Add network_[type/is_expensive/is_constrained] rule items

route/rule/rule_item_network_is_constrained.go

@@ -0,0 +1,29 @@
+package rule
+
+import (
+	"github.com/sagernet/sing-box/adapter"
+)
+
+var _ RuleItem = (*NetworkIsConstrainedItem)(nil)
+
+type NetworkIsConstrainedItem struct {
+	networkManager adapter.NetworkManager
+}
+
+func NewNetworkIsConstrainedItem(networkManager adapter.NetworkManager) *NetworkIsConstrainedItem {
+	return &NetworkIsConstrainedItem{
+		networkManager: networkManager,
+	}
+}
+
+func (r *NetworkIsConstrainedItem) Match(metadata *adapter.InboundContext) bool {
+	networkInterface := r.networkManager.DefaultNetworkInterface()
+	if networkInterface == nil {
+		return false
+	}
+	return networkInterface.Constrained
+}
+
+func (r *NetworkIsConstrainedItem) String() string {
+	return "network_is_expensive=true"
+}