vtep

type Datapath interface {
	// Run drives the I/O loop, blocking until shutdown, then returns. Cancelling
	// ctx stops the send path. For drivers handed an injected underlay (netstack),
	// the receive path stops only when the consumer closes that underlay, so Run
	// returns once both have happened — cancelling ctx alone may not suffice.
	// A nil return means a clean shutdown. Run must not be called more than once.
	Run(ctx context.Context) error

	// Close stops the datapath. Drivers that own their underlay/device release
	// them here; drivers handed an injected underlay leave its lifecycle to the
	// consumer. Safe to call after Run returns; Run must not be called after Close.
	io.Closer
}

type EngineXfrm interface {
	// PhyToVirt decapsulates a physical (underlay) frame into virt, returning
	// the number of bytes written, or 0 to drop.
	PhyToVirt(phy, virt []byte) int

	// VirtToPhy encapsulates a virtual (overlay) frame into phy, returning the
	// number of bytes written and whether the frame was instead handled as an
	// immediate local reply (ARP/ND) that must go back out the overlay side.
	VirtToPhy(virt, phy []byte) (int, bool)

	// ToPhy lets the engine emit a scheduled frame (e.g. a keep-alive) into
	// phy, returning the number of bytes written, or 0 when there is nothing
	// to send.
	ToPhy(phy []byte) int
}