Reduce VPN control packet latency

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

@@ -76,6 +76,46 @@ func TestGatewayUploadPrioritizesTCPControlPackets(t *testing.T) {
 	}
 }
 
+func TestGatewayUploadMicroBatchesTCPControlPackets(t *testing.T) {
+	transport := &recordingGatewayTransport{}
+	gateway := &Gateway{Transport: transport, VPNConnectionID: "vpn-1"}
+	priorityPackets := make(chan []byte, 2)
+	packets := make(chan []byte, 1)
+
+	first := testIPv4TCPPacket([4]byte{192, 168, 200, 95}, [4]byte{10, 77, 0, 2}, 3389, 51000)
+	first[33] = 0x12
+	second := testIPv4TCPPacket([4]byte{188, 40, 167, 82}, [4]byte{10, 77, 0, 2}, 80, 51002)
+	second[33] = 0x12
+	priorityPackets <- first
+	priorityPackets <- second
+
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan error, 1)
+	go func() {
+		done <- gateway.uploadGatewayPackets(ctx, priorityPackets, packets)
+	}()
+	defer func() {
+		cancel()
+		<-done
+	}()
+
+	deadline := time.After(time.Second)
+	for {
+		if batch := transport.firstBatch(); len(batch) == 2 {
+			if string(batch[0]) != string(first) || string(batch[1]) != string(second) {
+				t.Fatalf("priority batch = %#v, want both control packets in order", batch)
+			}
+			return
+		}
+		select {
+		case <-deadline:
+			t.Fatal("timed out waiting for priority microbatch")
+		default:
+			time.Sleep(time.Millisecond)
+		}
+	}
+}
+
 func TestIsTCPControlPacket(t *testing.T) {
 	packet := testIPv4TCPPacket([4]byte{192, 168, 200, 95}, [4]byte{10, 77, 0, 2}, 3389, 51000)
 	if isTCPControlPacket(packet) {