Add NetworkLagDriver for lag simulation over low-level network transport layer

Source/Engine/Networking/Drivers/NetworkLagDriver.h

@@ -0,0 +1,77 @@
+// Copyright (c) 2012-2022 Wojciech Figat. All rights reserved.
+
+#pragma once
+
+#include "Engine/Networking/INetworkDriver.h"
+#include "Engine/Networking/NetworkMessage.h"
+#include "Engine/Networking/NetworkConnection.h"
+#include "Engine/Networking/NetworkEvent.h"
+#include "Engine/Scripting/ScriptingObject.h"
+#include "Engine/Core/Collections/Array.h"
+
+/// <summary>
+/// Low-level network transport interface implementation that is proxy of another nested INetworkDriver implementation but with lag simulation feature.
+/// </summary>
+API_CLASS(Namespace="FlaxEngine.Networking", Sealed) class FLAXENGINE_API NetworkLagDriver : public ScriptingObject, public INetworkDriver
+{
+    DECLARE_SCRIPTING_TYPE(NetworkLagDriver);
+
+private:
+    struct LagMessage
+    {
+        double Lag;
+        int32 Type;
+        NetworkChannelType ChannelType;
+        NetworkMessage Message;
+        NetworkConnection Target;
+        Array<NetworkConnection> Targets;
+        Array<byte> MessageData; // TODO: use message buffers cache (of size config.MessageSize) to reduce dynamic memory allocations
+    };
+    struct LagEvent
+    {
+        double Lag;
+        NetworkEvent Event;
+    };
+
+    INetworkDriver* _driver = nullptr;
+    Array<LagMessage> _messages;
+    Array<LagEvent> _events;
+
+public:
+    ~NetworkLagDriver();
+
+    /// <summary>
+    /// Network lag value in milliseconds. Adds a delay between sending and receiving messages (2 * Lag is TTL).
+    /// </summary>
+    API_FIELD() float Lag = 100.0f;
+
+    /// <summary>
+    /// Gets or sets the nested INetworkDriver to use as a proxy with lags.
+    /// </summary>
+    API_PROPERTY() INetworkDriver* GetDriver() const
+    {
+        return _driver;
+    }
+
+    /// <summary>
+    /// Gets or sets the nested INetworkDriver to use as a proxy with lags.
+    /// </summary>
+    API_PROPERTY() void SetDriver(INetworkDriver* value);
+
+public:
+    // [INetworkDriver]
+    String DriverName() override;
+    bool Initialize(NetworkPeer* host, const NetworkConfig& config) override;
+    void Dispose() override;
+    bool Listen() override;
+    bool Connect() override;
+    void Disconnect() override;
+    void Disconnect(const NetworkConnection& connection) override;
+    bool PopEvent(NetworkEvent* eventPtr) override;
+    void SendMessage(NetworkChannelType channelType, const NetworkMessage& message) override;
+    void SendMessage(NetworkChannelType channelType, const NetworkMessage& message, NetworkConnection target) override;
+    void SendMessage(NetworkChannelType channelType, const NetworkMessage& message, const Array<NetworkConnection, HeapAllocation>& targets) override;
+
+private:
+    void OnUpdate();
+};