sniffer.c

Packet sniffer program using pcap.h

 #include <pcap.h>
 #include <stdio.h>
#include<sys/time.h>


void processPacket(u_char *arg,const struct pcap_pkthdr* pkthdr,const u_char * packet)
{
int i=0, *counter=(int *)arg;
printf("\nPacket count: %d",++(*counter));
printf("\nRecived Packet size: %d",pkthdr->len);
printf("\nPayLoad:\n");
//hex_print(*packet,pkthdr->len);
///*
for(i=0;i<pkthdr->len;i++)
	{
	printf("%02x ",packet[i]);
	//if(isprint(packet[i]))
	//	printf("%c",packet[i]);
	//else
	//	printf("%d ",packet[i]);
	if((i%16==0&&i!=0)||i==pkthdr->len-1)
		printf("\n");
		
	} //*/
return  ;
}

	 int main(int argc, char *argv[])
	 {
		pcap_t *handle;			/* Session handle */
		char *dev;			/* The device to sniff on */
		char errbuf[PCAP_ERRBUF_SIZE];	/* Error string */
		struct bpf_program fp;		/* The compiled filter */
		char filter_exp[] = "port 23";	/* The filter expression */
		bpf_u_int32 mask;		/* Our netmask */
		bpf_u_int32 net;		/* Our IP */
		struct pcap_pkthdr header;	/* The header that pcap gives us */
		const u_char *packet;		/* The actual packet */
		int i=0,count=0;

		/* Define the device */
		dev = pcap_lookupdev(errbuf);
		if (dev == NULL) {
			fprintf(stderr, "Couldn't find default device: %s\n", errbuf);
			return(2);
		}
		/* Find the properties for the device */
		if (pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
			fprintf(stderr, "Couldn't get netmask for device %s: %s\n", dev, errbuf);
			net = 0;
			mask = 0;
		}
		/* Open the session in promiscuous mode */
		handle = pcap_open_live(dev, BUFSIZ, 1, 1000, errbuf);
		if (handle == NULL) {
			//fprintf(stderr, "Couldn't open device %s: %s\n", somedev, errbuf);
			return(2);
		}
//
		/* Compile and apply the filter */
	//	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);
	//	}

		/* Grab a packet */
		//packet = pcap_next(handle, &header);
		/* Print its length */
		//printf("\nJacked a packet ");
		//printf("\nTime stamp:%s",ctime(&header.ts));
		//printf("\nLength of portion present:%d",header.caplen);
		//printf("\nLength this packet (off wire):%d\n",header.len);

		/* And close the session */
		pcap_loop(handle,-1,processPacket,(u_char *)&count);

		pcap_close(handle);
		return(0);
	 }