#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <netinet/in.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/filter.h>
#include <asm/byteorder.h>

static inline int nlmsg_msg_size(int payload)
{
	return NLMSG_HDRLEN + payload;
}

static inline void *nlmsg_data(const struct nlmsghdr *nlh)
{
	return (unsigned char *) nlh + NLMSG_HDRLEN;
}

static inline int nlmsg_total_size(int payload)
{
	return NLMSG_ALIGN(nlmsg_msg_size(payload));
}

static inline int nlmsg_padlen(int payload)
{
	return nlmsg_total_size(payload) - nlmsg_msg_size(payload);
}


static struct nlmsghdr *nlmsg_put(void *buf, uint32_t pid, uint32_t seq,
				  int type, int payload, int flags)
{
	struct nlmsghdr *nlh;

	nlh = (struct nlmsghdr *) buf;
	nlh->nlmsg_type = type;
	nlh->nlmsg_len = nlmsg_msg_size(payload);
	nlh->nlmsg_flags = flags;
	nlh->nlmsg_pid = pid;
	nlh->nlmsg_seq = seq;

	memset((unsigned char *) nlmsg_data(nlh) + payload, 0,
	       nlmsg_padlen(payload));

	return nlh;
}

static int fill_info(unsigned char *buf, uint32_t pid, uint32_t seq, int event,
		     int flags, unsigned proto)
{
	struct rtmsg *r;
	struct nlmsghdr *nlh;

	nlh = nlmsg_put(buf, pid, seq, event, sizeof(*r), 0);

	r = nlmsg_data(nlh);
	r->rtm_family	 = AF_INET;
	r->rtm_dst_len	= 32;
	r->rtm_src_len	= 0;
	r->rtm_tos	= 0;
	r->rtm_table	= RT_TABLE_MAIN;
	r->rtm_type	= 0;
	r->rtm_scope	= RT_SCOPE_UNIVERSE;
	r->rtm_protocol = RTPROT_UNSPEC;
	r->rtm_flags	= flags;

	return (void *) (r+1) - (void *) buf;
}

static const char *nltypes[] = {
	[RTM_NEWROUTE] = "RTM_NEWROUTE",
	[RTM_DELROUTE] = "RTM_DELROUTE",
	[RTM_GETROUTE] = "RTM_GETROUTE",
	[RTM_NEWLINK] = "RTM_NEWLINK",
	[RTM_DELLINK] = "RTM_DELLINK",
	[RTM_GETLINK] = "RTM_GETLINK",
	[RTM_NEWADDR] = "RTM_NEWADDR",
	[RTM_DELADDR] = "RTM_DELADDR",
	[RTM_GETADDR] = "RTM_GETADDR",
};

static struct sock_filter filter[] = {
	BPF_STMT(BPF_LD|BPF_ABS|BPF_H, 4),		/* 0: ldh [4]	          */
	BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __constant_htons(RTM_NEWROUTE), 0, 3),	
							/* 1: jeq 0x18 jt 2 jf 5  */
	BPF_STMT(BPF_LD|BPF_ABS|BPF_B, 23),		/* 2: ldb [23]		  */
	BPF_JUMP(BPF_JMP+ BPF_B, RTPROT_ZEBRA, 2, 0),
							/* 3: jeq 0xb jt 4  jf 5  */

	BPF_STMT(BPF_RET|BPF_K, 0),			/* 4: ret 0               */
	BPF_STMT(BPF_RET|BPF_K, 0xffff),		/* 5: ret 0xffff          */
};


int main(int ac, char **av)
{
	int i, sk, cc;
	struct sockaddr_nl snl = {
		.nl_family = AF_NETLINK,
	};
	socklen_t snl_len = sizeof snl;
	pid_t pid;
	unsigned char buf[4096];
	struct sock_fprog prog = {
		.len = sizeof(filter) / sizeof(filter[0]),
		.filter = filter,
	};
	
	for (i = 0; i < prog.len; i++ )
		printf("%d: %#04x %d %d %#08x\n", i,
		       filter[i].code, filter[i].jt, filter[i].jf, filter[i].k);
	printf("\n");
	fflush(stdout);

	sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_USERSOCK);
	if (sk < 0)
		perror("socket");

	if (bind(sk, (struct sockaddr *) &snl, sizeof snl) < 0)
		perror("bind");
	
	if (getsockname(sk, (struct sockaddr *) &snl, &snl_len) < 0)
		perror("getsockname");
	
	if (setsockopt(sk, SOL_SOCKET, SO_ATTACH_FILTER, &prog, sizeof(prog)) < 0) 
		perror("setsockopt attach filte");

	pid = fork();
	if (pid == 0) {
		struct nlmsghdr *nlh;
		do {
			struct rtmsg *r;
			cc = recv(sk, &buf, sizeof buf, 0);
			if (cc < 0)
				perror("recv");
			
			for (i = 0; i < 64 && i < cc; i++)
				printf("%02x%c", buf[i],
				       (i % 16) == 15 ? '\n' : ' ');

			nlh = (struct nlmsghdr *) buf;
			printf("\n\tlen=%d type=%s flags=%#x seq=%#x pid=%d\n",
			       nlh->nlmsg_len, nltypes[nlh->nlmsg_type],
			       nlh->nlmsg_flags, nlh->nlmsg_seq, nlh->nlmsg_pid);

			r = NLMSG_DATA(nlh);
			printf("\tfamily=%d table=%d proto=%d type=%#x flags=%#x\n\n",
			       r->rtm_family, r->rtm_table, r->rtm_protocol,
			       r->rtm_type, r->rtm_flags);

		} while (nlh->nlmsg_type != RTM_DELLINK);
		exit(0);
	} else {
		cc = fill_info(buf, 0, 1, RTM_NEWLINK, 0, RTPROT_UNSPEC);
		if (sendto(sk, buf, cc, 0,
			   (struct sockaddr *) &snl, snl_len) < 0)
			perror("sendto");

		cc = fill_info(buf, 0, 1, RTM_NEWROUTE, RTM_F_CLONED, RTPROT_UNSPEC);
		if (sendto(sk, buf, cc, 0,
			   (struct sockaddr *) &snl, snl_len) < 0)
			perror("sendto");

		cc = fill_info(buf, 0, 1, RTM_NEWROUTE, 0, RTPROT_ZEBRA);
		if (sendto(sk, buf, cc, 0,
			   (struct sockaddr *) &snl, snl_len) < 0)
			perror("sendto");

		cc = fill_info(buf, 0, 1, RTM_NEWROUTE, 0, RTPROT_UNSPEC);
		if (sendto(sk, buf, cc, 0,
			   (struct sockaddr *) &snl, snl_len) < 0)
			perror("sendto");

		cc = fill_info(buf, 0, 1, RTM_DELLINK, 0, RTPROT_UNSPEC);
		if (sendto(sk, buf, cc, 0,
			   (struct sockaddr *) &snl, snl_len) < 0)
			perror("sendto");

		waitpid(pid, NULL, 0);
	}

	return 0;
}