rpc: attempt to fix ping/pong logic race (#27733)

This should fix #27726. With enough load, it might happen that the SetPongHandler 
callback gets invoked before the call to SetReadDeadline is made in pingLoop. When 
this occurs, the socket will end up with a 30s read deadline even though it got the pong,
which will lead to a timeout.

The fix here is processing the pong on pingLoop, synchronizing with the code that 
sends the ping.

rpc/websocket.go

@@ -280,15 +280,11 @@ type websocketCodec struct {
 
 	wg           sync.WaitGroup
 	pingReset    chan struct{}
+	pongReceived chan struct{}
 }
 
 func newWebsocketCodec(conn *websocket.Conn, host string, req http.Header) ServerCodec {
 	conn.SetReadLimit(wsMessageSizeLimit)
-	conn.SetPongHandler(func(appData string) error {
-		conn.SetReadDeadline(time.Time{})
-		return nil
-	})
-
 	encode := func(v interface{}, isErrorResponse bool) error {
 		return conn.WriteJSON(v)
 	}
@@ -296,6 +292,7 @@ func newWebsocketCodec(conn *websocket.Conn, host string, req http.Header) Serve
 		jsonCodec:    NewFuncCodec(conn, encode, conn.ReadJSON).(*jsonCodec),
 		conn:         conn,
 		pingReset:    make(chan struct{}, 1),
+		pongReceived: make(chan struct{}),
 		info: PeerInfo{
 			Transport:  "ws",
 			RemoteAddr: conn.RemoteAddr().String(),
@@ -306,6 +303,13 @@ func newWebsocketCodec(conn *websocket.Conn, host string, req http.Header) Serve
 	wc.info.HTTP.Origin = req.Get("Origin")
 	wc.info.HTTP.UserAgent = req.Get("User-Agent")
 	// Start pinger.
+	conn.SetPongHandler(func(appData string) error {
+		select {
+		case wc.pongReceived <- struct{}{}:
+		case <-wc.closed():
+		}
+		return nil
+	})
 	wc.wg.Add(1)
 	go wc.pingLoop()
 	return wc
@@ -334,26 +338,31 @@ func (wc *websocketCodec) writeJSON(ctx context.Context, v interface{}, isError
 
 // pingLoop sends periodic ping frames when the connection is idle.
 func (wc *websocketCodec) pingLoop() {
-	var timer = time.NewTimer(wsPingInterval)
+	var pingTimer = time.NewTimer(wsPingInterval)
 	defer wc.wg.Done()
-	defer timer.Stop()
+	defer pingTimer.Stop()
 
 	for {
 		select {
 		case <-wc.closed():
 			return
+
 		case <-wc.pingReset:
-			if !timer.Stop() {
-				<-timer.C
+			if !pingTimer.Stop() {
+				<-pingTimer.C
 			}
-			timer.Reset(wsPingInterval)
-		case <-timer.C:
+			pingTimer.Reset(wsPingInterval)
+
+		case <-pingTimer.C:
 			wc.jsonCodec.encMu.Lock()
 			wc.conn.SetWriteDeadline(time.Now().Add(wsPingWriteTimeout))
 			wc.conn.WriteMessage(websocket.PingMessage, nil)
 			wc.conn.SetReadDeadline(time.Now().Add(wsPongTimeout))
 			wc.jsonCodec.encMu.Unlock()
-			timer.Reset(wsPingInterval)
+			pingTimer.Reset(wsPingInterval)
+
+		case <-wc.pongReceived:
+			wc.conn.SetReadDeadline(time.Time{})
 		}
 	}
 }