How to return a custom user friendly error message in Kubernetes?

Question

I have a backend with golang that talks to k8s. I want to reformulate the error response that i get from k8s and send it to the frontend.

I want to return a meaningful validation error messages for the user, when he add a non valid name, something already exist ...

And i want something generic not hardcoded in each endpoint's controller.

I am using kubernetes/client-go.

1. First error:

For example lets say i want to add a hotel to the etcd, when i try to add the hotel's name: hotel123, that's already exist.

• I get this error message: \"hotel123\" already exists.
• What i want : hotel123 already exists.

2. second error:

For example lets say i want to add a hotel to the etcd, when i try to add the hotel name: hotel_123, that's alerady exist.

• I get this error message: \"hotel_123\" is invalid, Invalid value: \"hotel_123\"...
• What i want: hotel_123 is invalid

How to return a custom user friendly error message ?

PS: i have multiple functions, so the validation should be generic.

Answer 1

In general (although there are workarounds), if you want to trap an error in order to return a more useful error, you want to ensure the following conditions are met:

1. The error you're trapping has a meaningful type
2. You're using go version >= 1.13 which ships with useful helper functions

In the following example I'm trying to read a config file that doesn't exist. My code checks that the error returned is a fs.PathError and then throws it's own more useful error. You can extend this general idea to your use case.

package main

import (
    "errors"
    "fmt"
    "io/fs"

    "k8s.io/client-go/tools/clientcmd"
)

func main() {

    var myError error
    config, originalError := clientcmd.BuildConfigFromFlags("", "/some/path/that/doesnt/exist")
    if originalError != nil {

        var pathError *fs.PathError

        switch {
        case errors.As(originalError, &pathError):

            myError = fmt.Errorf("there is no config file at %s", originalError.(*fs.PathError).Path)

        default:

            myError = fmt.Errorf("there was an error and it's type was %T", originalError)

        }

        fmt.Printf("%#v", myError)

    } else {

        fmt.Println("There was no error")
        fmt.Println(config)

    }

}

In your debugging, you will find the %T formatter useful.

For your specific use-case, you can use a Regex to parse out the desired text.

The regex below says:

1. ^\W* start with any non-alhpanumeric characters
2. (\w+) capture the alphanumeric string following
3. \W*\s? match non-alphanumeric characters
4. (is\sinvalid) capture "is invalid"

func MyError(inError error) error {
    pattern, _ := regexp.Compile(`^\W*(\w+)\W*\s?(is\sinvalid)(.*)$`)
    myErrorString := pattern.ReplaceAll([]byte(inError.Error()), []byte("$1 $2"))
    return errors.New(string(myErrorString))
}

As seen on this playground:

https://goplay.tools/snippet/bcZO7wa8Vnl