/*-----------------------------------------------------------------------------
* Method: void makeip(struct ip* ipHdr, unsigned int len, unsigned char ttl,
* unsigned char proto, in_addr* src, in_addr* dst)
*
* makes an ip header out of the given info, assumes everything is in host
* byte order
*---------------------------------------------------------------------------*/
void makeip(
struct ip* ipHdr,
unsigned int len,
uint16_t off,
unsigned char ttl,
unsigned char proto,
uint32_t src,
uint32_t dst )
{
uint32_t sbuf, dbuf;
uint8_t* p = (uint8_t*) ipHdr;
*p = 0x45; // set ip version and header length
ipHdr->ip_tos = 0;
ipHdr->ip_len = htons(len);
ipHdr->ip_id = 0; // what should this be?
ipHdr->ip_off = htons(off);
ipHdr->ip_ttl = ttl;
ipHdr->ip_p = proto;
// read into buffers in case we are overwriting in place
sbuf = src;
dbuf = dst;
ipHdr->ip_src.s_addr = sbuf;
ipHdr->ip_dst.s_addr = dbuf;
ipHdr->ip_sum = 0x0000;
ipHdr->ip_sum = in_checksum((uint16_t*)ipHdr, 20);
}
int do_checksum(u_char *buf, int protocol, int len)
/* len = protocol header length + payload length */
{
struct ip *ip;
int iplen, sum = 0;
if (len == 0) {
fprintf(stderr, "header length can't be zero");
return -1;
}
ip = (struct ip *)buf;
if (ip->ip_v != 4) {
fprintf(stderr, "Unsupported IP protocol: %d", ip->ip_v);
return -1;
}
iplen = ip->ip_hl << 2;
switch (protocol) {
case IPPROTO_TCP:
{
struct tcphdr *tcp = (struct tcphdr *)(buf + iplen);
tcp->th_sum = 0;
sum = in_checksum((uint16_t *)&ip->ip_src, 8);
sum += ntohs(IPPROTO_TCP+len);
sum += in_checksum((uint16_t *)tcp, len);
tcp->th_sum = CKSUM_CARRY(sum);
break;
}
case IPPROTO_UDP:
{
struct udphdr *udp = (struct udphdr *)(buf + iplen);
udp->uh_sum = 0;
sum = in_checksum((uint16_t *)&ip->ip_src, 8);
sum += ntohs(IPPROTO_UDP+len);
sum += in_checksum((uint16_t *)udp, len);
udp->uh_sum = CKSUM_CARRY(sum);
break;
}
case IPPROTO_ICMP:
{
struct icmp *icmp = (struct icmp *)(buf + iplen);
icmp->icmp_cksum = 0;
sum = in_checksum((uint16_t *)icmp, len);
icmp->icmp_cksum = CKSUM_CARRY(sum);
break;
}
case IPPROTO_IP:
{
ip->ip_sum = 0;
sum = in_checksum((uint16_t *)ip, ip->ip_hl);
ip->ip_sum = CKSUM_CARRY(sum);
break;
}
default:
{
fprintf(stderr, "Unsupported protocol: %d", protocol);
return -1;
}
}
#ifdef _DEBUG
printf("\nProtocol: %d: %x\n", protocol, CKSUM_CARRY(sum));
#endif
return 0;
}
int main(int argc, char** argv) {
if(argc < 2) {
std::cerr << "Specify destination ip address" << std::endl;
exit(EXIT_FAILURE);
}
std::string dest_addr = argv[1];
uint32_t my_time = get_time();
icmp_timestamp_mgs msg;
msg.hdr.type = ICMP_TIMESTAMP;
msg.hdr.code = 0;
msg.hdr.checksum = 0;
msg.hdr.un.echo.id = 0;
msg.hdr.un.echo.sequence = 0;
msg.originate = htonl(my_time);
msg.receive = 0;
msg.transmit = 0;
msg.hdr.checksum = in_checksum((uint16_t*)&msg, sizeof(msg));
int sockfd;
if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
sockaddr_in dest;
dest.sin_family = AF_INET;
dest.sin_addr.s_addr = inet_addr(dest_addr.c_str());
int send_cnt = sendto(sockfd, &msg, sizeof(msg), 0, (sockaddr*)&dest, sizeof(sockaddr));
if(send_cnt == -1) {
perror("send");
exit(EXIT_FAILURE);
}
if(send_cnt != sizeof(msg)) {
fprintf(stderr, "failed to send full packet\n");
exit(EXIT_FAILURE);
}
// set timeout
timeval tv;
tv.tv_sec = 5;
tv.tv_usec = 0;
setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
char buffer[sizeof(iphdr) + sizeof(icmp_timestamp_mgs)];
socklen_t addrlen = sizeof(dest);
int recv_cnt = recvfrom(sockfd, &buffer, sizeof(buffer), 0, (sockaddr*)&dest, &addrlen);
uint32_t receive_time = get_time();
if(recv_cnt == -1) {
perror("recv");
exit(EXIT_FAILURE);
}
if(recv_cnt != sizeof(buffer)) {
fprintf(stderr, "failed to receive full packet\n");
exit(EXIT_FAILURE);
}
icmp_timestamp_mgs &answer = *(icmp_timestamp_mgs*)(buffer + sizeof(iphdr));
if(answer.hdr.type != ICMP_TIMESTAMPREPLY) {
fprintf(stderr, "received wrong message\n");
exit(EXIT_FAILURE);
}
int64_t delta = calc_delta(answer, receive_time);
std::cout << "Time delta: " << delta / 1000 << "s " << abs(delta) % 1000 << "ms" << std::endl;
close(sockfd);
return 0;
}
