Help to print only one stack trace when multiple wrap

[flibustenet]

When I return an error I wrap because i'm never sure if it's already wrapped or not.
Then when i print the error with "%+v" it print all the stacks.
How can I do to only print the last stack but also all the messages ?

package main

import (
	"fmt"

	"github.com/pkg/errors"
)

func three() error {
	return errors.New("three")
}
func two() error {
	return errors.Wrap(three(), "two")
}
func one() error {
	return errors.Wrap(two(), "one")
}
func main() {
	err := one()
	fmt.Printf("%+v", err)
}

It print

three
main.three
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:10
main.two
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:13
main.one
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16
main.main
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19
runtime.main
	/usr/local/go/src/runtime/proc.go:183
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:2086
two
main.two
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:13
main.one
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16
main.main
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19
runtime.main
	/usr/local/go/src/runtime/proc.go:183
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:2086
one
main.one
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16
main.main
	/home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19
runtime.main
	/usr/local/go/src/runtime/proc.go:183
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:2086

I would like to print only the stack of three.

Thanks (and sorry for my english)

[davecheney]

Can you please explain why you want to do this?

…

On Sun, 8 Jan 2017, 23:23 Wilk ***@***.***> wrote: When I return an error I wrap because i'm never sure if it's already wrapped or not. Then when i print the error with "%+v" it print all the stacks. How can I do to only print the last stack but also all the messages ? package main import ( "fmt" "github.com/pkg/errors" ) func three() error { return errors.New("three") }func two() error { return errors.Wrap(three(), "two") }func one() error { return errors.Wrap(two(), "one") }func main() { err := one() fmt.Printf("%+v", err) } It print three main.three /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:10 main.two /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:13 main.one /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16 main.main /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19 runtime.main /usr/local/go/src/runtime/proc.go:183 runtime.goexit /usr/local/go/src/runtime/asm_amd64.s:2086 two main.two /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:13 main.one /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16 main.main /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19 runtime.main /usr/local/go/src/runtime/proc.go:183 runtime.goexit /usr/local/go/src/runtime/asm_amd64.s:2086 one main.one /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:16 main.main /home/wilk/projets/logics/medicoop/src/medicoop/t/t.go:19 runtime.main /usr/local/go/src/runtime/proc.go:183 runtime.goexit /usr/local/go/src/runtime/asm_amd64.s:2086 I would like to print only the stack of three. Thanks (and sorry for my english) — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#98>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAcAzhVsQjLnQmzmV88aGaG3EZRj90Nks5rQNUxgaJpZM4LdrSU> .

[flibustenet]

For example one is my handler, two is my lib three is where i open a file.
I have an io error on three, i wrap the error "file not found" and return it.
Then in my lib i wrap this error, add a message "i could not get my data" and return it to the handler
On my handler i wrap this error and return it to the recovery middleware where i want to print the stack of the error.
I could not wrap the error in two and one and just add a message with WithMessage, but i don't know if the original error (in three) was wrapped (if i forget) so i wrap it isn't it ?

[davecheney]

I cannot offer you a solution, only two pieces of advice. 1. I found that if my code is well factored then there was little use for WithMessage as the name of the function was near identical to the message I would have added. I suggest you look at the structure of you code and see if the stack trace naturally avoids the need to add a message at every step. Eg func ReadFile(f string) error { if err := ... ; err != nil { return errors.WithMessage(err, "ReadFile failed) // usually redundant } ... } 2. There is an open issue to added a stack trace if one does not exist, but nobody has proposed an algorithm to do this, and I'm pretty sure if we did implement this, there would be a request to skip this behaviour. My recommendation is If the error comes from outside you code, wrap it If the error is being propogated from within your code, use WithMessage if it adds real information, Otherwise, return the error untouched.

…

On Mon, 9 Jan 2017, 07:25 Wilk ***@***.***> wrote: For example one is my handler, two is my lib three is where i open a file. I have an io error on three, i wrap the error "file not found" and return it. Then in my lib i wrap this error, add a message "i could not get my data" and return it to the handler On my handler i wrap this error and return it to the recovery middleware where i want to print the stack of the error. I could not wrap the error in two and one and just add a message with WithMessage, but i don't know if the original error (in three) was wrapped (if i forget) so i wrap it isn't it ? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#98 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAcA9y0XdIwjbHA7GbZmSrDZkss3gkBks5rQUYogaJpZM4LdrSU> .

[flibustenet]

Thanks for your advice, i see now that it's a duplicate of the #75