code: func btcdLookup(host string) ([]net.IP, error) {
  	if strings.HasSuffix(host, ".onion") {
  		return nil, fmt.Errorf("attempt to resolve tor address %s", host)
  	}
  
  	return cfg.lookup(host)
  }
docs: // btcdLookup resolves the IP of the given host using the correct DNS lookup
  // function depending on the configuration options.  For example, addresses will
  // be resolved using tor when the --proxy flag was specified unless --noonion
  // was also specified in which case the normal system DNS resolver will be used.
  //
  // Any attempt to resolve a tor address (.onion) will return an error since they
  // are not intended to be resolved outside of the tor proxy.