quantum-space-buddies/FizzyFacepunch/NextCommon.cs

using Mirror;
using Steamworks;
using Steamworks.Data;
using System;
using System.Runtime.InteropServices;
using UnityEngine;

public abstract class NextCommon
{
    protected const int MAX_MESSAGES = 256;

    protected Result SendSocket(Connection conn, byte[] data, int channelId)
    {
        Array.Resize(ref data, data.Length + 1);
        data[data.Length - 1] = (byte)channelId;

        GCHandle pinnedArray = GCHandle.Alloc(data, GCHandleType.Pinned);
        IntPtr pData = pinnedArray.AddrOfPinnedObject();
        SendType sendFlag = channelId == Channels.Unreliable ? SendType.Unreliable : SendType.Reliable;
        Result res = conn.SendMessage(pData, data.Length, sendFlag);
        if (res != Result.OK)
        {
            Debug.LogWarning($"Send issue: {res}");
        }

        pinnedArray.Free();
        return res;
    }

    protected (byte[], int) ProcessMessage(IntPtr ptrs, int size)
    {
        byte[] managedArray = new byte[size];
        Marshal.Copy(ptrs, managedArray, 0, size);
        int channel = managedArray[managedArray.Length - 1];
        Array.Resize(ref managedArray, managedArray.Length - 1);
        return (managedArray, channel);
    }
}