Setting up Gmail Push notifications through GCP pub/sub using Go - go

Question

I'm looking to basically setup my application such that it receives notifications every time a mail hits a Gmail inbox.
I'm following the guide here.
I have a Topic and subscription created.
My credentials are working. I can retrieve my emails using the credentials and a Go script as shown here.
I have enabled permissions on my topic gmail with gmail-api-push#system.gserviceaccount.com as a Pub/Sub Publisher.
I have tested the topic in pub/sub by manually sending a message through the console. The message shows up in the simple subscription I made.
main.go
func main() {
ctx := context.Background()
// Sets your Google Cloud Platform project ID.
projectID := "xxx"
// Creates a client.
// client, err := pubsub.NewClient(ctx, projectID)
_, err := pubsub.NewClient(ctx, projectID)
if err != nil {
log.Fatalf("Failed to create client: %v", err)
}
b, err := ioutil.ReadFile("credentials.json")
if err != nil {
log.Fatalf("Unable to read client secret file: %v", err)
}
// If modifying these scopes, delete your previously saved token.json.
config, err := google.ConfigFromJSON(b, gmail.GmailReadonlyScope)
if err != nil {
log.Fatalf("Unable to parse client secret file to config: %v", err)
}
gmailClient := getClient(config)
svc, err := gmail.New(gmailClient)
if err != nil {
log.Fatalf("Unable to retrieve Gmail client: %v", err)
}
var watchRequest gmail.WatchRequest
watchRequest.TopicName = "projects/xxx/topics/gmail"
svc.Users.Watch("xxx#gmail.com", &watchRequest)
...
The script runs fine although there's no stdout with any confirmation the Watch service is running.
However, with the above setup, I sent a mail from xxx#gmail.com to itself but the mail does not show up in my topic/subscription.
What else must I do to enable Gmail push notification through pub/sub using Go?

Answer 1

Make sure you are calling the Do method on your UsersWatchCall. The svc.Users.Watch returns only the structure, doesn't do the call immediately.
It would look something like this:
res, err := svc.Users.Watch("xxx#gmail.com", &watchRequest).Do()
if err != nil {
// don't forget to check the error
}