json: cannot unmarshal array into Go struct field Attribute.attributes.values of type structpb.Value

[blakecschmidt]

What version of protobuf and what language are you using?
Protobuf version 1.3.2
Go version 1.13.5

What did you do?
I am working with the Google My Business API and I am attempting to retrieve the JSON response of a location.
https://developers.google.com/my-business/reference/rest/v4/accounts.locations/get

After retrieving the JSON, I am unmarshaling it as a Location object. This Location object contains an attribute field which is an array of Attribute objects. Within the attribute object is another array of protobuf Values.

In my Go code, I have a .go file containing all of the structs which make up this Location struct. In this file I am importing the following:

import (
	structpb "github.com/golang/protobuf/ptypes/struct"
)

And when I define this Attribute struct I define the Values with the following:

type Attribute struct {
	AttributeId string `json:"attributeId"`
	ValueType AttributeValueType `json:"valueType"`
	Values []structpb.Value `json:"values"`
	RepeatedEnumValue RepeatedEnumAttributeValue `json:"repeatedEnumValue"`
	UrlValues []UrlAttributeValue `json:"urlValues"`
}

The JSON that I am receiving from the GMB API contains the following attributes component:

"attributes": [
    {
      "attributeId": "pay_debit_card",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "has_wheelchair_accessible_elevator",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "has_service_installation",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "pay_check",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "has_delivery_same_day",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "has_gift_wrapping",
      "valueType": "BOOL",
      "values": [
        false
      ]
    },
    {
      "attributeId": "requires_cash_only",
      "valueType": "BOOL",
      "values": [
        false
      ]
    },
    {
      "attributeId": "has_wheelchair_accessible_entrance",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "has_service_repair",
      "valueType": "BOOL",
      "values": [
        true
      ]
    },
    {
      "attributeId": "wi_fi",
      "valueType": "ENUM",
      "values": [
        "free_wi_fi"
      ]
    },
    {
      "attributeId": "pay_credit_card_types_accepted",
      "valueType": "REPEATED_ENUM",
      "repeatedEnumValue": {
        "setValues": [
          "american_express",
          "discover",
          "mastercard",
          "visa"
        ]
      }

The function in which I am receiving this JSON and unmarshaling is:

func GetStore(accessToken string) {
	response, err := http.Get(fmt.Sprintf("%vaccounts/%v/locations/%v?access_token=%v", gmbBaseUri, "104256381367782693902", "10772730936382702757", accessToken))

	if err != nil {
		fmt.Printf("The HTTP request failed with error %s\n", err)
	}
	data, _ := ioutil.ReadAll(response.Body)
	fmt.Println(string(data))
	var location Location
	if err := json.Unmarshal(data, &location); err != nil {
		panic(err)
	}
	fmt.Println(location.Name)
}

What did you expect to see?
If this code was working correctly, my function would correctly unmarshal the JSON into a Location object and it would print out the name of the Location as specified in the JSON.

What did you see instead?
Instead, I am receiving the following error:

panic: json: cannot unmarshal bool into Go struct field Attribute.attributes.values of type structpb.Value

Which fails at the panic(err) line when unmarshaling.

Anything else we should know about your project / environment?
I am running this locally using the GoLand IDE

[puellanivis]

encoding/json does not understand anything of how to marshal from or unmarshal to golang/protobuf/ptype/struct.Value. The encoding/json library is specifically not supported for marshalling and unmarshalling protobuf data types, because the protobuf JSON mapping standards cannot be complied with through the encoding/json package.

[blakecschmidt]

@puellanivis Thanks for that information, this makes a lot of sense. I'm assuming this means I just need to use the protobuf jsonpb.Unmarshal() instead? I've been looking at it and am having a little trouble understanding in what way I need to change my code because the arguments seem to be a bit different than what the encoding/json unmarshal wants. Would you be able to shed some light on this for me?

[puellanivis]

The jsonpb package only knows how to unmarshal protobuf messages, and is not ever intended to unmarshal individual protobuf elements. This means you cannot integrate it into unmarshalling directly into a slice of protobuf objects, since protobuf does not have a concept of a slice outside of the body of a message.

You would likely need to use something like:

	Values []json.RawMessage `json:"values"`

And then jsobpb.Unmarshal each value individually, or define the whole Attribute struct as a protobuf Message somewhere, and then jsonpb.Unmarshal into that.

[blakecschmidt]

Thanks for the help, I'm probably gonna move forward with that json.RawMessage and if I run into further problems I may just need to set the entire thing as a protobuf message