+
+#ifdef IPV6_V6ONLY
+ /* This OS supports IPv6 sockets that can also listen for IPv4
+ * connections. If our address is "*" or empty, enable both v4 and v6 to
+ * allow for simpler configuration on dual-stack hosts. Otherwise, if it
+ * is "::" or an IPv6 address, disable support so that an IPv4 bind will
+ * work on the port (by us or another application).
+ */
+ if (bind_to.sa.sa_family == AF_INET6)
+ {
+ std::string addr = tag->getString("address");
+ /* This must be >= sizeof(DWORD) on Windows */
+ const int enable = (addr.empty() || addr == "*") ? 0 : 1;
+ /* This must be before bind() */
+ setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, reinterpret_cast<const char *>(&enable), sizeof(enable));
+ // errors ignored intentionally