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