Expose duplex capability via IPP (sides-supported) for duplex-capable Brother printers

[jpmanuell]

Hi, and thank you for brlaser — it’s been rock-solid for basic printing.

I’m running brlaser v6 on a modern CUPS 2.4 system and using it as a network print server
(USB-connected Brother printer shared via IPP / mDNS).

The printer (Brother DCP-B7500D, similar to DCP-7055 series) physically supports duplex,
and brlaser is able to perform duplex printing when explicitly requested (e.g. via
macOS or forced defaults).

However, brlaser does not advertise duplex capability via IPP attributes.
Specifically, the printer does not expose:

sides-supported = two-sided-*

As a result:

• Android / Mopria does not show a “Double-sided” option at all
• Mopria behaves correctly according to IPP, but duplex is effectively unavailable
• Administrators cannot safely enable duplex for strict IPP clients

Attempts to inject sides-supported via lpadmin are ignored (as expected on modern CUPS),
so this appears to be a driver capability-advertisement limitation rather than configuration.

This is not a bug report — printing works — but a feature request:
would it be possible for brlaser to advertise duplex capability via IPP
for models that are known to support duplex, e.g. by exposing appropriate
sides-supported attributes?

This would significantly improve compatibility with Android/Mopria and other
strict IPP clients, without changing default behavior.

If helpful, I’m happy to test patches or provide detailed IPP dumps
(ipptool get-printer-attributes) from a real device.

Thanks again for maintaining this driver.