[cups-devel] How to constantly monitor local printer status

[Daniel Wagener]

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Hello list,

I was wondering how some printers manage to propagate their state to
the server without a job running. I.e. the user will see cover-open
almost as soon as the cover is opened on the printer even when the
printer is idle.

I know I can query a printer using a comand filter by sending a
commandfile, but that requires an action from the other side of the
backend.

As far as I can tell, one would need a program that constantly polls
the printer via the backend (as not every printer sends data to the
backend when not explicitly queried), however that certainly can't be
a print job, as this would block the queue or require to repeat a
print/command job at some interval.

In the list's archive I stumbled upon a mail that stated, that it was
planned to have port monitors do exactly this, however, the
documentation does not mention port monitors besides the usual filter
chain when doing a print or command job.

Searching for "printer state" seems to always end up at "filter and
backend programming", but again that only explains it in context of a
print job.

Is there a way to constantly poll printers using CUPS? Did I miss
something?


Regards

  Daniel Wagener
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