RAR archives can have a "locked" property essentially making them readonly. Currently, Ark doesn't handle this properly and fails silently if the user tries to modify the archive (e.g. adding files).
See bug 368851. Note that the archive mentioned in this bug opens as readonly due the file permissions being 400.
This diff adds a virtual method ReadOnlyArchiveInterface::isLocked() with a default implementation returning false. The method is overridden by the RAR plugin which checks if the archive is locked when listing. ReadWriteArchiveInterface::isReadOnly() checks isLocked() when determining the readonly status of the archive.
Currently, the user is not notified that the archive is locked. Maybe this should be exposed somewhere in the GUI.