Unmarshall PubSub Request Data []bytes with Go - json

Question

I have an end-point that receives data from a Google PubSub request. As per this repo, the object is as so:
type pushRequest struct {
Message struct {
Attributes map[string]string
Data []byte
ID string `json:"message_id"`
}
Subscription string
}
The Data field is consistently formatted as so:
type Data struct {
Key string `json:"key"`
Body string `json:"body"`
Meta map[string]interface{} `json:"meta"`
}
I can obviously unmarshal the JSON request with something like this:
f := &pushRequest{}
json.Unmarshal(msg, &f)
That leaves with the the []bytes field. Which I can do something like this to convert to a string, as per the docs
messages = append(messages, string(f.Message.Data))
Which doesn't help, since I need it as a struct.
I can Unmarshal the array again:
var m Data
json.Unmarshal(f.Message.Data, &m)
Have tried changing the field type in the pushRequest struct to Data without success. Blank...
Is there a way I can unpack things in a single pass? Doing it twice seems ridiculous.
If it's obvious, I just can't see it!

Answer 1

decoder := json.NewDecoder(r.Body)
psmsg := &PushRequest{}
decoderErr := decoder.Decode(&psmsg)
if decoderErr != nil {
// Error...
return
}
data := Data{}
unmarshalErr := json.Unmarshal([]byte(string(psmsg.Message.Data)), &data)
if unmarshalErr != nil {
// Error...
return
}

Answer 2

Here is a snippet from my cloud function, which serves as a pub/sub push endpoint. The key is that you first have to decode the body using the PushRequest struct. Next, you can transform the message data into a struct. According to the documentation, the Data field within Message is a base-64 encoded string, therefore you have to decode it first.
type PushRequest struct {
Message pubsub.PubsubMessage `json:"message"`
Subscription string `json:"subscription"`
}
type Example struct {
ID string `json:"id" firestore:"id"`
}
func HTTPEndpoint(w http.ResponseWriter, r *http.Request) {
var pr common.PushRequest
if err := json.NewDecoder(r.Body).Decode(&pr); err != nil {
log.Fatalf("Could not decode body: %v", err)
return
}
data, err := base64.StdEncoding.DecodeString(pr.Message.Data)
if err != nil {
log.Fatalf("Base64: %v", err)
return
}
var example Example
if err := json.Unmarshal(data, &example); err != nil {
log.Fatalf("Json: %v", err)
return
}
// Do something useful with the struct
}