Package dnsutil contains higher-level methods useful with the dns package. While package dns implements the DNS protocols itself, these functions are related but not directly required for protocol processing. They are often useful in preparing input/output of the functions in package dns.
AddOrigin adds origin to s if s is not already a FQDN. Note that the result may not be a FQDN. If origin does not end with a ".", the result won't either. This implements the zonefile convention (specified in RFC 1035, Section "5.1. Format") that "@" represents the apex (bare) domain. i.e. AddOrigin("@", "foo.com.") returns "foo.com.".
TrimDomainName trims origin from s if s is a subdomain. This function will never return "", but returns "@" instead (@ represents the apex domain).