The API of xcb::Connection has constructors which allow an arbitrary RawFd to be used as a socket connection. On either failure of these constructors or on the drop of Connection, it closes the associated file descriptor. Thus, a program which uses an OwnedFd (such as a UnixStream) as the file descriptor can close the file descriptor and continue to attempt using it or close an already-closed file descriptor, violating I/O safety.

Starting in version 1.6.0, xcb provides Connection::connect with fd and Connection::connect with fd and extensions as safe alternatives and deprecates the problematic functions.