#include <errno.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

#include <time.h>

#include <arpa/inet.h>

#include <libmnl/libmnl.h>

#include <linux/netfilter.h>

#include <linux/netfilter/nfnetlink.h>

#include <linux/types.h>

#include <linux/netfilter/nfnetlink_queue.h>

#include <libnetfilter_queue/libnetfilter_queue.h>

/* only for NFQA_CT, not needed otherwise: */

#include <linux/netfilter/nfnetlink_conntrack.h>

static struct mnl_socket *nl;

static void

nfq_send_verdict(int queue_num, uint32_t id)

{

	char buf[MNL_SOCKET_BUFFER_SIZE];

	struct nlmsghdr *nlh;

	struct nlattr *nest;

	nlh = nfq_nlmsg_put(buf, NFQNL_MSG_VERDICT, queue_num);

	nfq_nlmsg_verdict_put(nlh, id, NF_ACCEPT);

	/* example to set the connmark. First, start NFQA_CT section: */

	nest = mnl_attr_nest_start(nlh, NFQA_CT);

	/* then, add the connmark attribute: */

	mnl_attr_put_u32(nlh, CTA_MARK, htonl(42));

	/* more conntrack attributes, e.g. CTA_LABELS could be set here */

	/* end conntrack section */

	mnl_attr_nest_end(nlh, nest);

	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {

		perror("mnl_socket_send");

		exit(EXIT_FAILURE);

	}

}

static int queue_cb(const struct nlmsghdr *nlh, void *data)

{

	struct nfqnl_msg_packet_hdr *ph = NULL;

	struct nlattr *attr[NFQA_MAX+1] = {};

	uint32_t id = 0, skbinfo;

	struct nfgenmsg *nfg;

	uint16_t plen;

	if (nfq_nlmsg_parse(nlh, attr) < 0) {

		perror("problems parsing");

		return MNL_CB_ERROR;

	}

	nfg = mnl_nlmsg_get_payload(nlh);

	if (attr[NFQA_PACKET_HDR] == NULL) {

		fputs("metaheader not set\n", stderr);

		return MNL_CB_ERROR;

	}

	ph = mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);

	plen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);

	/* void *payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]); */

	skbinfo = attr[NFQA_SKB_INFO] ? ntohl(mnl_attr_get_u32(attr[NFQA_SKB_INFO])) : 0;

	if (attr[NFQA_CAP_LEN]) {

		uint32_t orig_len = ntohl(mnl_attr_get_u32(attr[NFQA_CAP_LEN]));

		if (orig_len != plen)

			printf("truncated ");

	}

	if (skbinfo & NFQA_SKB_GSO)

		printf("GSO ");

	id = ntohl(ph->packet_id);

	printf("packet received (id=%u hw=0x%04x hook=%u, payload len %u",

		id, ntohs(ph->hw_protocol), ph->hook, plen);

	/*

	 * ip/tcp checksums are not yet valid, e.g. due to GRO/GSO.

	 * The application should behave as if the checksums are correct.

	 *

	 * If these packets are later forwarded/sent out, the checksums will

	 * be corrected by kernel/hardware.

	 */

	if (skbinfo & NFQA_SKB_CSUMNOTREADY)

		printf(", checksum not ready");

	puts(")");

	nfq_send_verdict(ntohs(nfg->res_id), id);

	return MNL_CB_OK;

}

int main(int argc, char *argv[])

{

	char *buf;

	/* largest possible packet payload, plus netlink data overhead: */

	size_t sizeof_buf = 0xffff + (MNL_SOCKET_BUFFER_SIZE/2);

	struct nlmsghdr *nlh;

	int ret;

	unsigned int portid, queue_num;

	if (argc != 2) {

		printf("Usage: %s [queue_num]\n", argv[0]);

		exit(EXIT_FAILURE);

	}

	queue_num = atoi(argv[1]);

	nl = mnl_socket_open(NETLINK_NETFILTER);

	if (nl == NULL) {

		perror("mnl_socket_open");

		exit(EXIT_FAILURE);

	}

	if (mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0) {

		perror("mnl_socket_bind");

		exit(EXIT_FAILURE);

	}

	portid = mnl_socket_get_portid(nl);

	buf = malloc(sizeof_buf);

	if (!buf) {

		perror("allocate receive buffer");

		exit(EXIT_FAILURE);

	}

	nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);

	nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_BIND);

	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {

		perror("mnl_socket_send");

		exit(EXIT_FAILURE);

	}

	nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);

	nfq_nlmsg_cfg_put_params(nlh, NFQNL_COPY_PACKET, 0xffff);

	mnl_attr_put_u32(nlh, NFQA_CFG_FLAGS, htonl(NFQA_CFG_F_GSO));

	mnl_attr_put_u32(nlh, NFQA_CFG_MASK, htonl(NFQA_CFG_F_GSO));

	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {

		perror("mnl_socket_send");

		exit(EXIT_FAILURE);

	}

	/* ENOBUFS is signalled to userspace when packets were lost

	 * on kernel side.  In most cases, userspace isn't interested

	 * in this information, so turn it off.

	 */

	ret = 1;

	mnl_socket_setsockopt(nl, NETLINK_NO_ENOBUFS, &ret, sizeof(int));

	for (;;) {

		ret = mnl_socket_recvfrom(nl, buf, sizeof_buf);

		if (ret == -1) {

			perror("mnl_socket_recvfrom");

			exit(EXIT_FAILURE);

		}

		ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);

		if (ret < 0){

			perror("mnl_cb_run");

			exit(EXIT_FAILURE);

		}

	}

	mnl_socket_close(nl);

	return 0;

}