#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#include <linux/ip.h>
#include <linux/udp.h>

unsigned short csum (unsigned short *buf, int nwords)
{
	unsigned long sum;
	for (sum = 0; nwords > 0; nwords--)
		sum += *buf++;
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	
	return ~sum;
}

int main (int argc, char** argv)
{
	char datagram[4096];
	struct sockaddr_in sin;

	int fd = socket (PF_INET, SOCK_RAW, IPPROTO_UDP);

	struct iphdr *iph = (struct iphdr *) datagram;
	struct udphdr *udph = (struct udphdr *) datagram + sizeof (struct iphdr);

	sin.sin_family = AF_INET;
	sin.sin_port = htons (5070);
	sin.sin_addr.s_addr = inet_addr ("213.248.63.122");

	memset (datagram, 0, 4096);

	iph->ihl = 5;
	iph->version = 4;
	iph->tos = 0;
	iph->tot_len = sizeof (struct iphdr) + sizeof (struct udphdr);	/* no payload */
	iph->id = htonl (54321);	/* the value doesn't matter here */
	iph->frag_off = 0;
	iph->ttl = 255;
	iph->protocol = 6;
	iph->check = 0;		/* set it to 0 before computing the actual checksum later */
	iph->saddr = inet_addr ("192.168.0.1");/* SYN's can be blindly spoofed */
	iph->daddr = sin.sin_addr.s_addr;

	udph->source = htonl (1234);
	udph->dest = htonl (5070);
	udph->len = sizeof (struct udphdr); /* no payload curently */
	udph->check = 0; /* system IP stack will do the job */

	iph->check = csum ((unsigned short *) datagram, iph->tot_len >> 1);

	int one = 1;
	const int *val = &one;
	if (setsockopt (fd, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)
		printf ("Warning: Cannot set HDRINCL!\n");

	if (sendto (fd, datagram, iph->tot_len, 0, (struct sockaddr *) &sin, sizeof (sin)) < 0)
		printf ("error\n");
	else
		printf ("Success.");

	return 0;
}