sniffer.c

#include <pcap.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/if_ether.h>

void callback(u_char *args, const struct pcap_pkthdr* pkthdr, const u_char* packet)

{
	int i = 0;
	static int count = 0;

	printf("Packet Count: %d\n", ++count);
	printf("Recieved Packet size : %d\n", pkthdr->len);
	printf("Payload:\n");
	for (i =0; i<pkthdr->len; i++)
	{
		if (isprint(packet[i]))
			printf("%c ", packet[i]);
		else
			printf(" . ");
		if((i%16==0 && i!=0)|| i == pkthdr->len-1)
			printf("\n");
	}

}

int main(int argc, char **argv)
{
	int i;
	char *dev;
	char errbuf[PCAP_ERRBUF_SIZE];
	pcap_t* descr;
	const u_char *packet;
	struct pcap_pkthdr hdr;
	struct ether_header *eptr;
	struct bpf_program fp;
	bpf_u_int32 maskp;
	bpf_u_int32 netp;

if(argc != 2)
	{
		fprintf(stdout, "Usage: %s \"expression\"\n", argv[0]);
		return 0;
	}

/*Get a device*/

	dev = pcap_lookupdev(errbuf);
if (dev == NULL)
	{	
	 fprintf(stderr, "%s\n",errbuf);
	 exit(1);
		
	}
/*Get network addr and mask*/

	pcap_lookupnet(dev, &netp, &maskp, errbuf);

	descr = pcap_open_live(dev, BUFSIZ, 1, -1, errbuf);
	
if(descr == NULL)
	{
	printf("pcap_open_live():%s\n", errbuf);
	exit(1);	
	
	}	
if(pcap_compile(descr,&fp, argv[1], 0, netp) == -1)
	{
	fprintf(stderr, "Error calling pcap_compile\n");
	exit(1);	
	}

if(pcap_setfilter(descr,&fp) == -1)
	{
	fprintf(stderr, "Error setting filter!\n");
	exit(1);
	}
	
	pcap_loop(descr,-1, callback, NULL);
	return 0;
}