Examples

This section contains some examples of how mqttwarn can be used with some more complex configurations.

Low battery notifications

By subscribing to your [OwnTracks] topic and adding the following custom filter you can get mqttwarn to send notifications when your phone battery gets below a certain level;

def owntracks_battfilter(topic, message):
    data = dict(json.loads(message).items())
    if data['batt'] is not None:
        return int(data['batt']) > 20
    return True

Now simply add your choice of target(s) to the topic's section and a nice format string and you are done;

[owntracks/#]
targets = pushover, xbmc
filter = owntracks_battfilter()
format = My phone battery is getting low ({batt}%)!

Producing JSON

Assuming we get, from an Arduino, say, a single numerical value in the payload of an MQTT message, we want to generate JSON with some additional fields. Using a Jinja2 template for the task, does exactly what we need:

The following target configuration invokes the template:

[arduino/temp]
targets = log:info, http:graylog2
template = temp2json.json

The Jinja2 template looks like this:

{#
    We expect a single numeric temperature value in `payload'
    Return JSON suitable for Graylog2 (requires host and short_message)

    Define a data structure in Jinja2 and return it as a JSON string.
    Note how transformation data (produced within mqttwarn) is used:
    the variables `_dtiso' and `payload' contain a timestamp and our
    payload respectively.
#}
{% set data = {
	'host'		: topic,
	'short_message'	: "Heat " + payload,
	'tst'		: _dtiso,
	'temperature'	: payload,
	'woohooo'	: 17,
	}
	%}
{{ data | jsonify }}

and an example JSON string returned by that template is then passed to our configured targets thusly:

"host": "arduino/temp", "woohooo": 17, "tst": "2014-04-13T09:25:46.247150Z", "temperature": "22", "short_message": "Heat 22"}

More examples

• agi-mqtt catches missed Asterisk calls and publishes them to MQTT from which mqttwarn reports them
• Forward Irrsi highlights