ResolveIP with a host, return ip.

LookupIPv4 with a host, return ipv4 list.

LookupIPv6 with a host, return ipv6 list.

LookupIPWithResolver same as ResolveIP, but with a resolver.

ResolveIP with a host, return ip.

ResolveIPv4 with a host, return ipv4.

ResolveIPv6 with a host, return ipv6.

DefaultDNSTimeout defined the default dns request timeout.

DefaultHosts aim to resolve hosts.

DefaultResolver aim to resolve ip.

DisableIPv6 means don't resolve ipv6 host default value is true.