Reduce VPN control packet latency

agents/rap-node-agent/internal/vpnruntime/gateway.go

@@ -51,6 +51,7 @@ const (
 	vpnGatewayBatchMaxPackets   = 2048
 	vpnGatewayBatchMaxBytes     = 8 * 1024 * 1024
 	vpnGatewayBatchFlushTimeout = 3 * time.Millisecond
+	vpnGatewayPriorityBatchWait = 20 * time.Millisecond
 )
 
 type readWriteCloser interface {
@@ -350,9 +351,34 @@ func (g *Gateway) uploadGatewayPackets(ctx context.Context, priorityPackets <-ch
 	}
 	flushPriority := func(packet []byte) {
 		flush()
-		if addPacket(packet) {
-			flush()
+		if !addPacket(packet) {
+			return
 		}
+		deadline := time.Now().Add(vpnGatewayPriorityBatchWait)
+		for len(batch) < vpnGatewayBatchMaxPackets && batchBytes < vpnGatewayBatchMaxBytes {
+			wait := time.Until(deadline)
+			if wait <= 0 {
+				break
+			}
+			timer := time.NewTimer(wait)
+			select {
+			case next := <-priorityPackets:
+				if !timer.Stop() {
+					select {
+					case <-timer.C:
+					default:
+					}
+				}
+				if !addPacket(next) {
+					flush()
+					_ = addPacket(next)
+				}
+			case <-timer.C:
+				flush()
+				return
+			}
+		}
+		flush()
 	}
 	for {
 		if len(batch) == 0 && timerActive {