Dedup de-duplicates a message.

DuplicateCNAME returns true if r already exists in records.

ExtractAddressFromReverse turns a standard PTR reverse record name into an IP address.

Join joins labels to form a fully qualified domain name.

ParseHostPort will check if the host part is a valid IP address, if the IP address is valid, but no port is found, defaultPort is added.

ParseHostPortOrFile parses the strings in s, each string can either be a address, address:port or a filename.

TrimZone removes the zone component from q.