//go:build linux && !android && !e2e_testing
// +build linux,!android,!e2e_testing

package tio

import (
	"fmt"

	"golang.org/x/sys/unix"

	"github.com/slackhq/nebula/overlay/tio/virtio"
)

// protoFromGSOType maps a virtio_net_hdr GSOType to the GSOProto value the
// segment-time helpers use. Returns an error for GSO_NONE or any unknown
// value — the caller should only invoke this on a confirmed superpacket.
func protoFromGSOType(t uint8) (GSOProto, error) {
	switch t {
	case unix.VIRTIO_NET_HDR_GSO_TCPV4, unix.VIRTIO_NET_HDR_GSO_TCPV6:
		return GSOProtoTCP, nil
	case unix.VIRTIO_NET_HDR_GSO_UDP_L4:
		return GSOProtoUDP, nil
	default:
		return 0, fmt.Errorf("unsupported virtio gso type: %d", t)
	}
}

// SegmentSuperpacket invokes fn once per segment of pkt. For non-GSO pkts
// fn is called once with pkt.Bytes (no segmentation, no copy). For GSO/USO
// superpackets fn is called once per segment with a slice of pkt.Bytes
// holding that segment's plaintext (a freshly-patched L3+L4 header sliced
// in front of the original payload chunk). The slide is destructive: pkt is
// consumed by this call and its bytes are in an undefined state when
// SegmentSuperpacket returns. Callers must not retain pkt or any earlier
// seg slice past fn's return for that segment. The scratch parameter is
// unused on the destructive path and kept only for cross-platform
// signature compatibility. Aborts and returns the first error from fn or
// from per-segment construction.
func SegmentSuperpacket(pkt Packet, fn func(seg []byte) error) error {
	if !pkt.GSO.IsSuperpacket() {
		return fn(pkt.Bytes)
	}
	switch pkt.GSO.Proto {
	case GSOProtoTCP:
		return virtio.SegmentTCP(pkt.Bytes, pkt.GSO.HdrLen, pkt.GSO.CsumStart, pkt.GSO.Size, fn)
	case GSOProtoUDP:
		return virtio.SegmentUDP(pkt.Bytes, pkt.GSO.HdrLen, pkt.GSO.CsumStart, pkt.GSO.Size, fn)
	default:
		return fmt.Errorf("unsupported gso proto: %d", pkt.GSO.Proto)
	}
}