// commande : sudo ./send_eth <ifname> <dst-mac> <src-mac> <ethertype(hex)> <payload-as-string>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>
#include <linux/if.h>

static int mac_from_str(const char *s, unsigned char *mac) {
    int vals[6];
    if (sscanf(s, "%x:%x:%x:%x:%x:%x",
               &vals[0], &vals[1], &vals[2],
               &vals[3], &vals[4], &vals[5]) != 6) return -1;
    for (int i = 0; i < 6; ++i) mac[i] = (unsigned char)vals[i];
    return 0;
}

int main(int argc, char **argv) {
    if (argc < 6) {
        fprintf(stderr, "Usage: %s <ifname> <dst-mac> <src-mac> <ethertype(hex)> <payload>\n", argv[0]);
        return 1;
    }

    const char *ifname = argv[1];
    unsigned char dst_mac[6], src_mac[6];
    if (mac_from_str(argv[2], dst_mac) < 0) { fprintf(stderr, "Bad dst-mac\n"); return 1; }
    if (mac_from_str(argv[3], src_mac) < 0) { fprintf(stderr, "Bad src-mac\n"); return 1; }

    unsigned int ethertype;
    if (sscanf(argv[4], "%x", &ethertype) != 1) { fprintf(stderr, "Bad ethertype\n"); return 1; }

    const char *payload = argv[5];
    size_t payload_len = strlen(payload);

    int sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    if (sock == -1) { perror("socket"); return 1; }

    struct ifreq ifr;
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);
    if (ioctl(sock, SIOCGIFINDEX, &ifr) == -1) { perror("SIOCGIFINDEX"); close(sock); return 1; }
    int ifindex = ifr.ifr_ifindex;

    unsigned char frame[ETH_FRAME_LEN];
    size_t frame_len = 0;

    memcpy(frame + frame_len, dst_mac, 6); frame_len += 6;
    memcpy(frame + frame_len, src_mac, 6); frame_len += 6;
    frame[frame_len++] = (ethertype >> 8) & 0xff;
    frame[frame_len++] = ethertype & 0xff;

    if (payload_len + frame_len > ETH_DATA_LEN + ETH_HLEN) {
        fprintf(stderr, "Payload too large\n"); close(sock); return 1;
    }
    memcpy(frame + frame_len, payload, payload_len);
    frame_len += payload_len;

    if (frame_len < 60) {
        memset(frame + frame_len, 0, 60 - frame_len);
        frame_len = 60;
    }

    struct sockaddr_ll sock_addr;
    memset(&sock_addr, 0, sizeof(sock_addr));
    sock_addr.sll_ifindex = ifindex;
    sock_addr.sll_halen = ETH_ALEN;
    memcpy(sock_addr.sll_addr, dst_mac, 6);

    ssize_t sent = sendto(sock, frame, frame_len, 0, (struct sockaddr*)&sock_addr, sizeof(sock_addr));
    if (sent == -1) { perror("sendto"); close(sock); return 1; }

    printf("Sent %zd bytes on %s\n", sent, ifname);
    close(sock);
    return 0;
}