Unable to Unmarshall to types.Struct with Protobuf

I am working on a legacy Go app that it's driving me crazy in terms of type definition.

At some point I need to return a value with the value types.Struct (from github.com/gogo/protobuf/types).

Here is the signature for the function:

GetDeviceConfig(ctx context.Context, in *DeviceID, opts ...grpc.CallOption) (*types.Struct, error)

I'm getting the value from a Postgres database (with GORM) using a string column called "config". It could be any type of JSON.

Just an example:

{"fields":{"A":{"Kind":{"string_value":"B"}},"C":{"Kind":{"string_value":"D"}}}}

When I try to unmarshall to a map[string]interface{} it works like a charm:

err := client.DB.Where("id = ?", id, 0).First(&device).Error
	if err != nil && err != gorm.ErrRecordNotFound {
		return nil, err
	}
	var dat map[string]interface{}
	if err := json.Unmarshal([]byte(device.Config), &dat); err != nil {
		panic(err)
	}

but I need to conver it to types.Struct (valid protobuf signature that cannot be changed). My best guess was something like this:

// convert json to struct
	s := types.Struct{}
	if err := json.Unmarshal([]byte(device.Config), &s); err != nil {
		panic(err)
	}
	// fmt.Println(s)

but s is empty. No data is populated.

Any help?

In order to unmarshal JSON into a Struct, you need to use Unmarshaler found in the jsonpb package. Something along the following lines should work:

err := jsonpb.UnmarshalString(device.Config, &s)
[...]

You can find further examples in jsonpb_test.go.