passing a complex object from js to go function does not unmarshal all fields

[scottkgaran]

Brief summary

Hi all, I am currently writing a k6 extension.

I am trying to pass a "complex" object from js to my go function. But for some reason I do not get back all the fields on the go side.

I have noticed this with structs within structs as well as type alias's.

import magic from 'k6/x/magic';

export default function () {
  const vars = {
    order: {
      id: 'wakka',
      sku: {
        id: 'magic'
      }
    },
    superStatus: 'XLARGE',
    countryPopStar: {
      id: '9001'
    },
    normal: 'string'
  };

  magic(vars);
}

type Order struct {
	Id  string `json:"id"`
	Sku SKU    `json:"sku"`
}

type SKU struct {
	Id string `json:"id"`
}

type CountryPopStar struct {
	Id string `json:"id"`
}

type SuperStatus string

type TestStruct struct {
	*Order          `json:"order,omitempty"`
	*SuperStatus    `json:"superStatus"`
	*CountryPopStar `json:"countryPopStar"`
	Normal          *string `json:"normal"`
}

func Magic(ts *TestStruct) {
	logger.Info(ts.String())
}

Happy to create a repro repo if needed.

k6 version

latest, master

OS

windows wsl (arch)

Docker version and image (if applicable)

No response

Steps to reproduce the problem

1. write an extension that has some complex structs and create a function that uses that struct as an argument
2. call that function from your script and pass in the js object
3. notice not all fields get deserialized

Do the same thing using sobek runtime directly (via test):

1. take your js script and pass it in as a string to RunString (removing the import)
2. setup sobek runtime with function and logger to see output
3. view output and all fields are accounted for

example:

func TestThatMagic(t *testing.T) {
	vm := sobek.New()
	vm.SetFieldNameMapper(sobek.TagFieldNameMapper("json", true))
	vm.Set("magic", magic)
	vm.Set("log", log)

	_, err := vm.RunString(SCRIPT)
	if err != nil {
		panic(err)
	}
}

Expected behaviour

we should be able to unmarshal objects properly like vanilla sobek can.

Actual behaviour

struct does not contain the field data:

 {
   "order": {
     "id": "",
     "sku": {
       "id": ""
     }
   },
   "superStatus": "[object Object]", // this is ok
   "countryPopStar": {
     "id": ""
   },
   "normal": "string" // this works
 }

[olegbespalov]

Hi @scottkgaran

Sorry for the long reply 😢

I guess the issue here is the and if you tried to use this in k6 as an extension.

vm.SetFieldNameMapper(sobek.TagFieldNameMapper("json", true))

We allow only js tag for mapping the tags.

So, if you can, your structs should look like:

type SKU struct {
	Id string `js:"id"`
}

Here is the working example:

package magic

import (
	"fmt"
	"testing"

	"github.com/grafana/sobek"
)

const SCRIPT = `
let vars = {id: '123', details: {name: 'John Doe', note: 'lorem ipsum', more_details: {age: 30}}};
magic(vars);
`

type Order struct {
	Id      string `js:"id"`
	Details struct {
		Name        string `js:"name"`
		Note        string `js:"note"`
		MoreDetails struct {
			Age int `js:"age"`
		} `js:"more_details"`
	} `js:"details"`
}

type module struct {
	rt *sobek.Runtime
}

func (m *module) Magic(v sobek.Value) string {
	xx := &Order{}

	if err := m.rt.ExportTo(v, xx); err != nil {
		panic(err)
	}

	return fmt.Sprintf("Id: %s, Name: %s, Note: %s", xx.Id, xx.Details.Name, xx.Details.Note)
}

func TestThatMagic(t *testing.T) {
	vm := sobek.New()
        // this is what used in k6
	vm.SetFieldNameMapper(sobek.TagFieldNameMapper("js", true))

	module := &module{rt: vm}
	vm.Set("magic", module.Magic)

	result, err := vm.RunString(SCRIPT)
	if err != nil {
		panic(err)
	}

	str := result.ToString().String()

	expected := "Id: 123, Name: John Doe, Note: lorem ipsum"
	if expected != str {
		t.Errorf("Expected %q result, got %q", expected, result)
	}
}