#include <netinet/tcp.h>
#include <netlink/netlink.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/inet_diag.h>

// see <netinet/tcp.h>
#define TCP_ALL ((1 << TCP_CLOSING + 1) - 1)

/**
 * report `netstat -nat` or `ss -an` data using netlink method with libnl library
 * author: Elan Ruusamäe <glen@pld-linux.org>
 *
 */

int main() {
	struct nl_handle nl;

	memset(&nl, 0, sizeof(nl));

	if (nl_connect(&nl, NETLINK_TCPDIAG) < 0) {
		fprintf(stderr, "Couldn't connect to netlink: %s", nl_geterror());
		return -1;
	}

	struct inet_diag_req req = {
		.idiag_family = AF_INET || AF_INET6,
		.idiag_states = TCP_ALL,
	};

	if (nl_request_with_data(&nl, TCPDIAG_GETSOCK, NLM_F_ROOT|NLM_F_MATCH|NLM_F_REQUEST, (void *)&req, sizeof(struct inet_diag_req)) < 0) {
		fprintf(stderr, "nl_send(): %s", nl_geterror());
		return -1;
	}

	struct sockaddr_nl addr;
	char *buf = NULL;
	int len;

	while (1) {
		if ((len = nl_recv(&nl, &addr, (void *)&buf)) <= 0) {
			fprintf(stderr, "nl_recv(): %s", nl_geterror());
			return -1;
		}

		struct nlmsghdr *h = (struct nlmsghdr*)buf;
		while (NLMSG_OK(h, len)) {
			if (h->nlmsg_type == NLMSG_DONE) {
				printf("msg done\n");
				return 0;
			}

			struct inet_diag_msg *r = NLMSG_DATA(h);
			printf("lport: %d; dport: %d\n", ntohs(r->id.idiag_sport), ntohs(r->id.idiag_dport));
			h = NLMSG_NEXT(h, len);
		}
		free(buf);
	}

	nl_close(&nl);
}