code: func (ds *DNSServer) GetA(fqdn string) *dns.A {
  	ds.aMutex.RLock()
  	defer ds.aMutex.RUnlock()
  	val, ok := ds.aRecords[fqdn]
  
  	if ok {
  		return &dns.A{
  			Hdr: dns.RR_Header{
  				Name:   fqdn,
  				Rrtype: dns.TypeA,
  				Class:  dns.ClassINET,
  				// 0 TTL results in UB for DNS resolvers and generally causes problems.
  				Ttl: 1,
  			},
  			A: val,
  		}
  	}
  
  	return nil
  }
docs: // Receives a FQDN; looks up and supplies the A record.