golang pkg/errors How to print custom wrapped errors?

Question

My project wraps a custom error type errNotFound, which has an error embedded in it. Now I have a pkg/errors package that generates an error that prints the call stack. But when I inline this error into errNotFound, the call stack is not printed. Here is a sample, how can I change it?

simple:

package main import ( "fmt" stderrors "errors" "github.com/pkg/errors" ) func findSomething() error { return errors.Errorf("something not found") } func main() { err := findSomething() // can print error stack exitf("Error1: %+v", err) fmt.Println() fmt.Println() // cannot print error stack err = ErrNotFound(err) exitf("Error2: %+v", err) } func exitf(format string, args ...interface{}) { fmt.Printf(format, args...) //os.Exit(1) } type errNotFound struct{ error } func ErrNotFound(err error) error { if err == nil || IsErrNotFound(err) { return err } return errNotFound{err} } func IsErrNotFound(err error) bool { return stderrors.As(err, &errNotFound{}) }

output:

$ go run main Error1: something not found main.findSomething /home/lianxm/github.com/play_error/main.go:11 main.main /home/lianxm/github.com/play_error/main.go:15 runtime.main /usr/local/go/src/runtime/proc.go:255 runtime.goexit /usr/local/go/src/runtime/asm_amd64.s:1581 Error2: something not found

I know I can get the original error by err = errors.Unwrap(err) and then print it, but this means that I need to do this every time before printing, which is not very elegant code, and I don't really want to do that...

here is an example project: https://github.com/lianxmfor/play_error

maybe errorNotFound implement fmt.Formatter can solve this, but i cannot how to implement the interface 😿 — xm lian
– xm lian, Commented Jan 25, 2022 at 15:42

Kelvin Floresta de Andrade · Accepted Answer · 2022-01-25 16:09:29Z

1

Is this necessary to put an error inside another if you already have your stack?

If yes... You can define a Method for errNotFound like:

func (e errNotFound) Error() string { return fmt.Printf("NotFound: %+v", e.err) }

answered Jan 25, 2022 at 16:09

Kelvin Floresta de Andrade

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2 Comments

xm lian Over a year ago

Yes, I need to put the error in errNotFound, which is very useful for me, see here: go.dev/play/p/VNJBWfbhhQZ

xm lian Over a year ago

This method solves my problem, thank you!

serge-v · Accepted Answer · 2022-01-25 19:16:22Z

you need to annotate the error with stack:

func ErrNotFound(err error) error { if err == nil || IsErrNotFound(err) { return err } return errors.WithStack(errNotFound{err}) }

Yes, I can do that, thank you! But that would print out multiple call stacks, which I don't really want to do.

Manish Kushwaha · Accepted Answer · 2022-01-25 19:33:32Z

0

while calling exitf you can use errors.WithStack to print stack trace.

answered Jan 25, 2022 at 19:33

Manish Kushwaha

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1 Comment

xm lian Over a year ago

This has the same effect as calling errors.Unwrap before each exitf call, which I don't really want to do, it's not very elegant

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