code: func isTCP4AddrResolvable(fl FieldLevel) bool {
  
  	if !isIP4Addr(fl) {
  		return false
  	}
  
  	_, err := net.ResolveTCPAddr("tcp4", fl.Field().String())
  	return err == nil
  }
docs: // IsTCP4AddrResolvable is the validation function for validating if the field's value is a resolvable tcp4 address.