API_il2cpp_domain_get_assemblies_hook.cs

using System;
using System.Runtime.InteropServices;
using Il2CppInterop.Runtime.Runtime;

namespace Il2CppInterop.Runtime.Injection.Hooks
{
    internal unsafe class API_il2cpp_domain_get_assemblies_hook : Hook<API_il2cpp_domain_get_assemblies_hook.MethodDelegate>
    {
        public override MethodDelegate GetDetour() => Hook;
        public override string TargetMethodName => "il2cpp_domain_get_assemblies";

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        internal delegate IntPtr MethodDelegate(IntPtr domain, long* size);

        private IntPtr currentDataPtr = IntPtr.Zero;
        private int lastAssemblyListSize = -1;

        private IntPtr Hook(IntPtr domain, long* size)
        {
            IntPtr assemblyArrayPtr = Original(domain, size);

            if (InjectorHelpers.InjectedImages.Count > 0)
            {
                CreateCustomAssemblyList((int)*size, assemblyArrayPtr);

                *size = lastAssemblyListSize;
                return currentDataPtr;
            }

            return assemblyArrayPtr;
        }

        private void CreateCustomAssemblyList(int origSize, IntPtr assemblyArrayPtr)
        {
            var newSize = origSize + InjectorHelpers.InjectedImages.Count;
            if (lastAssemblyListSize == newSize) return;

            Il2CppAssembly** oldArray = (Il2CppAssembly**)assemblyArrayPtr;

            if (currentDataPtr != IntPtr.Zero)
                Marshal.FreeHGlobal(currentDataPtr);

            currentDataPtr = Marshal.AllocHGlobal(newSize * sizeof(Il2CppSystem.IntPtr));
            Il2CppAssembly** newArray = (Il2CppAssembly**)currentDataPtr;

            int i;

            for (i = 0; i < origSize; i++)
                newArray[i] = oldArray[i];

            i = origSize;
            foreach (IntPtr imagePtr in InjectorHelpers.InjectedImages.Values)
            {
                var image = UnityVersionHandler.Wrap((Il2CppImage*)imagePtr);
                newArray[i] = image.Assembly;
                i++;
            }

            lastAssemblyListSize = newSize;
        }

        public override IntPtr FindTargetMethod()
        {
            return InjectorHelpers.GetIl2CppExport(nameof(IL2CPP.il2cpp_domain_get_assemblies));
        }
    }
}