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package main
import (
"github.com/akrennmair/gopcap"
"log"
"net"
)
const (
TYPE_IP = 0x0800
TYPE_ARP = 0x0806
TYPE_IP6 = 0x86DD
IP_ICMP = 1
IP_INIP = 4
IP_TCP = 6
IP_UDP = 17
)
var lastIPs []string
var ipptr int
func StartListeningForPings(device, anycastIP string, snaplen int) {
lastIPs = make([]string, 255)
ipptr = 0
var incomingIP net.IP = net.ParseIP(anycastIP)
if incomingIP == nil || anycastIP == "1.2.3.4" {
log.Fatal("Incorrect Anycast IP given")
}
if device == "" {
devs, err := pcap.Findalldevs()
if err != nil {
log.Fatal("tcpdump: couldn't find any devices: %s\n", err)
}
if 0 == len(devs) {
log.Fatal("tcpdump: Device error, RTFM please")
}
device = devs[0].Name
}
h, err := pcap.Openlive(device, int32(snaplen), true, 0)
if h == nil {
log.Fatal("tcpdump: %s\n", err)
return
}
defer h.Close()
// if expr != "" {
// ferr := h.Setfilter(expr)
// if ferr != nil {
// log.Fatal("tcpdump: %s\n", ferr)
// out.Flush()
// }
// }
for pkt := h.Next(); pkt != nil; pkt = h.Next() {
pkt.Decode()
if pkt.IP != nil {
if pkt.IP.Protocol == 1 && pkt.IP.DestAddr() == incomingIP.String() {
// type Icmphdr struct {
// Type uint8
// Code uint8
// Checksum uint16
// Id uint16
// Seq uint16
// Data []byte
// }
for level, headerr := range pkt.Headers {
switch header := headerr.(type) {
case *pcap.Icmphdr:
if header.Type == 0 {
log.Printf("What(%d) ICMP! %s %d %d %d %d %d '%x'", level, pkt.IP.SrcAddr(), header.Type, header.Code, header.Checksum, header.Id, header.Seq, pkt.Payload)
LogPing(string(pkt.Payload))
}
case *pcap.Iphdr:
//log.Printf("What(%d) ICMP! %d %d %d %d %d", level, header.Type, header.Code, header.Checksum, header.Id, header.Seq)
default:
log.Printf("Ahem %s ", header)
}
}
}
}
}
}
func min(a, b int) int {
if a < b {
return a
}
return b
}
func LogPing(ip string) {
if ipptr+1 > len(lastIPs) {
ipptr = 0
}
lastIPs[ipptr] = ip
ipptr++
}