#include <stdio.h>
#include <iostream>
#include <pcap.h>

// Initalize variables.

using namespace std;

pcap_t *handle;                 /* Session handle */
string dev;             /* Device to sniff on */
char errbuf[PCAP_ERRBUF_SIZE];  /* Error string */
struct bpf_program fp;          /* The compiled filter expression */
char filter_exp[] = "port 23";	/* The filter expression */
bpf_u_int32 mask;               /* The netmask of our sniffing device */
bpf_u_int32 net;                /* The IP of our sniffing device */

int main()
{
	char *dev, errbuf[PCAP_ERRBUF_SIZE];

    dev = pcap_lookupdev(errbuf);
	
    if (dev == NULL) {
		fprintf(stderr, "Couldn't find default device: %s\n", errbuf);
		return(2);
	}
    
    if(pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
        fprintf(stderr, "Can't get netmask for device %s\n", dev);
        net = 0;
        mask = 0;
    }

    handle = pcap_open_live(dev, BUFSIZ, 1, 1000, errbuf);

    if(handle == NULL) {
        fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);
        return(2);
    }

    if(pcap_compile(handle, &fp, filter_exp, 0, net) == -1) {
        fprintf(stderr, "Couldn't parse filter %s: %s\n", filter_exp, pcap_geterr(handle));
        return(2);
    }

    if(pcap_setfilter(handle, &fp) == -1) {
        fprintf(stderr, "Couldn't install filter %s: %s\n", filter_exp, pcap_geterr(handle));
        return(2);
    }
}