/**
 * Helper to build an IP header given the source host address (sha), target
 * host address (tha), and the desired TTL. The header is created where
 * iphdr points to.
 */
void
buildIpHeader(struct iphdr * iphdr, struct in_addr * sha, struct in_addr * tha,
        u_int8_t ttl) {
    /* ==================================================================== *
     * YOUR TASK                                                            *
     * Build an IP Header                                                   *
     * ==================================================================== */

     iphdr->version = 4;
     iphdr->ihl = 5;
     iphdr->tos = 0;

     iphdr->tot_len = htons(28);
     iphdr->id = htons(rand());
     iphdr->frag_off = htons(0);

     iphdr->ttl = ttl;
     iphdr->protocol = IPPROTO_ICMP;

     iphdr->saddr = sha->s_addr;
     iphdr->daddr = tha->s_addr;

     iphdr->check = in_cksum( (u_int16_t *)iphdr, sizeof(struct iphdr));

    /* TASK END.
     * ==================================================================== */
}


/**
 * Helper to create an ICMP Echo Request (type 8, code 0) whith given Id
 * and sequence number. The header is created where icmphdr points to.
 */
void
buildIcmpEchoRequest(struct icmphdr * icmphdr, u_int16_t id, u_int16_t seq) {
    /* ==================================================================== *
     * YOUR TASK                                                            *
     * Build an ICMP Echo Request Header.                                   *
     * ==================================================================== */

     icmphdr->type = 8;
     icmphdr->code = 0;
     icmphdr->un.echo.id = htons(id);
     icmphdr->un.echo.sequence = htons(seq);

     icmphdr->checksum = in_cksum((u_int16_t *)icmphdr, sizeof(struct icmphdr));

    /* TASK END.
     * ==================================================================== */
}