+
+#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.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
+ }
+#endif
+
+ if (tag->getBool("free"))
+ {
+ socklen_t enable = 1;
+#if defined IP_FREEBIND // Linux 2.4+
+ setsockopt(fd, SOL_IP, IP_FREEBIND, &enable, sizeof(enable));
+#elif defined IP_BINDANY // FreeBSD
+ setsockopt(fd, IPPROTO_IP, IP_BINDANY, &enable, sizeof(enable));
+#elif defined SO_BINDANY // NetBSD/OpenBSD
+ setsockopt(fd, SOL_SOCKET, SO_BINDANY, &enable, sizeof(enable));
+#else
+ (void)enable;
+#endif