Add flow dispatcher

flow.go

@@ -0,0 +1,32 @@
+package tun
+
+import "net/netip"
+
+type FlowVerdict struct {
+	Action      FlowAction
+	Port        Port
+	Destination netip.AddrPort
+}
+
+type FlowAction uint8
+
+const (
+	ActionAccept FlowAction = iota
+	ActionFlow
+	ActionReject
+	ActionDrop
+	ActionBypass
+)
+
+type Port interface {
+	PortAddresses() (v4 netip.Addr, v6 netip.Addr)
+	PortMTU() uint32
+	AttachReturn(returnPath Return) error
+	DetachReturn(returnPath Return) error
+	WritePackets(packets [][]byte) error
+}
+
+type Return interface {
+	ReturnHeadroom() int
+	ReturnPackets(packets [][]byte) [][]byte
+}