Eventsource golang : how to detect client disconnection ?

sse.go

func (sh StreamHandler) ServeHTTP(resp http.ResponseWriter, req *http.Request) {

	es := eventsource.New(
		&eventsource.Settings{
			Timeout:        2 * time.Second,
			CloseOnTimeout: true,
			IdleTimeout:    2 * time.Second,
			Gzip:           true,
		},
		func(req *http.Request) [][]byte {
			return [][]byte{
				[]byte("X-Accel-Buffering: no"),
				[]byte("Access-Control-Allow-Origin: *"),
			}
		},
	)

	es.ServeHTTP(resp, req)

	go func() {
		var id int
		for {
			id++
			time.Sleep(1 * time.Second)
			es.SendEventMessage("blabla", "message", strconv.Itoa(id))
		}
	}()

}