The workaround with IO::File worked fine, and it doesn't require the installation of external modules in recent perls. While probably not the best for long-term production code, I find it better for example scripts that can work with the least requirement for the user.

About open() you're right... probably. One of the thousands things I tried involved using File::Temp to get a temporary, "real-file" handle, but the readFromFileHandle() method continued to complain. I had to use the filename given back by File::Temp instead of the filehandle.