Phase 1a: input forwarding via DLL injection + XInput hook

The host can now inject coop_hook.dll into a running game and forward
controller state to it over shared memory, so the game reads the host's
(eventually the guest's) input and nothing else.

- hook/: coop_hook.dll. DllMain spawns a worker that opens the shared-memory
  channel (named by the game's pid) and installs SafetyHook inline hooks on
  XInputGetState/GetStateEx/GetCapabilities/SetState. Detours synthesize state
  from shared memory; unmanaged slots report disconnected, hiding physical pads.
- host/: process picker (Toolhelp32), CreateRemoteThread(LoadLibraryW) injector
  with an IsWow64Process2 bitness guard, IPC server publishing pads each frame,
  and an ImGui Injection panel wiring it together.
- tests/: hook_selftest exercises the IPC seqlock + hook detours in-process
  (no game/controller needed); passes.

Build: SafetyHook wired in (COOP_BUILD_HOOK=ON), Zydis via FetchContent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/CMakeLists.txt

@@ -3,7 +3,11 @@ add_executable(coop_host WIN32
 	src/d3d11_window.cpp
 	src/imgui_layer.cpp
 	src/debug_overlay.cpp
-	src/input/xinput_source.cpp)
+	src/injection_panel.cpp
+	src/input/xinput_source.cpp
+	src/inject/process_list.cpp
+	src/inject/injector.cpp
+	src/ipc/ipc_server.cpp)
 
 target_include_directories(coop_host PRIVATE src)
 

host/src/inject/injector.cpp

@@ -0,0 +1,130 @@
+#include "inject/injector.hpp"
+
+#include <windows.h>
+
+namespace coop
+{
+
+const char* to_string(InjectStatus status)
+{
+	switch (status)
+	{
+	case InjectStatus::Ok:
+		return "OK";
+	case InjectStatus::OpenProcessFailed:
+		return "OpenProcess failed (try running as administrator)";
+	case InjectStatus::BitnessMismatch:
+		return "target is 32-bit; x86 hook not built yet";
+	case InjectStatus::DllNotFound:
+		return "coop_hook.dll not found next to the host";
+	case InjectStatus::AllocFailed:
+		return "VirtualAllocEx failed";
+	case InjectStatus::WriteFailed:
+		return "WriteProcessMemory failed";
+	case InjectStatus::RemoteThreadFailed:
+		return "CreateRemoteThread failed";
+	case InjectStatus::RemoteLoadFailed:
+		return "LoadLibraryW returned null in the target";
+	}
+	return "unknown";
+}
+
+namespace
+{
+
+InjectResult fail(InjectStatus status)
+{
+	return InjectResult{status, GetLastError()};
+}
+
+// Returns true if `process` runs as a 32-bit (WOW64) process on this 64-bit host.
+bool is_wow64_process(HANDLE process)
+{
+	USHORT process_machine = IMAGE_FILE_MACHINE_UNKNOWN;
+	USHORT native_machine = IMAGE_FILE_MACHINE_UNKNOWN;
+	if (IsWow64Process2(process, &process_machine, &native_machine))
+	{
+		return process_machine != IMAGE_FILE_MACHINE_UNKNOWN;
+	}
+	return false; // be permissive if the query is unavailable
+}
+
+} // namespace
+
+InjectResult inject_dll(unsigned long pid, const std::wstring& dll_path)
+{
+	if (GetFileAttributesW(dll_path.c_str()) == INVALID_FILE_ATTRIBUTES)
+	{
+		return fail(InjectStatus::DllNotFound);
+	}
+
+	const DWORD access = PROCESS_CREATE_THREAD | PROCESS_QUERY_INFORMATION | PROCESS_VM_OPERATION |
+	                     PROCESS_VM_WRITE | PROCESS_VM_READ;
+	HANDLE process = OpenProcess(access, FALSE, pid);
+	if (process == nullptr)
+	{
+		return fail(InjectStatus::OpenProcessFailed);
+	}
+
+	struct HandleGuard
+	{
+		HANDLE h;
+		~HandleGuard()
+		{
+			if (h != nullptr)
+			{
+				CloseHandle(h);
+			}
+		}
+	} process_guard{process};
+
+	if (is_wow64_process(process))
+	{
+		return InjectResult{InjectStatus::BitnessMismatch, 0};
+	}
+
+	const SIZE_T bytes = (dll_path.size() + 1) * sizeof(wchar_t);
+	void* remote = VirtualAllocEx(process, nullptr, bytes, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
+	if (remote == nullptr)
+	{
+		return fail(InjectStatus::AllocFailed);
+	}
+
+	InjectResult result{InjectStatus::Ok, 0};
+
+	if (!WriteProcessMemory(process, remote, dll_path.c_str(), bytes, nullptr))
+	{
+		result = fail(InjectStatus::WriteFailed);
+	}
+	else
+	{
+		// kernel32 is mapped at the same address in every process, so LoadLibraryW's
+		// address in this process is valid as the remote thread's start routine.
+		auto load_library =
+		    reinterpret_cast<LPTHREAD_START_ROUTINE>(GetProcAddress(GetModuleHandleW(L"kernel32.dll"), "LoadLibraryW"));
+		HANDLE thread = CreateRemoteThread(process, nullptr, 0, load_library, remote, 0, nullptr);
+		if (thread == nullptr)
+		{
+			result = fail(InjectStatus::RemoteThreadFailed);
+		}
+		else
+		{
+			WaitForSingleObject(thread, INFINITE);
+			DWORD exit_code = 0;
+			GetExitCodeThread(thread, &exit_code);
+			CloseHandle(thread);
+			// LoadLibraryW returns the module handle; 0 means it failed to load.
+			// (The handle is truncated to 32 bits here, but zero vs non-zero is
+			// all we need to distinguish success from failure.)
+			if (exit_code == 0)
+			{
+				result = InjectResult{InjectStatus::RemoteLoadFailed, 0};
+			}
+		}
+	}
+
+	VirtualFreeEx(process, remote, 0, MEM_RELEASE);
+	return result;
+}
+
+} // namespace coop

host/src/inject/injector.hpp

@@ -0,0 +1,34 @@
+// Loads coop_hook.dll into a target process via the classic
+// CreateRemoteThread(LoadLibraryW) technique.
+#pragma once
+
+#include <string>
+
+namespace coop
+{
+
+enum class InjectStatus
+{
+	Ok,
+	OpenProcessFailed, // insufficient rights (try running the host as admin)
+	BitnessMismatch,   // 32-bit target; needs the x86 hook (later phase)
+	DllNotFound,
+	AllocFailed,
+	WriteFailed,
+	RemoteThreadFailed,
+	RemoteLoadFailed, // LoadLibraryW returned null inside the target
+};
+
+struct InjectResult
+{
+	InjectStatus status = InjectStatus::OpenProcessFailed;
+	unsigned long os_error = 0; // GetLastError at the point of failure, if any
+};
+
+const char* to_string(InjectStatus status);
+
+// Injects `dll_path` (absolute) into the process with `pid`. The host and DLL
+// must match the target's bitness; 32-bit targets are rejected up front.
+InjectResult inject_dll(unsigned long pid, const std::wstring& dll_path);
+
+} // namespace coop

host/src/inject/process_list.cpp

@@ -0,0 +1,43 @@
+#include "inject/process_list.hpp"
+
+#include <algorithm>
+
+#include <windows.h>
+#include <tlhelp32.h>
+
+namespace coop
+{
+
+std::vector<ProcessEntry> list_processes()
+{
+	std::vector<ProcessEntry> result;
+
+	HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+	if (snapshot == INVALID_HANDLE_VALUE)
+	{
+		return result;
+	}
+
+	PROCESSENTRY32W entry = {};
+	entry.dwSize = sizeof(entry);
+	if (Process32FirstW(snapshot, &entry))
+	{
+		do
+		{
+			if (entry.th32ProcessID == 0)
+			{
+				continue;
+			}
+			result.push_back(ProcessEntry{entry.th32ProcessID, entry.szExeFile});
+		} while (Process32NextW(snapshot, &entry));
+	}
+	CloseHandle(snapshot);
+
+	std::sort(result.begin(), result.end(), [](const ProcessEntry& a, const ProcessEntry& b) {
+		const int cmp = _wcsicmp(a.exe_name.c_str(), b.exe_name.c_str());
+		return cmp != 0 ? cmp < 0 : a.pid < b.pid;
+	});
+	return result;
+}
+
+} // namespace coop

host/src/inject/process_list.hpp

@@ -0,0 +1,20 @@
+// Enumerates running processes for the injection target picker.
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace coop
+{
+
+struct ProcessEntry
+{
+	unsigned long pid = 0;
+	std::wstring exe_name; // image base name, e.g. "game.exe"
+};
+
+// Snapshot of current processes, sorted by exe name (case-insensitive). System
+// idle/0 pids are skipped.
+std::vector<ProcessEntry> list_processes();
+
+} // namespace coop

host/src/injection_panel.cpp

@@ -0,0 +1,174 @@
+#include "injection_panel.hpp"
+
+#include <windows.h>
+
+#include "inject/injector.hpp"
+
+namespace coop
+{
+
+namespace
+{
+
+const ImVec4 kGreen(0.4f, 1.0f, 0.4f, 1.0f);
+const ImVec4 kRed(1.0f, 0.45f, 0.4f, 1.0f);
+const ImVec4 kGrey(0.7f, 0.7f, 0.7f, 1.0f);
+
+std::string narrow(const std::wstring& w)
+{
+	if (w.empty())
+	{
+		return {};
+	}
+	const int len = WideCharToMultiByte(CP_UTF8, 0, w.c_str(), static_cast<int>(w.size()), nullptr, 0, nullptr, nullptr);
+	std::string out(static_cast<std::size_t>(len), '\0');
+	WideCharToMultiByte(CP_UTF8, 0, w.c_str(), static_cast<int>(w.size()), out.data(), len, nullptr, nullptr);
+	return out;
+}
+
+bool contains_ci(const std::wstring& haystack, const char* needle_utf8)
+{
+	if (needle_utf8 == nullptr || needle_utf8[0] == '\0')
+	{
+		return true;
+	}
+	const std::string hay = narrow(haystack);
+	std::string h = hay, n = needle_utf8;
+	for (char& c : h)
+	{
+		c = static_cast<char>(::tolower(static_cast<unsigned char>(c)));
+	}
+	for (char& c : n)
+	{
+		c = static_cast<char>(::tolower(static_cast<unsigned char>(c)));
+	}
+	return h.find(n) != std::string::npos;
+}
+
+// Absolute path to coop_hook.dll, assumed to sit next to the host executable.
+std::wstring hook_dll_path()
+{
+	wchar_t buffer[MAX_PATH] = {};
+	const DWORD len = GetModuleFileNameW(nullptr, buffer, MAX_PATH);
+	std::wstring path(buffer, len);
+	const std::size_t slash = path.find_last_of(L"\\/");
+	if (slash != std::wstring::npos)
+	{
+		path.resize(slash + 1);
+	}
+	path += L"coop_hook.dll";
+	return path;
+}
+
+} // namespace
+
+InjectionPanel::InjectionPanel()
+{
+	refresh_processes();
+}
+
+void InjectionPanel::refresh_processes()
+{
+	processes_ = list_processes();
+}
+
+void InjectionPanel::inject_selected()
+{
+	if (selected_pid_ == 0)
+	{
+		status_ = "Select a target process first.";
+		status_color_ = kRed;
+		return;
+	}
+
+	// Bring up the shared-memory channel before injecting so the hook finds it
+	// immediately on load.
+	if (!server_.start(selected_pid_))
+	{
+		status_ = "Failed to create shared memory.";
+		status_color_ = kRed;
+		return;
+	}
+
+	const InjectResult result = inject_dll(selected_pid_, hook_dll_path());
+	if (result.status == InjectStatus::Ok)
+	{
+		status_ = "Injected into " + narrow(selected_name_) + " (pid " + std::to_string(selected_pid_) + ").";
+		status_color_ = kGreen;
+	}
+	else
+	{
+		server_.stop();
+		status_ = std::string("Injection failed: ") + to_string(result.status);
+		if (result.os_error != 0)
+		{
+			status_ += " [err " + std::to_string(result.os_error) + "]";
+		}
+		status_color_ = kRed;
+	}
+}
+
+void InjectionPanel::draw()
+{
+	ImGui::SetNextWindowPos(ImVec2(24, 360), ImGuiCond_FirstUseEver);
+	ImGui::SetNextWindowSize(ImVec2(420, 380), ImGuiCond_FirstUseEver);
+	ImGui::Begin("Injection");
+
+	if (server_.running())
+	{
+		ImGui::TextColored(kGreen, "Forwarding input to pid %lu", server_.target_pid());
+		if (ImGui::Button("Stop forwarding"))
+		{
+			server_.stop();
+			status_ = "Stopped.";
+			status_color_ = kGrey;
+		}
+		ImGui::Separator();
+	}
+
+	ImGui::TextUnformatted("Target process");
+	if (ImGui::Button("Refresh"))
+	{
+		refresh_processes();
+	}
+	ImGui::SameLine();
+	ImGui::SetNextItemWidth(-1.0f);
+	ImGui::InputTextWithHint("##filter", "filter by name...", filter_, sizeof(filter_));
+
+	if (ImGui::BeginListBox("##processes", ImVec2(-1.0f, 200.0f)))
+	{
+		for (const ProcessEntry& entry : processes_)
+		{
+			if (!contains_ci(entry.exe_name, filter_))
+			{
+				continue;
+			}
+			const bool selected = entry.pid == selected_pid_;
+			char label[300];
+			snprintf(label, sizeof(label), "%-40s  %lu", narrow(entry.exe_name).c_str(), entry.pid);
+			if (ImGui::Selectable(label, selected))
+			{
+				selected_pid_ = entry.pid;
+				selected_name_ = entry.exe_name;
+			}
+		}
+		ImGui::EndListBox();
+	}
+
+	const bool can_inject = selected_pid_ != 0;
+	ImGui::BeginDisabled(!can_inject);
+	if (ImGui::Button("Inject & Connect", ImVec2(-1.0f, 0.0f)))
+	{
+		inject_selected();
+	}
+	ImGui::EndDisabled();
+
+	if (!status_.empty())
+	{
+		ImGui::TextColored(status_color_, "%s", status_.c_str());
+	}
+
+	ImGui::End();
+}
+
+} // namespace coop

host/src/injection_panel.hpp

@@ -0,0 +1,44 @@
+// ImGui panel that drives the input-forwarding pipeline: pick a target process,
+// inject coop_hook.dll, and stream pad state to it over shared memory.
+#pragma once
+
+#include <array>
+#include <string>
+#include <vector>
+
+#include "coop/protocol.hpp"
+#include "imgui.h"
+#include "inject/process_list.hpp"
+#include "ipc/ipc_server.hpp"
+
+namespace coop
+{
+
+class InjectionPanel
+{
+public:
+	InjectionPanel();
+
+	void draw();
+
+	// Forward the latest pad snapshot to the injected hook (if connected).
+	void publish(const std::array<PadInfo, kMaxPads>& pads)
+	{
+		server_.publish(pads);
+	}
+
+private:
+	void refresh_processes();
+	void inject_selected();
+
+	std::vector<ProcessEntry> processes_;
+	char filter_[128] = {};
+	unsigned long selected_pid_ = 0;
+	std::wstring selected_name_;
+
+	IpcServer server_;
+	std::string status_;
+	ImVec4 status_color_;
+};
+
+} // namespace coop

host/src/ipc/ipc_server.cpp

@@ -0,0 +1,54 @@
+#include "ipc/ipc_server.hpp"
+
+namespace coop
+{
+
+bool IpcServer::start(unsigned long target_pid)
+{
+	stop();
+
+	if (!shm_.create(shared_memory_name(target_pid), sizeof(SharedBlock)))
+	{
+		return false;
+	}
+
+	auto* block = shm_.as<SharedBlock>();
+	// Fresh CreateFileMapping pages are zero-filled; set the header before the
+	// hook (which validates magic/version) has a chance to read it.
+	block->version = kProtocolVersion;
+	block->pad_count = 0;
+	block->sequence.store(0, std::memory_order_relaxed);
+	block->magic = kProtocolMagic; // publish magic last so a racing reader bails
+
+	block_ = block;
+	target_pid_ = target_pid;
+	return true;
+}
+
+void IpcServer::publish(const std::array<PadInfo, kMaxPads>& pads)
+{
+	if (block_ == nullptr)
+	{
+		return;
+	}
+	CoopPadState states[kMaxPads];
+	for (std::size_t i = 0; i < pads.size(); ++i)
+	{
+		states[i] = pads[i].state;
+		states[i].connected = pads[i].connected ? 1 : 0;
+	}
+	publish_pads(*block_, states, kMaxPads);
+}
+
+void IpcServer::stop()
+{
+	if (block_ != nullptr)
+	{
+		block_->magic = 0; // invalidate so a late hook read won't trust stale data
+		block_ = nullptr;
+	}
+	shm_.reset();
+	target_pid_ = 0;
+}
+
+} // namespace coop

host/src/ipc/ipc_server.hpp

@@ -0,0 +1,41 @@
+// Host side of the IPC channel: creates the shared-memory section (named by the
+// target game's pid) and publishes the forwarded controller state each frame.
+#pragma once
+
+#include <array>
+
+#include "coop/protocol.hpp"
+#include "coop/shared_memory.hpp"
+#include "input/input_source.hpp"
+
+namespace coop
+{
+
+class IpcServer
+{
+public:
+	// Creates and initializes the section for `target_pid`. The injected hook
+	// derives the same name from its own pid and opens it.
+	bool start(unsigned long target_pid);
+
+	// Pushes the current pad snapshot to the hook. No-op if not started.
+	void publish(const std::array<PadInfo, kMaxPads>& pads);
+
+	void stop();
+
+	[[nodiscard]] bool running() const
+	{
+		return block_ != nullptr;
+	}
+	[[nodiscard]] unsigned long target_pid() const
+	{
+		return target_pid_;
+	}
+
+private:
+	SharedMemory shm_;
+	SharedBlock* block_ = nullptr;
+	unsigned long target_pid_ = 0;
+};
+
+} // namespace coop

host/src/main.cpp

@@ -14,6 +14,7 @@
 #include "d3d11_window.hpp"
 #include "debug_overlay.hpp"
 #include "imgui_layer.hpp"
+#include "injection_panel.hpp"
 #include "input/xinput_source.hpp"
 
 namespace
@@ -36,13 +37,16 @@ int run()
 	}
 
 	auto input = std::make_unique<coop::XInputSource>();
+	coop::InjectionPanel injection;
 
 	while (window.pump_messages())
 	{
 		input->poll();
+		injection.publish(input->pads());
 
 		imgui.begin_frame();
 		coop::draw_debug_overlay(*input);
+		injection.draw();
 
 		window.render_frame([&imgui]() { imgui.end_frame(); });
 	}