bloblang.Executor.Query with a custom struct (not a map[string]interface{})

[oliverpool]

Hi,
I am exploring if bloblang could be used inside gitea for webhook payload transformation (go-gitea/gitea#19307 (comment))

I have a working prototype, however it is quite hacky since it seems that bloblang.Executor.Query only works properly with an argument of type map[string]interface{} and not with arbitrary struct.

Code example:

func TestBloblang(t *testing.T) {
	env := bloblang.NewEnvironment().WithoutFunctions("env", "file")

	mapping := `
root.type = this.type()
root.this = this
root.sha = this.sha
root.Sha = this.Sha
`
	exe, err := env.Parse(mapping)
	if err != nil {
		panic(err)
	}
	res, err := exe.Query(struct {
		Sha     string `json:"sha"`
		Ref     string `json:"ref"`
		RefType string `json:"ref_type"`
	}{
		Sha:     "sha1",
		Ref:     "some/ref",
		RefType: "tags",
	})
	if err != nil {
		panic(err)
	}
	b, err := json.Marshal(res)
	if err != nil {
		panic(err)
	}
	t.Log(string(b))
	t.Fail() // so that t.Log is shown
}

Output:

--- FAIL: TestBloblang (0.00s)
    bloblang_test.go:48: {"Sha":null,"sha":null,"this":{"sha":"sha1","ref":"some/ref","ref_type":"tags"},"type":"unknown"}

Currently to get an object inside bloblang, I json-marshal my struct and unmarshal it in a map[string]interface{} object...
Is there any cleaner way to get a proper object inside bloblang without marshalling+unmarshalling?

[Jeffail]

Hey @oliverpool, the bloblang engine doesn't support reflection of struct types when expanding fields so any data that you want mappings to be able to traverse needs to be in maps and empty interface slices.

Adding reflection is something I'd possibly be open to but for now it might be cleaner to use https://github.com/mitchellh/mapstructure as that'd save you the performance hit of byte serialization back and forth.

[oliverpool]

Thank your for the quick reply!
I don't think that https://github.com/mitchellh/mapstructure works in my case, since I already have a struct, which I need to transform to a map[string]interface to use bloblang (and not the other way around).

I can use mapstructure on the result if I want to reconstruct a nice structure.

I proposed a fix in the gabs package: Jeffail/gabs#122 let me know what you think