#include "rtcp.h"

#ifndef __FAVOR_BSD
#define __FAVOR_BSD
#endif

#ifndef __USE_BSD
#define __USE_BSD
#endif

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

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <libnetfilter_queue/libnetfilter_queue.h>
#include <linux/netfilter.h>

static int bounce(struct nfq_q_handle *q, struct nfgenmsg *m,
                  struct nfq_data *d, void *a)
{
	int id;
	int ret;
	struct ip *ip;
	struct udphdr *udp;
	uint32_t addr;
	uint16_t port;

	(void)m;
	(void)a;

	id = ntohl((nfq_get_msg_packet_hdr(d))->packet_id);
	nfq_get_payload(d, (char **)&ip);
	udp = (struct udphdr *)((uint32_t *) ip + ip->ip_hl);

	addr = ip->ip_src.s_addr;
	ip->ip_src.s_addr = ip->ip_dst.s_addr;
	ip->ip_dst.s_addr = addr;

	port = udp->uh_sport;
	udp->uh_sport = udp->uh_dport;
	udp->uh_dport = port;
	
	ret = nfq_set_verdict(q, id, NF_ACCEPT, ntohs(ip->ip_len),
			      (unsigned char *)ip);
	if (ret < 0) {
		fputs("Error setting verdict.\n", stderr);
		exit(EXIT_FAILURE);
	}
	return ret;
}

int main(int argc, char **argv)
{
	char buf[1500];
	int fd;
	int ret;
	ssize_t size;
	struct nfq_handle *h;
	struct nfq_q_handle *q;

	(void)argc;
	(void)argv;

	h = nfq_open();
	if (!h) {
		fputs("Error opening the queue interface.\n", stderr);
		exit(EXIT_FAILURE);
	}
	/*
	 * From the netfilter mailinglist: "The entire unregistration
	 * stuff is a horrible hack, the only reason why it (still)
	 * exists is because registration of the same handler returns
	 * EEXIST instead of silently ignoring it. The best fix for now
	 * is to ignore the return value of nfq_unbind_pf()."
	 */
	nfq_unbind_pf(h, AF_INET);
	ret = nfq_bind_pf(h, AF_INET);
	if (ret < 0) {
		fputs("Error binding the queue handler.\n", stderr);
		exit(EXIT_FAILURE);
	}

	q = nfq_create_queue(h, 1, bounce, NULL);
	if (!q) {
		fputs("Error creating the incoming queue.\n", stderr);
		exit(EXIT_FAILURE);
	}
	ret = nfq_set_mode(q, NFQNL_COPY_PACKET, sizeof(buf));
	if (ret < 0) {
		fputs("Error setting up the incoming queue.\n", stderr);
		exit(EXIT_FAILURE);
	}

	fd = nfq_fd(h);
	while ((size = recv(fd, buf, sizeof(buf), 0)) > 0)
		nfq_handle_packet(h, buf, size);

	nfq_destroy_queue(q);
	nfq_close(h);
	return EXIT_SUCCESS;
}