CoopAllTheThings/common/include/coop/shared_memory.hpp

// Thin RAII wrapper over a Win32 file-mapping section used as the host<->hook
// IPC transport. Header-only so both modules share one implementation.
#pragma once

#include <string>
#include <utility>

#include <windows.h>

#include "coop/protocol.hpp"

namespace coop
{

class SharedMemory
{
public:
	SharedMemory() = default;

	SharedMemory(const SharedMemory&) = delete;
	SharedMemory& operator=(const SharedMemory&) = delete;

	SharedMemory(SharedMemory&& other) noexcept
	{
		*this = std::move(other);
	}

	SharedMemory& operator=(SharedMemory&& other) noexcept
	{
		if (this != &other)
		{
			reset();
			mapping_ = std::exchange(other.mapping_, nullptr);
			view_ = std::exchange(other.view_, nullptr);
			size_ = std::exchange(other.size_, 0);
		}
		return *this;
	}

	~SharedMemory()
	{
		reset();
	}

	// Host side: create (or open if it already exists) the named section.
	bool create(const std::wstring& name, std::size_t size)
	{
		reset();
		mapping_ = CreateFileMappingW(INVALID_HANDLE_VALUE, nullptr, PAGE_READWRITE, 0,
		                              static_cast<DWORD>(size), name.c_str());
		if (mapping_ == nullptr)
		{
			return false;
		}
		return map(size);
	}

	// Hook side: open an existing section created by the host.
	bool open(const std::wstring& name, std::size_t size)
	{
		reset();
		mapping_ = OpenFileMappingW(FILE_MAP_ALL_ACCESS, FALSE, name.c_str());
		if (mapping_ == nullptr)
		{
			return false;
		}
		return map(size);
	}

	void reset()
	{
		if (view_ != nullptr)
		{
			UnmapViewOfFile(view_);
			view_ = nullptr;
		}
		if (mapping_ != nullptr)
		{
			CloseHandle(mapping_);
			mapping_ = nullptr;
		}
		size_ = 0;
	}

	[[nodiscard]] bool valid() const
	{
		return view_ != nullptr;
	}

	template <typename T>
	[[nodiscard]] T* as() const
	{
		return static_cast<T*>(view_);
	}

	[[nodiscard]] void* data() const
	{
		return view_;
	}

	[[nodiscard]] std::size_t size() const
	{
		return size_;
	}

private:
	bool map(std::size_t size)
	{
		view_ = MapViewOfFile(mapping_, FILE_MAP_ALL_ACCESS, 0, 0, size);
		if (view_ == nullptr)
		{
			CloseHandle(mapping_);
			mapping_ = nullptr;
			return false;
		}
		size_ = size;
		return true;
	}

	HANDLE mapping_ = nullptr;
	void* view_ = nullptr;
	std::size_t size_ = 0;
};

// Build the per-pid section name both sides agree on.
inline std::wstring shared_memory_name(unsigned long target_pid)
{
	return std::wstring(kSharedMemoryPrefix) + std::to_wstring(target_pid);
}

} // namespace coop