tun

type Config struct {
	// Engine is the ICX engine performing encap/decap + crypto. *icx.Handler
	// satisfies this; it must be configured in layer3 mode (WithLayer3VirtFrames),
	// since the TUN device carries raw L3 inner packets.
	Engine vtep.EngineXfrm
	// Device is the overlay-side TUN device. The driver owns it and closes it on
	// Close.
	Device Device
	// Underlay is the encap'd-frame transport. The driver owns it and closes it on
	// Close.
	Underlay Underlay
	// DeviceOffset is the read/write headroom offset into Device buffers. The real
	// wireguard TUN needs >= virtioNetHdrLen (10); device_linux.go uses 16. The
	// test fake uses 0. Negative values are treated as 0.
	DeviceOffset int
	// InnerMTU is the overlay MTU; 0 uses defaultInnerMTU (1280). It sizes the TUN
	// read/decap buffers and must not exceed what the underlay path can carry.
	InnerMTU int
	// FlushInterval overrides how often scheduled (keep-alive) frames are flushed.
	// Zero uses defaultFlushInterval.
	FlushInterval time.Duration
}

type Datapath struct {
	// contains filtered or unexported fields
}

type Device interface {
	// Read reads up to len(bufs) packets, writing packet i into bufs[i][offset:]
	// and its length into sizes[i] (len(sizes) >= len(bufs)); returns the packet
	// count. It blocks until at least one packet is available or the device is
	// closed (after which it returns a closed error).
	Read(bufs [][]byte, sizes []int, offset int) (int, error)
	// Write writes len(bufs) packets, taking packet i from bufs[i][offset:].
	Write(bufs [][]byte, offset int) (int, error)
	// BatchSize is the max number of packets a single Read/Write handles.
	BatchSize() int
	io.Closer
}

type OpenConfig struct {
	// Engine is the ICX engine; it must be configured in layer3 mode.
	Engine vtep.EngineXfrm
	// Name is the TUN interface name to create (e.g. "icx0"). An empty name lets
	// the kernel pick one.
	Name string
	// OverlayAddrs are the L3 addresses assigned to the TUN device (the overlay
	// CIDRs the consumer's stack owns).
	OverlayAddrs []netip.Prefix
	// Routes are the overlay prefixes routed out the TUN device (link-scoped).
	Routes []netip.Prefix
	// InnerMTU is the device MTU / inner-MTU clamp; 0 uses defaultInnerMTU (1280).
	InnerMTU int
	// UnderlayBind is the local UDP address the underlay socket binds to.
	UnderlayBind netip.AddrPort
	// FlushInterval overrides the keep-alive flush cadence; 0 uses the default.
	FlushInterval time.Duration
}

type Underlay interface {
	// ReadFrame reads a single underlay frame into buf, returning its length. A
	// length of 0 with a nil error is skipped. Once Close has been called it must
	// return an error satisfying errors.Is(err, net.ErrClosed).
	ReadFrame(buf []byte) (int, error)
	// WriteFrames writes a batch of full phy frames, returning the number actually
	// sent. A short write (n < len(frames)) is permitted; the datapath drains the
	// unsent suffix by calling again, so implementations must not drop the tail. A
	// zero return with a nil error is treated as a stall. The frames are owned by
	// the caller and valid only until the call returns.
	WriteFrames(frames [][]byte) (int, error)
	io.Closer
}