[Nut-upsuser] finding a common abstraction for reporting

[Greg Troxel]

I have been using NUT for a long time, but my UPS farm is very old and
homogenous: I have 3 "Best Power Fortress" from about 1995, and there's
one at someone else's.  (Yes, these really are 27 years old, and yes I
have changed the batteries.)  They report a bunch of variables, and I
have written a python program to report the interesting data over MQTT
for use in Home Assistant or whatever.  I mumbled earlier that I will
release that as open source and I mumble that again.

Nothing super interesting here:

  battery.runtime: 5940
  battery.runtime.low: 
  battery.voltage: 27.5
  battery.voltage.nominal: 24
  device.mfr: Best Power
  device.model: Fortress
  device.type: ups
  driver.name: bestfortress
  driver.parameter.baudrate: 9600
  driver.parameter.max_load: 660
  driver.parameter.pollinterval: 2
  driver.parameter.port: /dev/tty.ups
  driver.parameter.synchronous: no
  driver.version: 2.7.4
  driver.version.internal: 0.05
  input.frequency: 60.0
  input.transfer.high: 
  input.transfer.low: 
  input.voltage: 124
  output.current: 0.3
  output.voltage: 123
  output.voltamps: 37
  ups.delay.shutdown: 10
  ups.load: 5
  ups.mfr: Best Power
  ups.model: Fortress
  ups.status: OL 
  ups.temperature: 18

and it is turned into json (omitting much) as an MQTT payload:

{"tst":"2022-03-17T19:15:15.641791-0400","topic":"sensor/foo/bar-ups/json","qos":2,"retain":0,"payloadlen":233,"mid":27,"payload":{"time": 1647558915.5165293, "runtime": 5940.0, "battery": 27.5, "frequency": 60.0, "line_v": 124.0, "output_v": 123.0, "output_a": 0.3, "output_va": 37.0, "output_percent": 5.0, "status": "OL ", "utility": "ON", "temperature": 18.0}}

I know from past discussion that reporting "status" this way is
nonportable/awkward, and I probably should omit it and just use
"utility" which maybe should be "utility_inuse".  My point is that what
the monitoring system cares about is "Is the UPS using utility power or
not" as a running on battery even if input voltage is non-zero is still
cause for concern.

And maybe I should drop output_percent and have rated_va configured (660
in this case) because it doesn't seem to be in the NUT output.

My script is in the process of being extended to also deal with apcupsd
and that seems to have different variables, like timeleft in minutes
instead of runtime in seconds.  It seems obvious to me that I should
bring things into a common schema, because the monitoring system doesn't
care about UPS brand; it wants to know is utility power good enough, how
many seconds left, etc.

I wonder how much NUT does that by itself, or if it's more doing format
translation of the individual units.  And I would appreciate comments on
the wisdom/necessity of this approach.

Thanks,
Greg

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