Crash on drag and drop: QUrl constructor failure in dropEvent

[Fadel-ai-glitch]

Bug Report: ITK-SNAP crashes on drag and drop (QUrl constructor failure)

Environment

• ITK-SNAP Version: 4.4.0-20250909-Linux-gcc64
• OS: CachyOS (Arch-based Linux)
• Qt Version: Qt6 (libQt6Core.so.6, libQt6Widgets.so.6, libQt6Gui.so.6)
• Installation Path: /opt/itksnap-4.4.0-20250909-Linux-gcc64/

Description

ITK-SNAP crashes immediately and consistently when performing a drag and drop operation of any file (images, DICOM folders, etc.) into the main window. The application terminates without any error dialog or recovery option.

Steps to Reproduce

1. Launch ITK-SNAP 4.4.0
2. Drag any image file (NIfTI, DICOM, etc.) from file manager
3. Drop the file onto the ITK-SNAP main window
4. Result: Application crashes immediately

Expected Behavior

The drag and drop should:

• Open the file dialog to select import options
• Load the image into ITK-SNAP
• Display the image in the viewer

Actual Behavior

• Application crashes with segmentation fault
• No error dialog is shown
• Application terminates completely

Stack Trace

From journalctl logs, the crash occurs in the dropEvent handler:

Stack trace of thread:
#0  0x00007fc8da95b304 _ZN4QUrlC1ERKS_ (libQt6Core.so.6 + 0x15b304)
#1  0x000055d057122a7a _ZN15MainImageWindow9dropEventEP10QDropEvent (/opt/itksnap-4.4.0-20250909-Linux-gcc64/lib/snap-4.4.0/ITK-SNAP + 0x1121a7a)
#2  0x00007fc8dc9f0a6e _ZN7QWidget5eventEP6QEvent (libQt6Widgets.so.6 + 0x1f0a6e)
#3  0x00007fc8dc9907b6 _ZN19QApplicationPrivate13notify_helperEP7QObjectP6QEvent (libQt6Widgets.so.6 + 0x1907b6)
#4  0x00007fc8dc9999fd _ZN12QApplication6notifyEP7QObjectP6QEvent (libQt6Widgets.so.6 + 0x1999fd)
#5  0x00007fc8da97c9e2 _ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent (libQt6Core.so.6 + 0x17c9e2)
#6  0x00007fc8dca0634e n/a (libQt6Widgets.so.6 + 0x20634e)
#7  0x00007fc8dca0700d n/a (libQt6Widgets.so.6 + 0x20700d)
#8  0x00007fc8dc9907b6 _ZN19QApplicationPrivate13notify_helperEP7QObjectP6QEvent (libQt6Widgets.so.6 + 0x1907b6)
#9  0x00007fc8da97c9e2 _ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent (libQt6Core.so.6 + 0x17c9e2)
#10 0x00007fc8dbde97f3 _ZN22QGuiApplicationPrivate11processDropEP7QWindowPK9QMimeDataRK6QPoint6QFlagsIN2Qt10DropActionEES8_INS9_11MouseButtonEES8_INS9_16KeyboardModifierEE (libQt6Gui.so.6 + 0x1e97f3)
#11 0x00007fc8dbe4a885 _ZN22QWindowSystemInterface10handleDropEP7QWindowPK9QMimeDataRK6QPoint6QFlagsIN2Qt10DropActionEES8_INS9_11MouseButtonEES8_INS9_16KeyboardModifierEE (libQt6Gui.so.6 + 0x24a885)

Root Cause

The crash occurs in MainImageWindow::dropEvent at line 1381 in GUI/Qt/Windows/MainImageWindow.cxx. The issue appears to be in the QUrl copy constructor (_ZN4QUrlC1ERKS_), suggesting a memory management issue or improper URL handling.

Workaround

Use File → Open Images... (Ctrl+O) menu instead of drag and drop.

Related Issues

This appears to be related to ongoing drag and drop issues:

• ITK snap crashes when loading incorrect label file #154 - ITK snap crashes when loading incorrect label file
• ITK-snap master can not open DICOM #147 - ITK-snap master can not open DICOM (drag and drop issue)
• Dicom series instance drag/drop doesn't open dialog to select series #132 - Dicom series instance drag/drop doesn't open dialog

Additional Information

• The crash is reproducible 100% of the time
• It occurs with all file types (tested with various medical imaging formats)
• Using File → Open works perfectly with the same files
• Multiple crash dumps have been generated by systemd-coredump

Suggested Fix

Review the MainImageWindow::dropEvent() implementation for:

• Proper QUrl lifetime management
• Correct copy/move semantics with Qt6
• Null pointer checks before URL operations
• Exception handling around MIME data processing

Would appreciate any guidance or patches for this critical usability issue.