#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <arpa/inet.h>

/*
 * Returns the IPv6 address with which you have connectivity at the moment.
 *
 */
const char *get_ipv6_addr() {
	static char buf[INET6_ADDRSTRLEN+1];
	struct addrinfo hints;
	struct addrinfo *result, *resp;
	int fd;

	memset(&hints, 0, sizeof(struct addrinfo));
	hints.ai_family = AF_INET6;

	if (getaddrinfo("k.root-servers.net", "domain", &hints, &result) != 0) {
		perror("getaddrinfo()");
		return "no IP";
	}

	for (resp = result; resp != NULL; resp = resp->ai_next) {
		if ((fd = socket(resp->ai_family, SOCK_STREAM, 0)) == -1) {
			perror("socket()");
			continue;
		}

		if (connect(fd, resp->ai_addr, resp->ai_addrlen) == -1) {
			perror("connect()");
			continue;
		}

		struct sockaddr_storage local;
		socklen_t local_len = sizeof(struct sockaddr_storage);
		if (getsockname(fd, (struct sockaddr*)&local, &local_len) == -1) {
			perror("getsockname()");
			return "no IP";
		}

		memset(buf, 0, INET6_ADDRSTRLEN + 1);
		int ret;
		if ((ret = getnameinfo((struct sockaddr*)&local, local_len, buf, sizeof(buf), NULL, 0, NI_NUMERICHOST)) != 0) {
			fprintf(stderr, "getnameinfo(): %s\n", gai_strerror(ret));
			return "no IP";
		}

		(void)close(fd);

		free(result);
		return buf;
	}

	free(result);
	return "no IP";
}