Working fix for #4055 (client shift key problem) in place

src/lib/synwinhk/synwinhk.cpp

@@ -118,6 +118,7 @@ static WPARAM			g_deadVirtKey     = 0;
 static WPARAM			g_deadRelease     = 0;
 static LPARAM			g_deadLParam      = 0;
 static BYTE				g_deadKeyState[256] = { 0 };
+static BYTE				g_keyState[256] = { 0 };
 static DWORD			g_hookThread      = 0;
 static DWORD			g_attachedThread  = 0;
 static bool				g_fakeInput       = false;
@@ -166,6 +167,7 @@ attachThreadToForeground()
             return false;
 
 		DWORD threadID = GetWindowThreadProcessId(window, NULL);
+
 		// skip if no change
 		if (g_attachedThread != threadID) {
 			// detach from previous thread
@@ -192,17 +194,37 @@ makeKeyMsg(UINT virtKey, char c, bool noAltGr)
 
 static
 void
-keyboardGetState(BYTE keys[256])
+keyboardGetState(BYTE keys[256], DWORD vkCode, bool kf_up)
 {
-	// we have to use GetAsyncKeyState() rather than GetKeyState() because
+	if (vkCode < 0 || vkCode >= 256) {
-	// we don't pass through most keys so the event synchronous state
+		return;
-	// doesn't get updated.  we do that because certain modifier keys have
-	// side effects, like alt and the windows key.
-	SHORT key;
-	for (int i = 0; i < 256; ++i) {
-		key     = GetAsyncKeyState(i);
-		keys[i] = (BYTE)((key < 0) ? 0x80u : 0);
 	}
+
+	// Keep track of key state on our own in case GetAsyncKeyState() fails
+	g_keyState[vkCode] = kf_up ? 0 : 0x80;
+	g_keyState[VK_SHIFT] = g_keyState[VK_LSHIFT] | g_keyState[VK_RSHIFT];
+
+	SHORT key;
+	// Test whether GetAsyncKeyState() is being honest with us
+	key = GetAsyncKeyState(vkCode);
+
+	if (key & 0x80) {
+		// The only time we know for sure that GetAsyncKeyState() is working 
+		// is when it tells us that the current key is down.
+		// In this case, update g_keyState to reflect what GetAsyncKeyState()
+		// is telling us, just in case we have gotten out of sync
+
+		for (int i = 0; i < 256; ++i) {
+			key = GetAsyncKeyState(i);
+			g_keyState[i] = (BYTE)((key < 0) ? 0x80u : 0);
+		}
+	}
+
+	// copy g_keyState to keys
+	for (int i = 0; i < 256; ++i) {
+		keys[i] = g_keyState[i];
+	}
+
 	key = GetKeyState(VK_CAPITAL);
 	keys[VK_CAPITAL] = (BYTE)(((key < 0) ? 0x80 : 0) | (key & 1));
 }
@@ -211,6 +233,9 @@ static
 bool
 doKeyboardHookHandler(WPARAM wParam, LPARAM lParam)
 {
+	DWORD vkCode = wParam;
+	bool kf_up = (lParam & (KF_UP << 16)) != 0;
+
 	// check for special events indicating if we should start or stop
 	// passing events through and not report them to the server.  this
 	// is used to allow the server to synthesize events locally but
@@ -254,7 +279,7 @@ doKeyboardHookHandler(WPARAM wParam, LPARAM lParam)
 
 	// we need the keyboard state for ToAscii()
 	BYTE keys[256];
-	keyboardGetState(keys);
+	keyboardGetState(keys, vkCode, kf_up);
 
 	// ToAscii() maps ctrl+letter to the corresponding control code
 	// and ctrl+backspace to delete.  we don't want those translations
@@ -437,6 +462,7 @@ doKeyboardHookHandler(WPARAM wParam, LPARAM lParam)
 		PostThreadMessage(g_threadID, SYNERGY_MSG_KEY, charAndVirtKey, lParam);
 	}
 
+
 	if (g_mode == kHOOK_RELAY_EVENTS) {
 		// let certain keys pass through
 		switch (wParam) {
@@ -469,7 +495,7 @@ static
 bool
 keyboardHookHandler(WPARAM wParam, LPARAM lParam)
 {
-	attachThreadToForeground();
+	bool attached = attachThreadToForeground();
 	return doKeyboardHookHandler(wParam, lParam);
 }
 #endif