Publishing to google pub sub asynchronously through goroutine - google-app-engine

Question

I'm trying to push the message to google pub-sub asynchronously through goroutine but I'm facing below error
panic: not an App Engine context
I'm using mux and have an api handler
n = 1 million
func apihandler(w http.ResponseWriter, r *http.Request) {
go createuniquecodes(n)
return "request running in background"
}
func createuniquecodes(n) {
c := make(chan string)
go createuniquecodes(c, n)
for val := range c {
publishtopubsub(val)
}
}
func createuniquecodes(n) {
for i := 0; i < n; i++ {
uniquecode := some random string
// publish to channel and pubsub
c <- uniquecode
}
close(c)
}
func publishuq(msg string) error {
ctx := context.Background()
client, err := pubsub.NewClient(ctx, projectId)
if err != nil {
log.Fatalf("Could not create pubsub Client: %v", err)
}
t := client.Topic(topicName)
result := t.Publish(ctx, &pubsub.Message{
Data: []byte(msg),
})
id, err := result.Get(ctx)
if err != nil {
return err
}
fmt.Printf("Published a message; msg ID: %v\n", id)
return nil
}
Please note that I need to generate 5 million unique codes,
How will I define a context in go routine since I'm doing everything asynchronously

Answer 1

I assume you're using the App Engine standard (not flexible) environment. Please note that a "request handler (apihandler in your case) has a limited amount of time to generate and return a response to a request, typically around 60 seconds. Once the deadline has been reached, the request handler is interrupted".
You're trying to "break out" of the request when calling go createuniquecodes(n) and then ctx := context.Background() down the line is what panics with not an App Engine context. You could technically use NewContext(req *http.Request) to derive a valid context from the original context, but again, you'd only have 60s before your request times out.
Please have a look at TaskQueues, as they " let applications perform work, called tasks, asynchronously outside of a user request."