Clean up input hook code

This cleans up the input hooking code with better comments, use of
nullptr instead of 0, and more accurate error handling.

The "more accurate error handling" is that previously if one hook was
registered and the other one was not then the message pump would not
be run, which could cause issues.

Author: randomascii

UIforETW/KeyLoggerThread.cpp

@@ -165,7 +165,7 @@ LRESULT CALLBACK LowLevelKeyboardHook(int nCode, WPARAM wParam, LPARAM lParam)
 		ETWKeyDown(code, keyDownDetails.c_str(), 0, 0);
 	}
 
-	return CallNextHookEx(0, nCode, wParam, lParam);
+	return CallNextHookEx(nullptr, nCode, wParam, lParam);
 }
 
 _Pre_satisfies_(nCode == HC_ACTION)
@@ -228,7 +228,7 @@ LRESULT CALLBACK LowLevelMouseHook(int nCode, WPARAM wParam, LPARAM lParam) noex
 		}
 	}
 
-	return CallNextHookEx(0, nCode, wParam, lParam);
+	return CallNextHookEx(nullptr, nCode, wParam, lParam);
 }
 
 
@@ -252,30 +252,43 @@ DWORD __stdcall InputThread(LPVOID) noexcept
 	// processed in a timely manner or else bad things will happen. Doing this on a
 	// separate thread is a good idea, but even then bad things will happen to your system
 	// if you halt in a debugger. Even simple things like calling printf() from the hook
-	// can easily cause system deadlocks which render the mouse unable to move!
-	HHOOK keyHook = SetWindowsHookEx(WH_KEYBOARD_LL, LowLevelKeyboardHook, NULL, 0);
-	HHOOK mouseHook = SetWindowsHookEx(WH_MOUSE_LL, LowLevelMouseHook, NULL, 0);
-
-	if (!keyHook && !mouseHook)
-		return 0;
-
-	// Run a message pump -- necessary so that the hooks will be processed
-	BOOL bRet;
-	MSG msg;
-	// Keeping pumping messages until WM_QUIT is received. If this is opened
-	// in a child thread then you can terminate it by using PostThreadMessage
-	// to send WM_QUIT.
-	while ((bRet = GetMessage(&msg, NULL, 0, 0)) != 0)
+	// can easily cause system deadlocks which cause all input to be processed
+	// very slowly.
+	// The default OS hook timeout seems to be 300 ms, which is long enough to
+	// make input delays noticeable, but short enough to make the system sort of
+	// usable. You can set a shorter timeout (10 ms in this case) with this
+	// command:
+	// reg add "HKCU\Control Panel\Desktop" /v LowLevelHooksTimeout /t REG_DWORD /f /d 10
+	// Occasional input delays were, in one case, tracked down to an input hook
+	// (unknown owner) that was briefly timing out. Twitter discussion is here:
+	// https://twitter.com/BruceDawson0xB/status/1673375468127670273
+	HHOOK keyHook = SetWindowsHookEx(WH_KEYBOARD_LL, LowLevelKeyboardHook, nullptr, 0);
+	HHOOK mouseHook = SetWindowsHookEx(WH_MOUSE_LL, LowLevelMouseHook, nullptr, 0);
+
+	// Run the message pump if either hook is successfully registered (they should
+	// always both be registered).
+	if (keyHook || mouseHook)
 	{
-		if (bRet == -1)
-		{
-			// handle the error and possibly exit
-			break;
-		}
-		else
+		// Run a message pump -- necessary so that the hooks will be processed
+		BOOL bRet;
+		MSG msg;
+		// Keeping pumping messages until WM_QUIT is received. If this is running
+		// in a child thread then you can terminate it by using PostThreadMessage
+		// to send WM_QUIT.
+		while ((bRet = GetMessageW(&msg, nullptr, 0, 0)) != 0)
 		{
-			TranslateMessage(&msg);
-			DispatchMessage(&msg);
+			// GetMessageW will normally only return when WM_QUIT is received, so this
+			// loop normally doesn't ever run.
+			if (bRet == -1)
+			{
+				// Unexpected error. Quit.
+				break;
+			}
+			else
+			{
+				TranslateMessage(&msg);
+				DispatchMessage(&msg);
+			}
 		}
 	}
 
@@ -312,7 +325,7 @@ void SetKeyloggingState(enum KeyLoggerState state) noexcept
 	// it isn't running.
 	if (!s_hThread)
 	{
-		s_hThread = CreateThread(NULL, 0, InputThread, NULL, 0, &s_threadID);
+		s_hThread = CreateThread(nullptr, 0, InputThread, nullptr, 0, &s_threadID);
 	}
 
 	switch (state)