[client] Add NAT-PMP/UPnP support (#5202)

client/internal/portforward/state.go

@@ -0,0 +1,50 @@
+//go:build !js
+
+package portforward
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/libp2p/go-nat"
+	log "github.com/sirupsen/logrus"
+)
+
+// discoverGateway is the function used for NAT gateway discovery.
+// It can be replaced in tests to avoid real network operations.
+var discoverGateway = nat.DiscoverGateway
+
+// State is persisted only for crash recovery cleanup
+type State struct {
+	InternalPort uint16 `json:"internal_port,omitempty"`
+	Protocol     string `json:"protocol,omitempty"`
+}
+
+func (s *State) Name() string {
+	return "port_forward_state"
+}
+
+// Cleanup implements statemanager.CleanableState for crash recovery
+func (s *State) Cleanup() error {
+	if s.InternalPort == 0 {
+		return nil
+	}
+
+	log.Infof("cleaning up stale port mapping for port %d", s.InternalPort)
+
+	ctx, cancel := context.WithTimeout(context.Background(), discoveryTimeout)
+	defer cancel()
+
+	gateway, err := discoverGateway(ctx)
+	if err != nil {
+		// Discovery failure is not an error - gateway may not exist
+		log.Debugf("cleanup: no gateway found: %v", err)
+		return nil
+	}
+
+	if err := gateway.DeletePortMapping(ctx, s.Protocol, int(s.InternalPort)); err != nil {
+		return fmt.Errorf("delete port mapping: %w", err)
+	}
+
+	return nil
+}