filter.go

package main

import (
	"fmt"
	"log"
	"time"

	"github.com/google/gopacket"
	"github.com/google/gopacket/pcap"
)

var (
	device       string = "ens33"
	snapshot_len int32  = 1024
	promiscuous  bool   = false
	err          error
	timeout      time.Duration = 30 * time.Second
	handle       *pcap.Handle
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	// Set filter
	var filter string = "udp"
	err = handle.SetBPFFilter(filter)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("Only capturing udp.")

	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		// Do something with a packet here.
		fmt.Println(packet)
		break
	}

}