Penumbra/Penumbra/Interop/ResourceLoading/CreateFileWHook.cs

using Dalamud.Hooking;
using Dalamud.Plugin.Services;
using Penumbra.String;
using Penumbra.String.Classes;
using Penumbra.String.Functions;

namespace Penumbra.Interop.ResourceLoading;

/// <summary>
/// To allow XIV to load files of arbitrary path length,
/// we use the fixed size buffers of their formats to only store pointers to the actual path instead.
/// Then we translate the stored pointer to the path in CreateFileW, if the prefix matches.
/// </summary>
public unsafe class CreateFileWHook : IDisposable
{
    public const int RequiredSize = 28;

    public CreateFileWHook(IGameInteropProvider interop)
    {
        _createFileWHook = interop.HookFromImport<CreateFileWDelegate>(null, "KERNEL32.dll", "CreateFileW", 0, CreateFileWDetour);
        _createFileWHook.Enable();
    }

    /// <summary>
    /// Write the data read specifically in the CreateFileW hook to a buffer array.
    /// </summary>
    /// <param name="buffer">The buffer the data is written to.</param>
    /// <param name="address">The pointer to the UTF8 string containing the path.</param>
    /// <param name="length">The length of the path in bytes.</param>
    public static void WritePtr(char* buffer, byte* address, int length)
    {
        // Set the prefix, which is not valid for any actual path.
        buffer[0] = Prefix;

        var ptr = (byte*)buffer;
        var v   = (ulong)address;
        var l   = (uint)length;

        // Since the game calls wstrcpy without a length, we need to ensure
        // that there is no wchar_t (i.e. 2 bytes) of 0-values before the end.
        // Fill everything with 0xFF and use every second byte.
        MemoryUtility.MemSet(ptr + 2, 0xFF, 23);

        // Write the byte pointer.
        ptr[2]  = (byte)(v >> 0);
        ptr[4]  = (byte)(v >> 8);
        ptr[6]  = (byte)(v >> 16);
        ptr[8]  = (byte)(v >> 24);
        ptr[10] = (byte)(v >> 32);
        ptr[12] = (byte)(v >> 40);
        ptr[14] = (byte)(v >> 48);
        ptr[16] = (byte)(v >> 56);

        // Write the length.
        ptr[18] = (byte)(l >> 0);
        ptr[20] = (byte)(l >> 8);
        ptr[22] = (byte)(l >> 16);
        ptr[24] = (byte)(l >> 24);

        ptr[RequiredSize - 2] = 0;
        ptr[RequiredSize - 1] = 0;
    }

    public void Dispose()
    {
        _createFileWHook.Disable();
        _createFileWHook.Dispose();
        foreach (var ptr in _fileNameStorage.Values)
            Marshal.FreeHGlobal(ptr);
    }

    /// <remarks> Long paths in windows need to start with "\\?\", so we keep this static in the pointers. </remarks>
    private static nint SetupStorage()
    {
        var ptr = (char*)Marshal.AllocHGlobal(2 * BufferSize);
        ptr[0] = '\\';
        ptr[1] = '\\';
        ptr[2] = '?';
        ptr[3] = '\\';
        ptr[4] = '\0';
        return (nint)ptr;
    }

    // The prefix is not valid for any actual path, so should never run into false-positives.
    private const char Prefix     = (char)((byte)'P' | (('?' & 0x00FF) << 8));
    private const int  BufferSize = Utf8GamePath.MaxGamePathLength;

    private delegate nint CreateFileWDelegate(char* fileName, uint access, uint shareMode, nint security, uint creation, uint flags,
        nint template);

    private readonly Hook<CreateFileWDelegate> _createFileWHook;

    /// <summary> Some storage to skip repeated allocations. </summary>
    private readonly ThreadLocal<nint> _fileNameStorage = new(SetupStorage, true);

    private nint CreateFileWDetour(char* fileName, uint access, uint shareMode, nint security, uint creation, uint flags, nint template)
    {
        // Translate data if prefix fits.
        if (CheckPtr(fileName, out var name))
        {
            // Use static storage.
            var ptr = WriteFileName(name);
            Penumbra.Log.Verbose($"[ResourceHooks] Calling CreateFileWDetour with {ByteString.FromSpanUnsafe(name, false)}.");
            return _createFileWHook.OriginalDisposeSafe(ptr, access, shareMode, security, creation, flags, template);
        }

        return _createFileWHook.OriginalDisposeSafe(fileName, access, shareMode, security, creation, flags, template);
    }


    /// <remarks>Write the UTF8-encoded byte string as UTF16 into the static buffers,
    /// replacing any forward-slashes with back-slashes and adding a terminating null-wchar_t.</remarks>
    private char* WriteFileName(ReadOnlySpan<byte> actualName)
    {
        var span    = new Span<char>((char*)_fileNameStorage.Value + 4, BufferSize - 4);
        var written = Encoding.UTF8.GetChars(actualName, span);
        for (var i = 0; i < written; ++i)
        {
            if (span[i] == '/')
                span[i] = '\\';
        }

        span[written] = '\0';

        return (char*)_fileNameStorage.Value;
    }

    private static bool CheckPtr(char* buffer, out ReadOnlySpan<byte> fileName)
    {
        if (buffer[0] is not Prefix)
        {
            fileName = ReadOnlySpan<byte>.Empty;
            return false;
        }

        var ptr = (byte*)buffer;

        // Read the byte pointer.
        var address = 0ul;
        address |= (ulong)ptr[2] << 0;
        address |= (ulong)ptr[4] << 8;
        address |= (ulong)ptr[6] << 16;
        address |= (ulong)ptr[8] << 24;
        address |= (ulong)ptr[10] << 32;
        address |= (ulong)ptr[12] << 40;
        address |= (ulong)ptr[14] << 48;
        address |= (ulong)ptr[16] << 56;

        // Read the length.
        var length = 0u;
        length |= (uint)ptr[18] << 0;
        length |= (uint)ptr[20] << 8;
        length |= (uint)ptr[22] << 16;
        length |= (uint)ptr[24] << 24;

        fileName = new ReadOnlySpan<byte>((void*)address, (int)length);
        return true;
    }

    // ***** Old method *****

    //[DllImport( "kernel32.dll" )]
    //private static extern nint LoadLibrary( string dllName );
    //
    //[DllImport( "kernel32.dll" )]
    //private static extern nint GetProcAddress( nint hModule, string procName );
    //
    //public CreateFileWHookOld()
    //{
    //    var userApi           = LoadLibrary( "kernel32.dll" );
    //    var createFileAddress = GetProcAddress( userApi, "CreateFileW" );
    //    _createFileWHook = Hook<CreateFileWDelegate>.FromAddress( createFileAddress, CreateFileWDetour );
    //}
}