Implementing manual duplex in a filter

[ValdikSS]

A printer I'm writing a filter (driver) for supports manual duplex in a sense that it has a button on the printer, which you can handle (and light the LED of it) from the filter.

The printer operates on a page printing level, each page is streamed to the printer during the printing process. This means that my filter needs to receive cups-raster data prepared for manual printing:

• odd pages first
• some kind of a signal that odd pages have ended
• 180°-rotated even pages second, in reverse

I could not find a way to force cups or cups-filters to do that. Is that supported?
I could only think of intermediate filter (possibly with foomatic) which would do that, but I'd like to avoid this approach.

[michaelrsweet]

There isn't a way to automatically support manual duplex via the standard filters.

[jsmeix]

I think for things which happen synchronously with the printer device
(like handling LEDs and buttons on the printer device)
a usual filter is the wrong place because usual filters
are not meant to communicate directly with the printer device.
But CUPS backends are meant to communicate directly with the printer device.

So a totally offhanded idea is
to implement that as a special CUPS backend.
The backend gets the final printer specific data via stdin
from the last filter so - at least in theory - it could
inspect that data and as needed "trigger the right things"
on the printer device for manual duplex, in particular the
backend can stop and continue sending data to the printer
as needed.

For basic info about making custom backends you may have a look
at the rather old but in general still valid article
"Using Your Own Backends to Print with CUPS"
https://en.opensuse.org/SDB:Using_Your_Own_Backends_to_Print_with_CUPS

Perhaps for "180°-rotated even pages" you may need
additionally a special filter, cf.
"Using Your Own Filters to Print with CUPS"
https://en.opensuse.org/SDB:Using_Your_Own_Filters_to_Print_with_CUPS

Of course this way it is more a hack to make things work
for a specific personal use case than a generic solution.