Introduce DirectPlay passthrough

The wrapper now checks for the existence of a "real" dplayx.dll
circumventing the Windows missing dependencies prompt.
If real dplayx.dll is found, it will pass through to that,
so users who have DirectPlay installed can now play online
without having to delete files from the game directory.

source/VersionInfo.lua

@@ -1,7 +1,7 @@
 defines { 
     "rsc_FullName=\"DirectPlay Stub\"",
-    "rsc_MinorVersion=0",
+    "rsc_MinorVersion=1",
     "rsc_RevisionID=1",
     "rsc_BuildID=0",
-    "rsc_Copyright=\"2023\""
+    "rsc_Copyright=\"2023-2024\""
 }

source/dplayx.def

@@ -1,8 +1,9 @@
 LIBRARY DPLAYX
 EXPORTS
-	DirectPlayCreate=DirectPlayCreate_Stub @1
-	DirectPlayEnumerateA=DirectPlayEnumerate_Stub @2
-	DirectPlayEnumerateW=DirectPlayEnumerate_Stub @3
-	DirectPlayLobbyCreateA=DirectPlayLobbyCreate_Stub @4
-	DirectPlayLobbyCreateW=DirectPlayLobbyCreate_Stub @5
-	DirectPlayEnumerate=DirectPlayEnumerate_Stub @9
+	DirectPlayCreate @1
+	DirectPlayEnumerateA @2
+	DirectPlayEnumerateW @3
+	DirectPlayLobbyCreateA @4
+	DirectPlayLobbyCreateW @5
+	DirectPlayEnumerate @9
+	gdwDPlaySPRefCount @11

source/dplayx/dplayx.cpp

@@ -3,49 +3,88 @@
 
 #include <windows.h>
 #include <combaseapi.h>
+#include <ShlObj.h>
 
-#include "../dplay-stub.h"
+#include "../exportChecker.h"
+#include "stubs.h"
 
-HRESULT WINAPI DirectPlayCreate_Stub(LPGUID lpGUID, LPVOID* lplpDP, IUnknown* lpUnk)
+#include <filesystem>
+#include <mutex>
+
+static auto DirectPlayCreate_Func = &DirectPlayCreate_Stub;
+static auto DirectPlayEnumerate_Func = &DirectPlayEnumerate_Stub;
+static auto DirectPlayEnumerateA_Func = &DirectPlayEnumerate_Stub;
+static auto DirectPlayEnumerateW_Func = &DirectPlayEnumerate_Stub;
+static auto DirectPlayLobbyCreateA_Func = &DirectPlayLobbyCreate_Stub;
+static auto DirectPlayLobbyCreateW_Func = &DirectPlayLobbyCreate_Stub;
+
+static std::once_flag TryPassthroughFlag;
+static void DoTryPassthrough()
 {
-	if (lpUnk != nullptr)
-	{
-		return CLASS_E_NOAGGREGATION;
-	}
-	if (lpGUID == nullptr || lplpDP == nullptr)
+	PWSTR system32Path = nullptr;
+	if (SUCCEEDED(SHGetKnownFolderPath(FOLDERID_System, KF_FLAG_DEFAULT, nullptr, &system32Path)))
 	{
-		return DPERR_INVALIDPARAM;
+		const std::filesystem::path dllPath(std::filesystem::path(system32Path) / L"dplayx.dll");
+		if (CheckExports(dllPath.c_str(), {
+				"DirectPlayCreate", "DirectPlayEnumerate", "DirectPlayEnumerateA", "DirectPlayEnumerateW", "DirectPlayLobbyCreateA", "DirectPlayLobbyCreateW"
+			}))
+		{
+			HMODULE systemDplay = LoadLibraryW(dllPath.c_str());
+			if (systemDplay != nullptr)
+			{
+				DirectPlayCreate_Func = reinterpret_cast<decltype(DirectPlayCreate_Func)>(GetProcAddress(systemDplay, "DirectPlayCreate"));
+				DirectPlayEnumerate_Func = reinterpret_cast<decltype(DirectPlayEnumerate_Func)>(GetProcAddress(systemDplay, "DirectPlayEnumerate"));
+				DirectPlayEnumerateA_Func = reinterpret_cast<decltype(DirectPlayEnumerateA_Func)>(GetProcAddress(systemDplay, "DirectPlayEnumerateA"));
+				DirectPlayEnumerateW_Func = reinterpret_cast<decltype(DirectPlayEnumerateW_Func)>(GetProcAddress(systemDplay, "DirectPlayEnumerateW"));
+				DirectPlayLobbyCreateA_Func = reinterpret_cast<decltype(DirectPlayLobbyCreateA_Func)>(GetProcAddress(systemDplay, "DirectPlayLobbyCreateA"));
+				DirectPlayLobbyCreateW_Func = reinterpret_cast<decltype(DirectPlayLobbyCreateW_Func)>(GetProcAddress(systemDplay, "DirectPlayLobbyCreateW"));
+
+				// "Leak" the DLL handle on purpose
+			}
+		}
+
+		CoTaskMemFree(system32Path);
 	}
+}
 
-	*lplpDP = nullptr;
-	return DPERR_UNSUPPORTED;
+static void TryPassthrough()
+{
+	std::call_once(TryPassthroughFlag, DoTryPassthrough);
 }
 
-HRESULT WINAPI DirectPlayEnumerate_Stub(LPVOID lpEnumCallback, LPVOID /*lpContext*/)
+
+HRESULT WINAPI DirectPlayCreate(LPGUID lpGUID, LPVOID* lplpDP, IUnknown* lpUnk)
 {
-	if (lpEnumCallback == nullptr)
-	{
-		return DPERR_INVALIDPARAM;
-	}
-	return DP_OK;
+	TryPassthrough();
+	return DirectPlayCreate_Func(lpGUID, lplpDP, lpUnk);
 }
 
-HRESULT WINAPI DirectPlayLobbyCreate_Stub(LPGUID lpGUIDDSP, LPVOID* lplpDPL, IUnknown* lpUnk, void* lpData, DWORD dwDataSize)
+HRESULT WINAPI DirectPlayEnumerate(LPVOID lpEnumCallback, LPVOID lpContext)
 {
-	if (lpGUIDDSP != nullptr && *lpGUIDDSP != GUID_NULL)
-	{
-		return DPERR_INVALIDPARAM;
-	}
-	if (lpUnk != nullptr)
-	{
-		return CLASS_E_NOAGGREGATION;
-	}
-	if (lpData != nullptr || dwDataSize != 0)
-	{
-		return DPERR_INVALIDPARAM;
-	}
+	TryPassthrough();
+	return DirectPlayEnumerate_Func(lpEnumCallback, lpContext);
+}
+
+HRESULT WINAPI DirectPlayEnumerateA(LPVOID lpEnumCallback, LPVOID lpContext)
+{
+	TryPassthrough();
+	return DirectPlayEnumerateA_Func(lpEnumCallback, lpContext);
+}
 
-	// lplpDPL is not checked for validity in the real DLL...
-	*lplpDPL = nullptr;
-	return DPERR_UNSUPPORTED;
+HRESULT WINAPI DirectPlayEnumerateW(LPVOID lpEnumCallback, LPVOID lpContext)
+{
+	TryPassthrough();
+	return DirectPlayEnumerateW_Func(lpEnumCallback, lpContext);
+}
+
+HRESULT WINAPI DirectPlayLobbyCreateA(LPGUID lpGUIDDSP, LPVOID* lplpDPL, IUnknown* lpUnk, void* lpData, DWORD dwDataSize)
+{
+	TryPassthrough();
+	return DirectPlayLobbyCreateA_Func(lpGUIDDSP, lplpDPL, lpUnk, lpData, dwDataSize);
+}
+
+HRESULT WINAPI DirectPlayLobbyCreateW(LPGUID lpGUIDDSP, LPVOID* lplpDPL, IUnknown* lpUnk, void* lpData, DWORD dwDataSize)
+{
+	TryPassthrough();
+	return DirectPlayLobbyCreateW_Func(lpGUIDDSP, lplpDPL, lpUnk, lpData, dwDataSize);
 }

source/dplayx/stubs.cpp

@@ -0,0 +1,47 @@
+#include "stubs.h"
+
+HRESULT WINAPI DirectPlayCreate_Stub(LPGUID lpGUID, LPVOID* lplpDP, IUnknown* lpUnk)
+{
+	if (lpUnk != nullptr)
+	{
+		return CLASS_E_NOAGGREGATION;
+	}
+	if (lpGUID == nullptr || lplpDP == nullptr)
+	{
+		return DPERR_INVALIDPARAM;
+	}
+
+	*lplpDP = nullptr;
+	return DPERR_UNSUPPORTED;
+}
+
+HRESULT WINAPI DirectPlayEnumerate_Stub(LPVOID lpEnumCallback, LPVOID /*lpContext*/)
+{
+	if (lpEnumCallback == nullptr)
+	{
+		return DPERR_INVALIDPARAM;
+	}
+	return DP_OK;
+}
+
+HRESULT WINAPI DirectPlayLobbyCreate_Stub(LPGUID lpGUIDDSP, LPVOID* lplpDPL, IUnknown* lpUnk, void* lpData, DWORD dwDataSize)
+{
+	if (lpGUIDDSP != nullptr && *lpGUIDDSP != GUID_NULL)
+	{
+		return DPERR_INVALIDPARAM;
+	}
+	if (lpUnk != nullptr)
+	{
+		return CLASS_E_NOAGGREGATION;
+	}
+	if (lpData != nullptr || dwDataSize != 0)
+	{
+		return DPERR_INVALIDPARAM;
+	}
+
+	// lplpDPL is not checked for validity in the real DLL...
+	*lplpDPL = nullptr;
+	return DPERR_UNSUPPORTED;
+}
+
+DWORD gdwDPlaySPRefCount = 0;

source/dplayx/stubs.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+
+#include <windows.h>
+#include <combaseapi.h>
+
+#include "../dplay-stub.h"
+
+HRESULT WINAPI DirectPlayCreate_Stub(LPGUID lpGUID, LPVOID* lplpDP, IUnknown* lpUnk);
+HRESULT WINAPI DirectPlayEnumerate_Stub(LPVOID lpEnumCallback, LPVOID /*lpContext*/);
+HRESULT WINAPI DirectPlayLobbyCreate_Stub(LPGUID lpGUIDDSP, LPVOID* lplpDPL, IUnknown* lpUnk, void* lpData, DWORD dwDataSize);

source/exportChecker.cpp

@@ -0,0 +1,42 @@
+#include "exportChecker.h"
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+
+#include <windows.h>
+
+#include <vector>
+
+bool CheckExports(const wchar_t* path, std::initializer_list<std::string_view> exports)
+{
+	std::vector<std::string_view> exportsToCheck(exports);
+
+	HMODULE file = LoadLibraryExW(path, nullptr, LOAD_LIBRARY_AS_IMAGE_RESOURCE);
+	if (file != nullptr)
+	{
+		DWORD_PTR instance = reinterpret_cast<DWORD_PTR>(file) & ~3;
+		const PIMAGE_NT_HEADERS ntHeader = reinterpret_cast<PIMAGE_NT_HEADERS>(instance + reinterpret_cast<PIMAGE_DOS_HEADER>(instance)->e_lfanew);
+		const DWORD exportVA = ntHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress;
+		if (exportVA != 0)
+		{
+			const PIMAGE_EXPORT_DIRECTORY exportDirectory = reinterpret_cast<PIMAGE_EXPORT_DIRECTORY>(instance + exportVA);
+			const DWORD* functionNames = reinterpret_cast<DWORD*>(instance + exportDirectory->AddressOfNames);
+			for (DWORD i = 0; i < exportDirectory->NumberOfNames; i++)
+			{
+				const char* nameRva = reinterpret_cast<const char*>(instance + functionNames[i]);
+				auto it = std::find(exportsToCheck.begin(), exportsToCheck.end(), nameRva);
+				if (it != exportsToCheck.end())
+				{
+					exportsToCheck.erase(it);
+					if (exportsToCheck.empty())
+					{
+						// Early out if all required functions are found
+						break;
+					}
+				}
+			}
+		}
+		FreeLibrary(file);
+	}
+	return exportsToCheck.empty();
+}

source/exportChecker.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <initializer_list>
+#include <string_view>
+
+bool CheckExports(const wchar_t* path, std::initializer_list<std::string_view> exports);