Packet capture

capture.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>

int main(int argc, char **argv)
{
    int sockfd;
    struct ifreq if_info;
    int ifindex;
    struct sockaddr_ll lladdr = { 0 };
    int i;
    char packetbuf[1500];

    memset(&if_info, 0, sizeof(if_info));

    if (argc < 2)
    {
        fprintf(stderr, "Usage: %s if-name\n", argv[0]);
        return 1;
    }

    sockfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    if (sockfd < 0)
    {
        perror("socket() failed");
        return 1;
    }

    strncpy(if_info.ifr_name, argv[1], IFNAMSIZ);
    if (ioctl(sockfd, SIOCGIFINDEX, &if_info))
    {
        perror("ioctl(SIOCGIFINDEX) failed");
        close(sockfd);
        return 1;
    }
    ifindex = if_info.ifr_ifindex;
    printf("%s index = %d\n", if_info.ifr_name, ifindex);

    lladdr.sll_family = AF_PACKET;
    lladdr.sll_ifindex = ifindex;

    if (bind(sockfd, (struct sockaddr*)&lladdr, sizeof(lladdr)))
    {
        perror("bind() failed");
        close(sockfd);
        return 0;
    }

    for (i = 0; i < 10; ++i)
    {
        ssize_t bytes_read = read(sockfd, packetbuf, sizeof(packetbuf));
        if (bytes_read < 0)
        {
            perror("read() failed");
            break;
        }
        printf("Receieved packet len = %d\n", (int)bytes_read);
    }

    close(sockfd);

    return 0;
}