voidsipp · Nov 3, 2026
diff --git a/src/native/windows/clipboard.rs b/src/native/windows/clipboard.rs
@@ -1,3 +1,4 @@
+use winapi::shared::minwindef::HGLOBAL;
 use winapi::um::winbase::{GlobalAlloc, GlobalLock, GlobalSize, GlobalUnlock, GMEM_MOVEABLE};
 use winapi::um::winuser::CF_UNICODETEXT;
 use winapi::um::winuser::{
@@ -25,6 +26,16 @@ impl Drop for ClipboardGuard {
     }
 }
 
+struct GlobalUnlockGuard(HGLOBAL);
+
+impl Drop for GlobalUnlockGuard {
+    fn drop(&mut self) {
+        unsafe {
+            GlobalUnlock(self.0);
+        }
+    }
+}
+
 unsafe fn get_raw_clipboard() -> Option<Vec<u16>> {
     // https://docs.microsoft.com/en-us/windows/win32/dataxchg/about-the-clipboard
 
@@ -41,11 +52,16 @@ unsafe fn get_raw_clipboard() -> Option<Vec<u16>> {
         return None;
     }
 
+    read_clipboard_data(clipboard_data)
+}
+
+unsafe fn read_clipboard_data(clipboard_data: HGLOBAL) -> Option<Vec<u16>> {
     let data_ptr = GlobalLock(clipboard_data) as *const u16;
     if data_ptr.is_null() {
         return None;
     }
-    let data_size = GlobalSize(clipboard_data) as usize;
+    let _lock_guard = GlobalUnlockGuard(clipboard_data);
+    let data_size = GlobalSize(clipboard_data) / std::mem::size_of::<u16>();
 
     let slice = std::slice::from_raw_parts(data_ptr, data_size);
     let len = slice.iter().position(|b| *b == 0).unwrap_or(data_size);
@@ -100,3 +116,66 @@ impl crate::native::Clipboard for WindowsClipboard {
         }
     }
 }
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use winapi::um::winbase::{GlobalFlags, GlobalFree, GMEM_LOCKCOUNT};
+
+    struct Allocation(HGLOBAL);
+
+    impl Drop for Allocation {
+        fn drop(&mut self) {
+            unsafe {
+                GlobalFree(self.0);
+            }
+        }
+    }
+
    #[test]
+    fn reading_clipboard_data_releases_the_memory_lock() {
+        unsafe {
+            let text = "hello 🦀\0ignored".encode_utf16().collect::<Vec<_>>();
+            let allocation = Allocation(GlobalAlloc(GMEM_MOVEABLE, text.len() * 2));
+            assert!(!allocation.0.is_null());
+            let data = GlobalLock(allocation.0) as *mut u16;
+            assert!(!data.is_null());
+            ptr::copy_nonoverlapping(text.as_ptr(), data, text.len());
+            GlobalUnlock(allocation.0);
+            for _ in 0..3 {
+                assert_eq!(
+                    read_clipboard_data(allocation.0).unwrap(),
+                    "hello 🦀".encode_utf16().collect::<Vec<_>>()
+                );
+                assert_eq!(GlobalFlags(allocation.0) & GMEM_LOCKCOUNT, 0);
+            }
+        }
+    }
+
+    #[test]
+    fn unterminated_clipboard_data_stays_within_the_allocation() {
+        unsafe {
+            let allocation = Allocation(GlobalAlloc(GMEM_MOVEABLE, 16));
+            assert!(!allocation.0.is_null());
+            let data = GlobalLock(allocation.0) as *mut u8;
+            assert!(!data.is_null());
+            let size = GlobalSize(allocation.0);
+            ptr::write_bytes(data, 0x41, size);
+            GlobalUnlock(allocation.0);
+            assert_eq!(
+                read_clipboard_data(allocation.0).unwrap(),
+                vec![0x4141; size / 2]
+            );
+            assert_eq!(GlobalFlags(allocation.0) & GMEM_LOCKCOUNT, 0);
+        }
+    }
+
+    #[test]
+    fn discarded_clipboard_data_does_not_get_locked() {
+        unsafe {
+            let allocation = Allocation(GlobalAlloc(GMEM_MOVEABLE, 0));
+            assert!(!allocation.0.is_null());
+            assert!(read_clipboard_data(allocation.0).is_none());
+            assert_eq!(GlobalFlags(allocation.0) & GMEM_LOCKCOUNT, 0);
+        }
+    }
+}