update example, optimize the time when data is first displayed

Author: mzzsfy

_example/fasthttp/main.go

@@ -37,7 +37,7 @@ func main() {
 	ws.HandleFunc("/debug/statsviz/ws", srv.Ws())
 
 	// Server start
-	go http.Serve(m.Match(cmux.HTTP1HeaderField("Upgrade", "websocket")), ws)
+	go http.Serve(m.Match(cmux.HTTP1HeaderField("Accept", "text/event-stream")), ws)
 	go fasthttp.Serve(m.Match(cmux.Any()), r.Handler)
 	fmt.Println("Point your browser to http://localhost:8083/debug/statsviz/")
 	m.Serve()

_example/fiber/main.go

@@ -43,7 +43,7 @@ func main() {
 	fmt.Println("Point your browser to http://localhost:8093/debug/statsviz/")
 
 	// Server start
-	go http.Serve(m.Match(cmux.HTTP1HeaderField("Upgrade", "websocket")), ws)
+	go http.Serve(m.Match(cmux.HTTP1HeaderField("Accept", "text/event-stream")), ws)
 	go app.Listener(m.Match(cmux.Any()))
 	m.Serve()
 }

statsviz.go

@@ -296,12 +296,33 @@ func (s *Server) startTransfer(w io.Writer) {
 	<-c
 }
 func (s *Server) callData() {
+	{
+		//the first time it was sent immediately
+		buffer := bytes.Buffer{}
+		buffer.WriteString("data: ")
+		if err := s.plots.WriteValues(&buffer); err == nil {
+			buffer.WriteString("\n\n")
+			err = s.onData[0](buffer.Bytes())
+			if err != nil {
+				s.lock.Lock()
+				if len(s.onData) == 1 {
+					s.onData = nil
+					s.lock.Unlock()
+					return
+				} else {
+					s.onData = s.onData[1:]
+				}
+				s.lock.Unlock()
+			}
+		}
+	}
 	tick := time.NewTicker(s.intv)
 	defer tick.Stop()
 	for range tick.C {
 		buffer := bytes.Buffer{}
 		buffer.WriteString("data: ")
 		if err := s.plots.WriteValues(&buffer); err != nil {
+			//maybe all connections should be closed?
 			//fmt.Println("Error plots.WriteValues:", err)
 			continue
 		}