From c2b852a512605f601a1caefc5498c66259233b31 Mon Sep 17 00:00:00 2001
From: Pierre Ossman <ossman@cendio.se>
Date: Tue, 14 Dec 2021 17:06:36 +0100
Subject: [PATCH] TEMP: handle macOS keyboard steal

---
 vncviewer/KeyboardMacOS.h  |  3 +++
 vncviewer/KeyboardMacOS.mm | 22 +++++++++++++++++++
 vncviewer/Viewport.cxx     | 43 +++++++++++++++++++++++++-------------
 vncviewer/Viewport.h       |  2 ++
 4 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/vncviewer/KeyboardMacOS.h b/vncviewer/KeyboardMacOS.h
index 5ebab7b5f..e61e26143 100644
--- a/vncviewer/KeyboardMacOS.h
+++ b/vncviewer/KeyboardMacOS.h
@@ -39,6 +39,9 @@ class KeyboardMacOS : public Keyboard {
   virtual unsigned getLEDState();
   virtual void setLEDState(unsigned state);
 
+  // Special helper on macOS
+  static bool isKeyboardSync(const void* event);
+
 protected:
   bool isKeyboardEvent(const NSEvent* nsevent);
   bool isKeyPress(const NSEvent* nsevent);
diff --git a/vncviewer/KeyboardMacOS.mm b/vncviewer/KeyboardMacOS.mm
index 62cdcdfcd..42964d3ac 100644
--- a/vncviewer/KeyboardMacOS.mm
+++ b/vncviewer/KeyboardMacOS.mm
@@ -296,12 +296,34 @@
   // No support for Scroll Lock //
 }
 
+bool KeyboardMacOS::isKeyboardSync(const void* event)
+{
+  const NSEvent* nsevent = (const NSEvent*)event;
+
+  assert(event);
+
+  // If we get a NSFlagsChanged event with key code 0 then this isn't
+  // an actual keyboard event but rather the system trying to sync up
+  // modifier state after it has stolen input for some reason (e.g.
+  // Cmd+Tab)
+
+  if ([nsevent type] != NSFlagsChanged)
+    return false;
+  if ([nsevent keyCode] != 0)
+    return false;
+
+  return true;
+}
+
 bool KeyboardMacOS::isKeyboardEvent(const NSEvent* nsevent)
 {
   switch ([nsevent type]) {
   case NSKeyDown:
   case NSKeyUp:
+    return true;
   case NSFlagsChanged:
+    if (isKeyboardSync(nsevent))
+      return false;
     return true;
   default:
     return false;
diff --git a/vncviewer/Viewport.cxx b/vncviewer/Viewport.cxx
index a48071b4a..2cc99c357 100644
--- a/vncviewer/Viewport.cxx
+++ b/vncviewer/Viewport.cxx
@@ -457,21 +457,8 @@ int Viewport::handle(int event)
     return 1;
 
   case FL_UNFOCUS:
-    // Release all keys that were pressed as that generally makes most
-    // sense (e.g. Alt+Tab where we only see the Alt press)
-    try {
-      cc->releaseAllKeys();
-    } catch (rdr::Exception& e) {
-      vlog.error("%s", e.str());
-      abort_connection(_("An unexpected error occurred when communicating "
-                         "with the server:\n\n%s"), e.str());
-    }
-    keyboard->reset();
-
-    hotKeyHandler.reset();
-    hotKeyBypass = false;
-    hotKeyActive = false;
-    pressedKeys.clear();
+    // We won't get more key events, so reset our knowledge about keys
+    resetKeyboard();
 
     //Fl::enable_im();
     return 1;
@@ -610,6 +597,24 @@ void Viewport::handlePointerTimeout(void *data)
   }
 }
 
+void Viewport::resetKeyboard()
+{
+  // Release all keys that were pressed as that generally makes most
+  // sense (e.g. Alt+Tab where we only see the Alt press)
+  try {
+    cc->releaseAllKeys();
+  } catch (rdr::Exception& e) {
+    vlog.error("%s", e.str());
+    abort_connection(_("An unexpected error occurred when communicating "
+                       "with the server:\n\n%s"), e.str());
+  }
+  keyboard->reset();
+
+  hotKeyHandler.reset();
+  hotKeyBypass = false;
+  hotKeyActive = false;
+  pressedKeys.clear();
+}
 
 void Viewport::handleKeyPress(int systemKeyCode,
                               rdr::U32 keyCode, rdr::U32 keySym)
@@ -807,6 +812,14 @@ int Viewport::handleSystemEvent(void *event, void *data)
   if (!self->hasFocus())
     return 0;
 
+#ifdef __APPLE__
+  // Special event that means we temporarily lost some input
+  if (KeyboardMacOS::isKeyboardSync(event)) {
+    self->resetKeyboard();
+    return 1;
+  }
+#endif
+
   consumed = self->keyboard->handleEvent(event);
   if (consumed)
     return 1;
diff --git a/vncviewer/Viewport.h b/vncviewer/Viewport.h
index 5e526161d..f6de5cebe 100644
--- a/vncviewer/Viewport.h
+++ b/vncviewer/Viewport.h
@@ -84,6 +84,8 @@ class Viewport : public Fl_Widget, protected EmulateMB,
   void handlePointerEvent(const rfb::Point& pos, int buttonMask);
   static void handlePointerTimeout(void *data);
 
+  void resetKeyboard();
+
   virtual void handleKeyPress(int systemKeyCode,
                               rdr::U32 keyCode, rdr::U32 keySym);
   virtual void handleKeyRelease(int systemKeyCode);