Function UnwrapOnce

errbase/unwrap.go:40–48

Sadly the go 2/1.13 design for errors has promoted the name `Unwrap()` for the method that accesses the cause, whilst the ecosystem has already chosen `Cause()`. In order to unwrap reliably, we must thus support both. See: https://github.com/golang/go/issues/31778 UnwrapOnce accesses the direct cau

(err error)

// The go stdlib does not define output on `Unwrap()` for a multi-cause
// error, so we default to nil here.
func UnwrapOnce(err error) (cause error) {
	switch e := err.(type) {
	case interface{ Cause() error }:
		return e.Cause()
	case interface{ Unwrap() error }:
		return e.Unwrap()
	}
	return nil
}

// UnwrapAll accesses the root cause object of the error.
// If the error has no cause (leaf error), it is returned directly.