From 252d11a3169788ebac986a6afdcace02b2226fd2 Mon Sep 17 00:00:00 2001
From: Pedro Navarro <pnavarro@netflix.com>
Date: Sat, 7 Dec 2024 14:19:57 -0800
Subject: [PATCH] feat: Windows, Use a clipboard format listener to monitor the
 clipboard

On Windows monitor the clipboard using a Clipboard format listener instead
of the legacy clipboard viewer chain, which was unreliable as it required
other programs to maintain the clipboard chain properly and couldn't
recover it any window in the clipboard viewer chain stopped responding
to messages.

Monitor the clipboard sequence number to not process the clipboard more
than once.
---
 src/lib/platform/MSWindowsScreen.cpp | 40 +++++++++++++---------------
 src/lib/platform/MSWindowsScreen.h   |  4 +--
 2 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/src/lib/platform/MSWindowsScreen.cpp b/src/lib/platform/MSWindowsScreen.cpp
index e9647fb21..f94c93c5f 100644
--- a/src/lib/platform/MSWindowsScreen.cpp
+++ b/src/lib/platform/MSWindowsScreen.cpp
@@ -119,7 +119,7 @@ MSWindowsScreen::MSWindowsScreen(
       m_screensaverNotify(false),
       m_screensaverActive(false),
       m_window(NULL),
-      m_nextClipboardWindow(NULL),
+      m_clipboardSequenceNumber(0),
       m_ownClipboard(false),
       m_desks(NULL),
       m_keyState(NULL),
@@ -237,7 +237,9 @@ void MSWindowsScreen::enable()
   );
 
   // install our clipboard snooper
-  m_nextClipboardWindow = SetClipboardViewer(m_window);
+  if (!AddClipboardFormatListener(m_window)) {
+    LOG((CLOG_DEBUG "failed to add the clipboard format listener: %d", GetLastError()));
+  }
 
   // track the active desk and (re)install the hooks
   m_desks->enable();
@@ -268,8 +270,9 @@ void MSWindowsScreen::disable()
   m_keyState->disable();
 
   // stop snooping the clipboard
-  ChangeClipboardChain(m_window, m_nextClipboardWindow);
-  m_nextClipboardWindow = NULL;
+  if (!RemoveClipboardFormatListener(m_window)) {
+    LOG((CLOG_DEBUG "failed to remove the clipboard format listener: %d", GetLastError()));
+  }
 
   // uninstall fix timer
   if (m_fixTimer != NULL) {
@@ -1021,23 +1024,20 @@ bool MSWindowsScreen::onPreDispatchPrimary(HWND, UINT message, WPARAM wParam, LP
 bool MSWindowsScreen::onEvent(HWND, UINT msg, WPARAM wParam, LPARAM lParam, LRESULT *result)
 {
   switch (msg) {
-  case WM_DRAWCLIPBOARD:
-    // first pass on the message
-    if (m_nextClipboardWindow != NULL) {
-      SendMessage(m_nextClipboardWindow, msg, wParam, lParam);
-    }
 
-    // now handle the message
-    return onClipboardChange();
+  case WM_CLIPBOARDUPDATE: {
+    DWORD clipboardSequenceNumber = GetClipboardSequenceNumber();
+    LOG(
+        (CLOG_DEBUG "clipboard update: sequence number %d, current %d", clipboardSequenceNumber,
+         m_clipboardSequenceNumber)
+    );
 
-  case WM_CHANGECBCHAIN:
-    if (m_nextClipboardWindow == (HWND)wParam) {
-      m_nextClipboardWindow = (HWND)lParam;
-      LOG((CLOG_DEBUG "clipboard chain: new next: 0x%08x", m_nextClipboardWindow));
-    } else if (m_nextClipboardWindow != NULL) {
-      SendMessage(m_nextClipboardWindow, msg, wParam, lParam);
+    if (clipboardSequenceNumber && (clipboardSequenceNumber != m_clipboardSequenceNumber)) {
+      m_clipboardSequenceNumber = clipboardSequenceNumber;
+      onClipboardChange();
     }
-    return true;
+    return 0; // message processed
+  }
 
   case WM_DISPLAYCHANGE:
     return onDisplayChange();
@@ -1430,7 +1430,7 @@ bool MSWindowsScreen::onDisplayChange()
   return true;
 }
 
-bool MSWindowsScreen::onClipboardChange()
+void MSWindowsScreen::onClipboardChange()
 {
   // now notify client that somebody changed the clipboard (unless
   // we're the owner).
@@ -1445,8 +1445,6 @@ bool MSWindowsScreen::onClipboardChange()
     LOG((CLOG_DEBUG "clipboard changed: %s owned", kAppId));
     m_ownClipboard = true;
   }
-
-  return true;
 }
 
 void MSWindowsScreen::warpCursorNoFlush(SInt32 x, SInt32 y)
diff --git a/src/lib/platform/MSWindowsScreen.h b/src/lib/platform/MSWindowsScreen.h
index d7284973f..6b0381352 100644
--- a/src/lib/platform/MSWindowsScreen.h
+++ b/src/lib/platform/MSWindowsScreen.h
@@ -192,7 +192,7 @@ private: // HACK
   bool onMouseWheel(SInt32 xDelta, SInt32 yDelta);
   bool onScreensaver(bool activated);
   bool onDisplayChange();
-  bool onClipboardChange();
+  void onClipboardChange();
 
   // warp cursor without discarding queued events
   void warpCursorNoFlush(SInt32 x, SInt32 y);
@@ -314,7 +314,7 @@ private:
   // clipboard stuff.  our window is used mainly as a clipboard
   // owner and as a link in the clipboard viewer chain.
   HWND m_window;
-  HWND m_nextClipboardWindow;
+  DWORD m_clipboardSequenceNumber;
   bool m_ownClipboard;
 
   // one desk per desktop and a cond var to communicate with it