Readfile hangs while trying to read the response from printer

By default, if you don't have a printer/scanner attached to your computer, the port is recognized as old SPP type parallel port.

If you using writefile(), the file is write to SPP output buffer and wait for parallel port to response and output to the port. The device must follow the handshaking transfer between device and PC to get data.

If a parallel port support IEEE-1284 standard, it will allow file transfer from printer thru predefined method like nibble mode, Byte mode, EPP mode or ECP mode.

The device must predefined what time to send data to the parallel port in buffer upon any data request. If your printer don't out something after the host request, it mean your printer just don't output or unlikely to output in this manner.

Then there are nothing to read, readfile() waiting for device to give respond: "Hello, printer, give me some data please."

You probably want to try to readfile() from a scanner and see if it actually work.