Representing multiple errors in Go

Question

The MediaWiki API may return multiple errors. Is this a idiomatic way of representing them?

type MediaWikiError struct {
    Code    string      `json:"code"`
    Data    interface{} `json:"data"`
    Message string      `json:"text"`
    Module  string      `json:"module"`
}

func (e *MediaWikiError) Error() string {
    return fmt.Sprintf("MediaWiki module \"%s\" reported an error: %s (%s)", e.Module, e.Message, e.Code)
}

type MediaWikiErrors []*MediaWikiError

func (e MediaWikiErrors) Error() string {
    switch len(e) {
    case 0:
        return ""
    case 1:
        return e[0].Error()
    default:
        codes := make([]string, len(e))
        for i, err := range e {
            codes[i] = err.Code
        }
        return fmt.Sprintf("MediaWiki API reported multiple errors: %s", strings.Join(codes, ", "))
    }
}

felix · Accepted Answer · 2018-05-23 05:37:09Z

1

+100

1. Don't use \" in string

Go provide a very nice way to handle quote (") in strings:

instead of

fmt.Sprintf("MediaWiki module \"%s\" reported an error: %s (%s)", ...)

you can use

fmt.Sprintf(`MediaWiki module "%s" reported an error: %s (%s)`, ...)

It's easier and nicer to read

2. Use range loop instead of switch

Instead of specifiying behavior for 3 cases ( 0, 1, default), we can use a simple range loop

So this

func (e MediaWikiErrors) Error() string {
    switch len(e) {
    case 0:
        return ""
    case 1:
        return e[0].Error()
    default:
        codes := make([]string, len(e))
        for i, err := range e {
            codes[i] = err.Code
        }
        return fmt.Sprintf("MediaWiki API reported multiple errors: %s", strings.Join(codes, ", "))
    }
}

become simply this:

func (e MediaWikiErrors) Error() (errMsg string) {
    for _, err := range e {
        errMsg += err.Error() + "\n"
    }
    return errMsg
}

I prefer joining errors with a line return (\n) instead of a comma, but it's just my personal taste. Multiple errors would be printed like this:

MediaWiki module "module_1" reported an error: parsing error (3)
MediaWiki module "module_2" reported an error: access denied (22)

answered May 23 '18 at 5:37

felix

5784 silver badges14 bronze badges

\$\begingroup\$ That are some useful suggestion, but it doesn't answer my question. Is it idiomatic to represent multiple errors in this way? \$\endgroup\$ – user103180 May 23 '18 at 5:43
\$\begingroup\$ @R3turnz I guess it is. The MongoDB driver use something similar to handle bulk insert error for example. The best way to now is to look at how the standard library / project maintained by go authors handle similar problems \$\endgroup\$ – felix May 23 '18 at 6:07
\$\begingroup\$ Do you have an example where the Go authors faced a similar problem? \$\endgroup\$ – user103180 May 23 '18 at 6:37
\$\begingroup\$ @R3turnz maybe golint source. It reads .go file, and then print all "style" error \$\endgroup\$ – felix May 23 '18 at 7:10
\$\begingroup\$ In addition to your comment wrt using back-tick string literals you can also get rid of the quotes in the format string by replacing "%s" with %q which is more readable and handles issues such as as the string argument itself contains a character that needs quoting. \$\endgroup\$ – Dave C Sep 3 '18 at 19:33

Add a comment |

Roland Illig · Accepted Answer · 2018-05-23 06:02:16Z

0

Yes, it is idiomatic. You have access to all relevant details of the individual errors, as well as you have implemented the error interface.

I don't think there should ever be an empty MediawikiErrors object, or at least its Error function should never be called, but for convenience returning an empty string there is fine.

answered May 23 '18 at 6:02

Roland Illig

20.5k2 gold badges30 silver badges77 bronze badges

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1. Don't use \" in string

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