7 #include <sys/socket.h>
10 #include <arpa/inet.h>
12 static char *get_sockname(struct addrinfo *addr) {
13 static char buf[INET6_ADDRSTRLEN+1];
14 struct sockaddr_storage local;
18 if ((fd = socket(addr->ai_family, SOCK_DGRAM, 0)) == -1) {
23 /* Since the socket was created with SOCK_DGRAM, this is
24 * actually not establishing a connection or generating
25 * any other network traffic. Instead, as a side-effect,
26 * it saves the local address with which packets would
27 * be sent to the destination. */
28 if (connect(fd, addr->ai_addr, addr->ai_addrlen) == -1) {
29 /* We don’t display the error here because most
30 * likely, there just is no IPv6 connectivity.
31 * Thus, don’t spam the user’s console but just
32 * try the next address. */
37 socklen_t local_len = sizeof(struct sockaddr_storage);
38 if (getsockname(fd, (struct sockaddr*)&local, &local_len) == -1) {
39 perror("getsockname()");
44 memset(buf, 0, INET6_ADDRSTRLEN + 1);
45 if ((ret = getnameinfo((struct sockaddr*)&local, local_len,
46 buf, sizeof(buf), NULL, 0,
47 NI_NUMERICHOST)) != 0) {
48 fprintf(stderr, "getnameinfo(): %s\n", gai_strerror(ret));
58 * Returns the IPv6 address with which you have connectivity at the moment.
59 * The char * is statically allocated and mustn't be freed
61 static char *get_ipv6_addr() {
62 struct addrinfo hints;
63 struct addrinfo *result, *resp;
64 static struct addrinfo *cached = NULL;
66 /* To save dns lookups (if they are not cached locally) and creating
67 * sockets, we save the fd and keep it open. */
69 return get_sockname(cached);
71 memset(&hints, 0, sizeof(struct addrinfo));
72 hints.ai_family = AF_INET6;
73 hints.ai_socktype = SOCK_DGRAM;
75 /* We resolve the K root server to get a public IPv6 address. You can
76 * replace this with any other host which has an AAAA record, but the
77 * K root server is a pretty safe bet. */
78 if (getaddrinfo("k.root-servers.net", "domain", &hints, &result) != 0) {
79 /* We don’t display the error here because most
80 * likely, there just is no connectivity.
81 * Thus, don’t spam the user’s console. */
85 for (resp = result; resp != NULL; resp = resp->ai_next) {
86 char *addr_string = get_sockname(resp);
87 /* If we could not get our own address and there is more than
88 * one result for resolving k.root-servers.net, we cannot
89 * cache. Otherwise, no matter if we got IPv6 connectivity or
90 * not, we will cache the (single) result and are done. */
91 if (!addr_string && result->ai_next != NULL)
94 if ((cached = malloc(sizeof(struct addrinfo))) == NULL)
96 memcpy(cached, resp, sizeof(struct addrinfo));
97 if ((cached->ai_addr = malloc(resp->ai_addrlen)) == NULL) {
101 memcpy(cached->ai_addr, resp->ai_addr, resp->ai_addrlen);
102 freeaddrinfo(result);
106 freeaddrinfo(result);
110 void print_ipv6_info(const char *format_up, const char *format_down) {
112 char *addr_string = get_ipv6_addr();
114 if (addr_string == NULL) {
115 printf("%s", format_down);
119 for (walk = format_up; *walk != '\0'; walk++) {
125 if (strncmp(walk+1, "ip", strlen("ip")) == 0) {
126 printf("%s", addr_string);
127 walk += strlen("ip");