-static char *get_ipv6_addr() {
- struct addrinfo hints;
- struct addrinfo *result, *resp;
- static struct addrinfo *cached = NULL;
-
- /* To save dns lookups (if they are not cached locally) and creating
- * sockets, we save the fd and keep it open. */
- if (cached != NULL)
- return get_sockname(cached);
-
- memset(&hints, 0, sizeof(struct addrinfo));
- hints.ai_family = AF_INET6;
-
- /* We resolve the K root server to get a public IPv6 address. You can
- * replace this with any other host which has an AAAA record, but the
- * K root server is a pretty safe bet. */
- if (getaddrinfo("k.root-servers.net", "domain", &hints, &result) != 0) {
- /* We don’t display the error here because most
- * likely, there just is no connectivity.
- * Thus, don’t spam the user’s console. */
- return NULL;
- }
-
- for (resp = result; resp != NULL; resp = resp->ai_next) {
- char *addr_string = get_sockname(resp);
- if (!addr_string)
- continue;
-
- if ((cached = malloc(sizeof(struct addrinfo))) == NULL)
- return NULL;
- memcpy(cached, resp, sizeof(struct addrinfo));
- if ((cached->ai_addr = malloc(resp->ai_addrlen)) == NULL) {
- cached = NULL;
- return NULL;
- }
- memcpy(cached->ai_addr, resp->ai_addr, resp->ai_addrlen);
- freeaddrinfo(result);
- return addr_string;
+static char *get_ipv6_addr(void) {
+ struct addrinfo hints;
+ struct addrinfo *result, *resp;
+ static struct addrinfo *cached = NULL;
+
+ /* To save dns lookups (if they are not cached locally) and creating
+ * sockets, we save the fd and keep it open. */
+ if (cached != NULL)
+ return get_sockname(cached);
+
+ memset(&hints, 0, sizeof(struct addrinfo));
+ hints.ai_family = AF_INET6;
+ hints.ai_socktype = SOCK_DGRAM;
+
+ /* We use the public IPv6 of the K root server here. It doesn’t matter
+ * which IPv6 address we use (we don’t even send any packets), as long
+ * as it’s considered global by the kernel.
+ * NB: We don’t use a hostname since that would trigger a DNS lookup.
+ * By using an IPv6 address, getaddrinfo() will *not* do a DNS lookup,
+ * but return the address in the appropriate struct. */
+ if (getaddrinfo("2001:7fd::1", "domain", &hints, &result) != 0) {
+ /* We don’t display the error here because most
+ * likely, there just is no connectivity.
+ * Thus, don’t spam the user’s console. */
+ return NULL;
+ }
+
+ for (resp = result; resp != NULL; resp = resp->ai_next) {
+ char *addr_string = get_sockname(resp);
+ /* If we could not get our own address and there is more than
+ * one result for resolving k.root-servers.net, we cannot
+ * cache. Otherwise, no matter if we got IPv6 connectivity or
+ * not, we will cache the (single) result and are done. */
+ if (!addr_string && result->ai_next != NULL)
+ continue;
+
+ if ((cached = malloc(sizeof(struct addrinfo))) == NULL)
+ return NULL;
+ memcpy(cached, resp, sizeof(struct addrinfo));
+ if ((cached->ai_addr = malloc(resp->ai_addrlen)) == NULL) {
+ cached = NULL;
+ return NULL;