Main.cpp

// Main.cpp
// UniversalPauseButton
// Ryan Ries, 2015
// ryan@myotherpcisacloud.com
// https://github.com/ryanries/UniversalPauseButton/
// Must compile in Unicode.

#include <Windows.h>
#include <Psapi.h>
#include <stdio.h>
#include "resource.h"

#define WM_TRAYICON (WM_USER + 1)

// WARNING: Undocumented Win32 API functions!
// Microsoft may change these at any time; they are not guaranteed to work on the next version of Windows.
typedef LONG(NTAPI* _NtSuspendProcess) (IN HANDLE ProcessHandle);
typedef LONG(NTAPI* _NtResumeProcess) (IN HANDLE ProcessHandle);
typedef HWND(NTAPI* _HungWindowFromGhostWindow) (IN HWND GhostWindowHandle);

_NtSuspendProcess NtSuspendProcess = (_NtSuspendProcess)GetProcAddress(GetModuleHandle(L"ntdll.dll"), "NtSuspendProcess");
_NtResumeProcess NtResumeProcess = (_NtResumeProcess)GetProcAddress(GetModuleHandle(L"ntdll.dll"), "NtResumeProcess");
_HungWindowFromGhostWindow HungWindowFromGhostWindow = (_HungWindowFromGhostWindow)GetProcAddress(GetModuleHandle(L"user32.dll"), "HungWindowFromGhostWindow");

NOTIFYICONDATA G_TrayNotifyIconData;
HANDLE G_Mutex;

// NOTE(Ryan): This function returns true if the string ends with the specified Suffix/substring.
// Uses wide characters. Not case sensitive.
int StringEndsWith_WI(_In_ const wchar_t *String, _In_ const wchar_t *Ending)
{
	if (String == NULL || Ending == NULL)
	{
		return(0);
	}

	size_t StringLength = wcslen(String);
	size_t EndingLength = wcslen(Ending);

	if (EndingLength > StringLength)
	{
		return(0);
	}
	
	return(0 == _wcsnicmp(String + StringLength - EndingLength, Ending, EndingLength));
}

// NOTE(Ryan): This function returns true if the string starts with the specified prefix/substring.
// ASCII characters. Not case sensitive.
int StringStartsWith_AI(_In_ const char* String, _In_ const char* Beginning)
{
	if (String == NULL || Beginning == NULL)
	{
		return(0);
	}

	size_t PrefixLength = strlen(Beginning);
	size_t StringLength = strlen(String);

	return(StringLength < PrefixLength ? FALSE : _strnicmp(String, Beginning, PrefixLength) == 0);
}


// The WindowProc (callback) for WinMain's WindowClass.
// Basically the system tray does nothing except lets the user know that it's running.
// If the user clicks the tray icon in any way it will ask if they want to exit the app.
LRESULT CALLBACK WindowClassCallback(_In_ HWND Window, _In_ UINT Message, _In_ WPARAM WParam, _In_ LPARAM LParam)
{
	LRESULT Result = 0;
	static BOOL QuitMessageBoxIsShowing = FALSE;

	switch (Message)
	{
		case WM_TRAYICON:
		{
			if (!QuitMessageBoxIsShowing && (LParam == WM_LBUTTONDOWN || LParam == WM_RBUTTONDOWN || LParam == WM_MBUTTONDOWN))
			{
				QuitMessageBoxIsShowing = TRUE;
				if (MessageBox(Window, L"Quit UniversalPauseButton?", L"Are you sure?", MB_YESNO | MB_ICONQUESTION | MB_SYSTEMMODAL) == IDYES)
				{
					Shell_NotifyIcon(NIM_DELETE, &G_TrayNotifyIconData);
					PostQuitMessage(0);
				}
				else
				{
					QuitMessageBoxIsShowing = FALSE;
				}
			}
			break;
		}
		default:
		{
			Result = DefWindowProc(Window, Message, WParam, LParam);
			break;
		}
	}
	return(Result);
}

// Returns 0x13 (VK_PAUSE) upon any failure. Therefore, the Pause/Break key is the default.
// The first line of the file must begin with KEY=...
int LoadPauseKeyFromSettingsFile(_In_ wchar_t* Filename)
{
	HANDLE FileHandle = CreateFile(Filename, GENERIC_READ, FILE_SHARE_READ,	NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL,	NULL);

	if (FileHandle == INVALID_HANDLE_VALUE)
	{
		goto Default;
	}
	
	char  KeyLine[32] = { 0 };
	char  Buffer[2]   = { 0 };
	DWORD ByteRead    = 0;

	do
	{
		if (!ReadFile(FileHandle, Buffer, 1, &ByteRead, NULL))
		{
			goto Default;
		}

		if (Buffer[0] == '\r' || Buffer[0] == '\n')
		{
			break;
		}

		size_t Length = strlen(KeyLine);
		if (Length > 30)
		{
			goto Default;
		}

		KeyLine[Length] = Buffer[0];		
		memset(Buffer, 0, sizeof(Buffer));
	} while (ByteRead == 1);

	if (!StringStartsWith_AI(KeyLine, "KEY="))
	{
		goto Default;
	}

	char KeyNumberAsString[16] = { 0 };

	for (DWORD Counter = 4; Counter < strlen(KeyLine); Counter++)
	{
		KeyNumberAsString[Counter - 4] = KeyLine[Counter];
	}

	long StringToNumber = strtol(KeyNumberAsString, NULL, 16);
	if (StringToNumber < 0x01 || StringToNumber > 0xFF)
	{
		goto Default;
	}

	if (FileHandle != INVALID_HANDLE_VALUE && FileHandle != NULL)
	{
		CloseHandle(FileHandle);
	}
	return(StringToNumber);	

Default:
	if (FileHandle != INVALID_HANDLE_VALUE && FileHandle != NULL)
	{
		CloseHandle(FileHandle);		
	}
	return(0x13);	
}

// Entry point.
int CALLBACK WinMain(_In_ HINSTANCE Instance, _In_opt_ HINSTANCE, _In_ LPSTR, _In_ int)
{
	G_Mutex = CreateMutex(NULL, FALSE, L"UniversalPauseButton");
	if (GetLastError() == ERROR_ALREADY_EXISTS)
	{
		MessageBox(NULL, L"An instance of the program is already running.", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(ERROR_ALREADY_EXISTS);
	}

	if (NtSuspendProcess == NULL || NtResumeProcess == NULL)
	{
		MessageBox(NULL, L"Unable to locate ntdll.dll functions!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	if (HungWindowFromGhostWindow == NULL)
	{
		MessageBox(NULL, L"Unable to load HungWindowFromGhostWindow from user32.dll!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	WNDCLASS SysTrayWindowClass = { 0 };

	SysTrayWindowClass.style         = CS_HREDRAW | CS_VREDRAW;
	SysTrayWindowClass.hInstance     = Instance;
	SysTrayWindowClass.lpszClassName = L"UniversalPauseButton_Systray_WindowClass";
	SysTrayWindowClass.hbrBackground = CreateSolidBrush(RGB(255, 0, 255));
	SysTrayWindowClass.lpfnWndProc   = WindowClassCallback;

	if (RegisterClass(&SysTrayWindowClass) == 0)
	{
		MessageBox(NULL, L"Failed to register WindowClass!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	HWND SystrayWindow = CreateWindowEx(
		WS_EX_TOOLWINDOW,
		SysTrayWindowClass.lpszClassName,
		L"UniversalPauseButton_Systray_Window",
		WS_ICONIC,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		0,
		0,
		Instance,
		0);

	if (SystrayWindow == 0)
	{
		MessageBox(NULL, L"Failed to create SystrayWindow!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	G_TrayNotifyIconData.cbSize           = sizeof(NOTIFYICONDATA);
	G_TrayNotifyIconData.hWnd             = SystrayWindow;
	G_TrayNotifyIconData.uID              = 1982;
	G_TrayNotifyIconData.uFlags           = NIF_ICON | NIF_MESSAGE | NIF_TIP;
	G_TrayNotifyIconData.uCallbackMessage = WM_TRAYICON;

	wcscpy_s(G_TrayNotifyIconData.szTip, L"Universal Pause Button v1.0.3");

	G_TrayNotifyIconData.hIcon = (HICON)LoadImage(GetModuleHandle(NULL), MAKEINTRESOURCE(IDI_ICON1), IMAGE_ICON, 0, 0, NULL);

	if (G_TrayNotifyIconData.hIcon == NULL)
	{
		MessageBox(NULL, L"Failed to load systray icon resource!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	if (Shell_NotifyIcon(NIM_ADD, &G_TrayNotifyIconData) == FALSE)
	{
		MessageBox(NULL, L"Failed to register systray icon!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
		return(E_FAIL);
	}

	int PauseKey = LoadPauseKeyFromSettingsFile(L"settings.txt");

	MSG        SysTrayWindowMessage                 = { 0 };
	DWORD      PreviouslySuspendedProcessID			= 0;
	HWND	   PreviouslySuspendedWnd				= 0;
	wchar_t    PreviouslySuspendedProcessText[256]  = { 0 };
	HANDLE     ProcessHandle                        = 0;
	static int PauseKeyWasDown                      = 0;

	while (SysTrayWindowMessage.message != WM_QUIT)
	{
		while (PeekMessage(&SysTrayWindowMessage, SystrayWindow, 0, 0, PM_REMOVE))
		{
			DispatchMessage(&SysTrayWindowMessage);
		}

		int PauseKeyIsDown = GetAsyncKeyState(PauseKey);

		if (PauseKeyIsDown && !PauseKeyWasDown)
		{
			HWND ForegroundWindow = GetForegroundWindow();

			// Check if the focused window is in a non-responsive state.
			if (IsHungAppWindow(ForegroundWindow)) 
			{
				// If the foreground window is non-responsive the current value of ForegroundWindow will differ
				// from the actual application window handle (used when the process was first suspended).
				// In this case we should check if the non-responsive foreground window is associated with a
				// previously suspended process.
				// This is done by checking if the ghost window (created by windows dwm.exe) returns the correct handle to the original window.
				HWND nonResponsiveWnd = HungWindowFromGhostWindow(ForegroundWindow);
				if (nonResponsiveWnd == PreviouslySuspendedWnd) 
				{
					ForegroundWindow = PreviouslySuspendedWnd;
				}
			}

			if (!ForegroundWindow)
			{
				MessageBox(NULL, L"Unable to detect foreground window!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
				goto EndOfLoop;
			}

			DWORD ProcessID = 0;
			GetWindowThreadProcessId(ForegroundWindow, &ProcessID);
			if (ProcessID == 0)
			{
				MessageBox(NULL, L"Unable to get process ID of foreground window!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
				goto EndOfLoop;
			}
			
			ProcessHandle = OpenProcess(PROCESS_ALL_ACCESS, FALSE, ProcessID);
			if (ProcessHandle == 0)
			{
				MessageBox(NULL, L"OpenProcess failed!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
				goto EndOfLoop;
			}

			if (PreviouslySuspendedProcessID == 0)
			{
				// I won't let you pause your shell. Nothing good will come of that.
				// Later I will get the user's shell from the registry, just to cover the 0.001% case
				// that the user has a custom shell.
				wchar_t ImageFileName[MAX_PATH] = { 0 };
				GetProcessImageFileName(ProcessHandle, ImageFileName, sizeof(ImageFileName) / sizeof(wchar_t));
				if (!StringEndsWith_WI(ImageFileName, L"explorer.exe"))
				{
					NtSuspendProcess(ProcessHandle);
					PreviouslySuspendedProcessID = ProcessID;
					PreviouslySuspendedWnd = ForegroundWindow;
					GetWindowText(ForegroundWindow, PreviouslySuspendedProcessText, sizeof(PreviouslySuspendedProcessText) / sizeof(wchar_t));
				}
				else
				{
					MessageBox(NULL, L"You cannot pause your shell.", L"UniversalPauseButton Error", MB_OK | MB_ICONWARNING | MB_SYSTEMMODAL);
				}
			}
			else if (PreviouslySuspendedProcessID == ProcessID)
			{
				NtResumeProcess(ProcessHandle);
				PreviouslySuspendedProcessID = 0;
				PreviouslySuspendedWnd = 0;
				memset(PreviouslySuspendedProcessText, 0, sizeof(PreviouslySuspendedProcessText));
			}
			else
			{
				// The user pressed the pause button while focused on another process than what was
				// originally paused and the first process is still paused.
				DWORD AllProcesses[2048] = { 0 };
				DWORD BytesReturned = 0;
				BOOL PreviouslySuspendedProcessIsStillRunning = FALSE;

				if (EnumProcesses(AllProcesses, sizeof(AllProcesses), &BytesReturned) != 0)
				{
					for (DWORD Counter = 0; Counter < (BytesReturned / sizeof(DWORD)); Counter++)
					{
						if ((AllProcesses[Counter] != 0) && AllProcesses[Counter] == PreviouslySuspendedProcessID)
						{
							PreviouslySuspendedProcessIsStillRunning = TRUE;										
						}
					}
					if (PreviouslySuspendedProcessIsStillRunning)
					{
						wchar_t MessageBoxBuffer[1024] = { 0 };
						_snwprintf_s(MessageBoxBuffer, sizeof(MessageBoxBuffer), L"You must first unpause %s (PID %d) before pausing another program.", PreviouslySuspendedProcessText, PreviouslySuspendedProcessID);
						MessageBox(ForegroundWindow, MessageBoxBuffer, L"Universal Pause Button", MB_OK | MB_ICONINFORMATION | MB_SYSTEMMODAL);
					}
					else
					{
						// The paused process is no more, so reset.
						PreviouslySuspendedProcessID = 0;
						PreviouslySuspendedWnd = 0;
						memset(PreviouslySuspendedProcessText, 0, sizeof(PreviouslySuspendedProcessText));
					}
				}
				else
				{
					MessageBox(NULL, L"EnumProcesses failed!", L"UniversalPauseButton Error", MB_OK | MB_ICONERROR);
				}
			}
		}
		
		// http://stackoverflow.com/questions/245742/examples-of-good-gotos-in-c-or-c
	
	EndOfLoop:
		if (ProcessHandle != INVALID_HANDLE_VALUE && ProcessHandle != NULL)
		{
			__try
			{
				CloseHandle(ProcessHandle);
				ProcessHandle = NULL;
			}
			__except (EXCEPTION_EXECUTE_HANDLER)
			{
				// Please help me stop from throwing this exception. I hate exceptions.				
			}
		}
		
		PauseKeyWasDown = PauseKeyIsDown;
		Sleep(10);
	}

	return(S_OK);
}