorf("%w; relaunch from an elevated shell (Run as Administrator)", ErrNotElevated)
	}

	filter := fmt.Sprintf(
		"tcp and ip and ((ip.DstAddr == %s and tcp.DstPort == %d) or (ip.SrcAddr == %s and tcp.SrcPort == %d))",
		scope.RemoteIP, scope.RemotePort, scope.RemoteIP, scope.RemotePort)

	h, err := Open(filter, LayerNetwork, b.cfg.Priority, FlagDefault)
	if err != nil {
		return err
	}
	if b.cfg.QueueLength > 0 {
		if e := SetParam(h, ParamQueueLength, b.cfg.QueueLength); e != nil {
			_ = Close(h)
			return fmt.Errorf("SetParam QueueLength: %w", e)
		}
	}

	b.handle = h
	b.scope = scope
	b.opened = true

	b.reader.Add(1)
	go b.recvLoop(ctx)
	return nil
}

// recvLoop reads WinDivert packets and forwards them on b.packets.
// The caller's Verdict decides whether the packet is reinjected (Accept),