Dalamud/Dalamud/Game/Network/Internal/WinSockHandlers.cs

using System;
using System.Net.Sockets;
using System.Runtime.InteropServices;

using Dalamud.Hooking;
using Dalamud.Hooking.Internal;

namespace Dalamud.Game.Network.Internal
{
    /// <summary>
    /// This class enables TCP optimizations in the game socket for better performance.
    /// </summary>
    internal sealed class WinSockHandlers : IDisposable
    {
        private Hook<SocketDelegate> ws2SocketHook;

        /// <summary>
        /// Initializes a new instance of the <see cref="WinSockHandlers"/> class.
        /// </summary>
        public WinSockHandlers()
        {
            this.ws2SocketHook = HookManager.DirtyLinuxUser ? null
                : Hook<SocketDelegate>.FromSymbol("ws2_32.dll", "socket", this.OnSocket, true);
            this.ws2SocketHook?.Enable();
        }

        [UnmanagedFunctionPointer(CallingConvention.Winapi)]
        private delegate IntPtr SocketDelegate(int af, int type, int protocol);

        /// <summary>
        /// Disposes of managed and unmanaged resources.
        /// </summary>
        public void Dispose()
        {
            this.ws2SocketHook?.Dispose();
        }

        private IntPtr OnSocket(int af, int type, int protocol)
        {
            var socket = this.ws2SocketHook.Original(af, type, protocol);

            // IPPROTO_TCP
            if (type == 1)
            {
                // INVALID_SOCKET
                if (socket != new IntPtr(-1))
                {
                    // In case you're not aware of it: (albeit you should)
                    // https://linux.die.net/man/7/tcp
                    // https://assets.extrahop.com/whitepapers/TCP-Optimization-Guide-by-ExtraHop.pdf
                    var value = new IntPtr(1);
                    _ = NativeFunctions.SetSockOpt(socket, SocketOptionLevel.Tcp, SocketOptionName.NoDelay, ref value, 4);

                    // Enable tcp_quickack option. This option is undocumented in MSDN but it is supported in Windows 7 and onwards.
                    value = new IntPtr(1);
                    _ = NativeFunctions.SetSockOpt(socket, SocketOptionLevel.Tcp, SocketOptionName.AddMembership, ref value, 4);
                }
            }

            return socket;
        }
    }
}