// TrimDomainName trims origin from s if s is a subdomain.
// This function will never return "", but returns "@" instead (@ represents the apex (bare) domain).
func TrimDomainName(s, origin string) string {
// An apex (bare) domain is always returned as "@".
// If the return value ends in a ".", the domain was not the suffix.
// origin can end in "." or not. Either way the results should be the same.
if len(s) == 0 {
return "@" // Return the apex (@) rather than "".
}
// Someone is using TrimDomainName(s, ".") to remove a dot if it exists.
if origin == "." {
return strings.TrimSuffix(s, origin)
}
// Dude, you aren't even if the right subdomain!
if !dns.IsSubDomain(origin, s) {
return s
}
slabels := dns.Split(s)
olabels := dns.Split(origin)
m := dns.CompareDomainName(s, origin)
if len(olabels) == m {
if len(olabels) == len(slabels) {
return "@" // origin == s
}
if (s[0] == '.') && (len(slabels) == (len(olabels) + 1)) {
return "@" // TrimDomainName(".foo.", "foo.")
}
}
// Return the first (len-m) labels:
return s[:slabels[len(slabels)-m]-1]
}
// saveDNSRR saves 1 or more DNS records to the resolver cache.
func (r *Resolver) saveDNSRR(host string, qname string, drrs []dns.RR) RRs {
var rrs RRs
cl := dns.CountLabel(qname)
for _, drr := range drrs {
rr, ok := convertRR(drr)
if !ok {
continue
}
if dns.CountLabel(rr.Name) < cl && dns.CompareDomainName(qname, rr.Name) < 2 {
// fmt.Fprintf(os.Stderr, "Warning: potential poisoning from %s: %s -> %s\n", host, qname, drr.String())
continue
}
r.cache.add(rr.Name, rr)
rrs = append(rrs, rr)
}
return rrs
}