onSubscribe send a message to the subscriber

[Cyliann]

Is it possible to send a message to the subscriber as soon as it subscribes? I need to send an ID to every new client connected.
Sadly, this doesn't work:

func main() {
        server := sse.New()
	mux := http.NewServeMux()
	mux.HandleFunc("/events", eventHandler)

	http.ListenAndServe(":8080", mux)
}

func eventHandler(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Message"))
	w.(http.Flusher).Flush()

	server.ServeHTTP(w, r)
}

I though that onSubsrcibe() can to that, but it doesn't allow passing http.ResponseWriter in any way and I can't see how it can be accomplished otherwise.
I've been banging my head over the wall for the past 2 days and I can't get it to work.
Could you provide any help?

[Prasannakumar414]

Hello @Cyliann you can add the headers to keep connection alive and connection type to event stream.
For SSE connection we must have following things

• Connection as keep-alive
• Connection Type to be text/event-stream

func main() {
        server := sse.New()
	mux := http.NewServeMux()
	mux.HandleFunc("/events", eventHandler)

	http.ListenAndServe(":8080", mux)
}

func eventHandler(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.Write([]byte("Message"))
	w.(http.Flusher).Flush()

	server.ServeHTTP(w, r)
}

I have implemented something like this and it is working for me

mux.HandleFunc("/events", func(w http.ResponseWriter, r *http.Request) {
		go func() {
			<-r.Context().Done()
			done <- true
			println("The client is disconnected here")
		}()
		w.Header().Set("Content-Type", "text/event-stream")
		w.Header().Set("Cache-Control", "no-cache")
		w.Header().Set("Connection", "keep-alive")
		rc := http.NewResponseController(w)
		_, err := fmt.Fprintf(w, "data:congo on entering to sse\n\n")
		if err != nil {
			return
		}
		err = rc.Flush()
		if err != nil {
			return
		}

		server.ServeHTTP(w, r)
	})