Do I understand correctly that you have control over both ends of the transfer? If so... and keeping in mind I don't have the foggiest clue what XCOM is if not a really cool turn-based, alien-hunting, squad level combat game... shouldn't just comparing the size of the files net you the desired result?

As the above suggestions point out, sleep'g would be involved, but I don't see the need for module use if you have known file sizes.