/* gcc src.c -lpcap */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <pcap/pcap.h>
#include <netinet/ether.h>
#include <netinet/ip.h>

struct byte {
        unsigned int a:1;
        unsigned int b:1;
        unsigned int c:1;
        unsigned int d:1;
        unsigned int e:1;
        unsigned int f:1;
        unsigned int g:1;
        unsigned int h:1;
};

void showbin(char *buf, int len)
{
        int i,j;
        char ch;
        struct byte *ba;

        for(i=0; i<len; i++) {
                ch = *(buf+i);
        	ba = (struct byte *)&ch;
		printf("%d%d%d%d", (*ba).h, (*ba).g, (*ba).f, (*ba).e);
		printf("%d%d%d%d", (*ba).d, (*ba).c, (*ba).b, (*ba).a);
		printf(" ");
        }
}

void show_packet_bin(char *buf, int len)
{
	unsigned char ch;
	int i, j, k, space;

	for (i = 0; i < len; i+=16) {
		printf("\t0x%04x  ", i);
		for (j = i; j < i+16 && j < len; j++) {
			ch = (unsigned char)buf[j];
			printf("%02X       ", ch);
		}
 
		if (j == i+16)
			space = 1;
		else
			space = 1 + (16*9) - (j-i)*9;
 
		for (k = 0; k < space; k++)
			printf(" ");
 
		for (j = i; j < i+16 && j < len; j++) {
			ch = (unsigned char)buf[j];
			if (ch <= 32 || ch >= 127)
				ch = '.';
			printf("%c", ch);
		}
		printf("\n");

		printf("\t        ");
		for (j = i; j < i+16 && j < len; j++)
			showbin(&buf[j],1);
		printf("\n");

	}
	printf("\n");
}

char *ether_ntoa_padded(const struct ether_addr *addr, char *buf)
{
	sprintf (buf, "%02x:%02x:%02x:%02x:%02x:%02x",
		addr->ether_addr_octet[0], addr->ether_addr_octet[1],
		addr->ether_addr_octet[2], addr->ether_addr_octet[3],
		addr->ether_addr_octet[4], addr->ether_addr_octet[5]);
	return buf;
}

void show_ethernet_header(char *packet, int len)
{
	/* man 3 ether_aton */
	/* /usr/include/linux/if_ether.h */

	struct ethhdr *h;
	h = (struct ethhdr *)packet;

	struct ether_addr *dst;
	dst = (struct ether_addr *)(h->h_dest);

	struct ether_addr *src;
	src = (struct ether_addr *)(h->h_source);
	
	char addr_str[INET6_ADDRSTRLEN];
	printf("Ethernet header info:\n");
	printf("\tdst: %s (%s)\n", ether_ntoa(dst), ether_ntoa_padded(dst, addr_str));
	printf("\tsrc: %s (%s)\n", ether_ntoa(src), ether_ntoa_padded(src, addr_str));
	printf("\ttype: 0x%04X\n", ntohs(h->h_proto));
	printf("\n");
}

void show_endianness()
{
	#if __BYTE_ORDER == __LITTLE_ENDIAN
		printf("Endianness : Little Endian\n");
	#elif __BYTE_ORDER == __BIG_ENDIAN
		printf("Endianness : Big Endian\n");
	#else
		printf("Endianness : Unknown\n");
	#endif
	printf("\n");
}

void show_ip_header(char *packet, int len)
{
	/* /usr/include/netinet/ip.h */

	struct ip *h;
	h = (struct ip *)(packet + sizeof(struct ethhdr));

	printf("IP header info:\n");

	printf("\tver   : %X\n",h->ip_v);
	printf("\tihl   : %X\n", h->ip_hl);
	printf("\ttos   : 0x%X\n", h->ip_tos);
	printf("\tlen   : %u\n", ntohs(h->ip_len));
	printf("\tid    : %u\n", ntohs(h->ip_id));

	printf("\tfrag : %X ", ntohs(h->ip_off));
	if(ntohs(h->ip_off) == 0x4000)
		printf("(DF)");
	if(ntohs(h->ip_off) == 0x2000)
		printf("(MF)");
	printf("\n");

	printf("\tttl   : %u\n", h->ip_ttl);
	printf("\tproto : %u\n", h->ip_p);
	printf("\tsum   : 0x%X\n", ntohs(h->ip_sum));

	char ipv4str[INET_ADDRSTRLEN];

	inet_ntop(AF_INET, &h->ip_src, ipv4str, INET_ADDRSTRLEN);
	printf("\tsaddr : %X (%s)\n", ntohl(*(uint32_t *)(&h->ip_src)), ipv4str);

	inet_ntop(AF_INET, &h->ip_dst, ipv4str, INET_ADDRSTRLEN);
	printf("\tdaddr : %X (%s)\n", ntohl(*(uint32_t *)(&h->ip_dst)), ipv4str);

	printf("\n");

}

void packet_handler(u_char *user, const struct pcap_pkthdr *h, const u_char *bytes)
{
	static int packet_count = 0;
	for (int i = 0;i < 80; i++) putchar('#');
	printf("\n# Packet: %d , Size: %d\n\n", ++packet_count, h->len);
	show_packet_bin((char *)bytes, h->len);
	show_endianness();
	show_ethernet_header((char *)bytes, h->len);
	show_ip_header((char *)bytes, h->len);
}

int main()
{
	pcap_t *p;
	char errbuf[PCAP_ERRBUF_SIZE];
	p = pcap_open_offline("capture.pcap", errbuf);
	if (p == NULL) {
		fprintf(stderr, "\npcap_open_offline() failed: %s\n", errbuf);
		exit(EXIT_FAILURE);
	}

	if (pcap_loop(p, 0, packet_handler, NULL) < 0) {
		fprintf(stderr, "\npcap_loop() failed: %s\n", pcap_geterr(p));
		exit(EXIT_FAILURE);
	}

	return 0;
}