Add ping proxy support

route_mapping.go

@@ -0,0 +1,45 @@
+package tun
+
+import (
+	"net/netip"
+	"time"
+
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/contrab/freelru"
+	"github.com/sagernet/sing/contrab/maphash"
+)
+
+type DirectRouteSession struct {
+	// IPVersion uint8
+	// Network     uint8
+	Source      netip.Addr
+	Destination netip.Addr
+}
+
+type RouteMapping struct {
+	status freelru.Cache[DirectRouteSession, DirectRouteDestination]
+}
+
+func NewRouteMapping(timeout time.Duration) *RouteMapping {
+	status := common.Must1(freelru.NewSharded[DirectRouteSession, DirectRouteDestination](1024, maphash.NewHasher[DirectRouteSession]().Hash32))
+	status.SetOnEvict(func(session DirectRouteSession, action DirectRouteDestination) {
+		action.Close()
+	})
+	status.SetLifetime(timeout)
+	return &RouteMapping{status}
+}
+
+func (m *RouteMapping) Lookup(session DirectRouteSession, constructor func() (DirectRouteDestination, error)) (DirectRouteDestination, error) {
+	var (
+		created DirectRouteDestination
+		err     error
+	)
+	action, _, ok := m.status.GetAndRefreshOrAdd(session, func() (DirectRouteDestination, bool) {
+		created, err = constructor()
+		return created, err != nil
+	})
+	if !ok {
+		return created, err
+	}
+	return action, nil
+}