go - Unmarshalling a JSON that may or may not return an array?

Question

I'm retrieving JSON from a third party website (home electricity usage), and depending on what I've requested from the site, the JSON returned may or may not be an array. For example, if I request a list of my smart meters, I get this (results truncated, due to large size):

{"gwrcmds":{"gwrcmd":{"gcmd":"SPA_UserGetSmartMeterList","gdata":{"gip":{"version":"1"...

Where gwrcmd is a single element.

But if I request electricity usage for the last half hour, I get this:

{"gwrcmds":{"gwrcmd":[{"gcmd":"DeviceGetChart","gdata":{"gip":{"version":"1" ...

See how gwrcmd is now an array?

Within my Go app, I have a struct that looks like this (again, truncated, as it goes on for a while. There's more sub-structs and properties beneath "Version":

type Response struct {
    Gwrcmds struct {
        Gwrcmd struct {
            Gcmd  string
            Gdata struct {
                Gip struct {
                    Version string

If gwrcmd is an array, Gwrcmd needs to be a []struct { }, but if it's not, it's just a regular old struct { }

The problem is that json.Unmarshal just returns an error if the JSON has an array and the struct does not have a slice (or vice versa).

Would I need to create a second struct that duplicates the first one (except with a []struct { } instead), or is there a better way to do it? I thought of something with interfaces, but I haven't really touched those yet, so I'm not 100% sure on them.

Answer 1

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