I wonder how hard it is to make a fake USB printer.
Like, a printer that takes any printout and goes "yep, that printed just fine" but nothing ever comes out anywhere

@foone Look at the code from the retro printer project, It does similar but for parallel printers as input and outputs to USB/Network printers.

Might be some bits you could borrow

https://www.retroprinter.com/

About the Retro-Printer Module | RetroPrinter.com

The Retro-Printer provides low cost printer port capture hardware to capture data and connect computers & industrial equipment to modern printers.

RetroPrinter.com
@ben @foone okay yeah we made a cheap joke elsewhere in the thread, which everyone else already made, so let us redeem ourselves by mentioning that we know enough about those old protocols to suspect it really is nearly the same except for a USB wrapper