/***************SimpelSniffer.c*************/

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#define BUFFER_MAX 2048


int main(int argc, char *argv[])
{
    
    int sock, n_read, proto;    
    char buffer[BUFFER_MAX];
    char *ethhead, *iphead, *tcphead, *udphead, *icmphead, *p;
    
    if((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP))) < 0)
    {
        fprintf(stdout, "create socket error\n");
        exit(0);
    }
    while(1) 
    {
        n_read = recvfrom(sock, buffer, 2048, 0, NULL, NULL);
        /*
        14   6(dest)+6(source)+2(type or length)
        +
        20   ip header 
        +
        8    icmp,tcp or udp header
        = 42
        */
        if(n_read < 42) 
        {
            fprintf(stdout, "Incomplete header, packet corrupt\n");
            continue;
        }
        
        ethhead = buffer;
        p = ethhead;
        int n = 0XFF;
        printf("MAC: %.2X:%02X:%02X:%02X:%02X:%02X==>"
            "%.2X:%.2X:%.2X:%.2X:%.2X:%.2X\n",
            p[6]&n, p[7]&n, p[8]&n, p[9]&n, p[10]&n, p[11]&n,
            p[0]&n, p[1]&n, p[2]&n, p[3]&n, p[4]&n, p[5]&n);


        iphead = ethhead + 14;  
        p = iphead + 12;
        
        printf("IP: %d.%d.%d.%d => %d.%d.%d.%d\n",
            p[0]&0XFF, p[1]&0XFF, p[2]&0XFF, p[3]&0XFF,
            p[4]&0XFF, p[5]&0XFF, p[6]&0XFF, p[7]&0XFF);
        
        proto = *(iphead + 9);

        p = iphead + 20;
        printf("Protocol: ");
        switch(proto)
        {
        case IPPROTO_ICMP: printf("ICMP\n");break;
        case IPPROTO_IGMP: printf("IGMP\n");break;
        case IPPROTO_IPIP: printf("IPIP\n");break;
        case IPPROTO_TCP :
        case IPPROTO_UDP : printf("%s,", proto == IPPROTO_TCP ? "TCP": "UDP"); 
            printf("source port: %u,",(p[0]<<8)&0XFF00 |  p[1]&0XFF);
            printf("dest port: %u\n", (p[2]<<8)&0XFF00 | p[3]&0XFF);
            break;
        case IPPROTO_RAW : printf("RAW\n");break;
        default:printf("Unkown, please query in include/linux/in.h\n");
        }
    }
}