package errhttp type PaymentRequired interface { ClientError PaymentRequired() } type internalPaymentRequired struct { err error } func PaymentRequiredWrap(err error) error { return internalPaymentRequired{ err:err, } } func (receiver internalPaymentRequired) Error() string { return receiver.err.Error() } func (receiver internalPaymentRequired) Err() error { return receiver.err } func (internalPaymentRequired) ClientError() { // Nothing here. } func (internalPaymentRequired) PaymentRequired() { // Nothing here. }