Support for IPP System Service

[andreaskem]

I would like to use python-ipp to query the list of printers on the system, as specified by Get-Printers in the IPP System Service. However, python-ipp seems to add a spurious printer-uri attribute and the request fails:

async with IPP(f'ipp://localhost:8000/ipp/system') as ipp:
    response = await ipp.execute(
        IppOperation.GET_PRINTERS,
        {
            'version': (2, 0),
            'operation-attributes-tag': {
                'system-uri': 'ipp://localhost:8000/ipp/system',
                'attributes-charset': 'utf-8',
                'attributes-natural-language': 'en-us',
                'requesting-user-name': 'ak',
            }
        },
    )

->

pyipp.exceptions.IPPError: ('Unexpected printer status code', {'status-code': 1030})

The request, as printed by the server, seems to have a printer-uri attribute and the system-uri attribute is missing.

HTTP_STATE_POST http://localhost:8000/ipp/system HTTP/1.1 ()
Get-Printers request: IPP/2.0 request-id=89387
Get-Printers request: operation-attributes-tag
Get-Printers request:   attributes-charset charset utf-8
Get-Printers request:   attributes-natural-language naturalLanguage en-us
Get-Printers request:   printer-uri uri ipp://localhost:8000/ipp/system
Get-Printers request:   requesting-user-name nameWithoutLanguage ak
Get-Printers client-error-not-found (printer-uri ipp://localhost:8000/ipp/system not found.)
OK application/ipp 148
Get-Printers response: IPP/2.0 request-id=89387, status-code=client-error-not-found
Get-Printers response: operation-attributes-tag
Get-Printers response:   attributes-charset charset utf-8
Get-Printers response:   attributes-natural-language naturalLanguage en-us
Get-Printers response:   status-message textWithoutLanguage printer-uri ipp://localhost:8000/ipp/system not found.
Closing connection from 'localhost'.

How do I get this to work? Is this even supported?