package backtrace

import (
	"net"

	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv4"
)

func newPacketV4(id uint16, dst net.IP, ttl int) []byte {
	// TODO: reuse buffers...
	msg := icmp.Message{
		Type: ipv4.ICMPTypeEcho,
		Body: &icmp.Echo{
			ID:  int(id),
			Seq: int(id),
		},
	}
	p, _ := msg.Marshal(nil)
	ip := &ipv4.Header{
		Version:  ipv4.Version,
		Len:      ipv4.HeaderLen,
		TotalLen: ipv4.HeaderLen + len(p),
		TOS:      16,
		ID:       int(id),
		Dst:      dst,
		Protocol: ProtocolICMP,
		TTL:      ttl,
	}
	buf, err := ip.Marshal()
	if err != nil {
		return nil
	}
	return append(buf, p...)
}