Transformation

In addition to passing the payload received via MQTT to a service, mqttwarn allows you do do the following:

• Transform payloads on a per/topic basis. For example, you know you'll be receiving JSON, but you want to warn with a nicely formatted message.
• For certain services, you can change the title (or subject) of the outgoing message.
• For certain services, you can change the priority of the outgoing message.

Consider the following JSON payload published to the MQTT broker:

mosquitto_pub -t 'osx/json' -m '{"fruit":"banana", "price": 63, "tst" : "1391779336"}'

Using format we can configure mqttwarn to transform that JSON into a different outgoing message which is the text that is actually notified. Part of said format looks like this in the configuration file, and basically specifies that messages published to osx/json should be transformed as on the right-hand side.

format = "I'll have a {fruit} if it costs {price}"

(Embedded "\n" are converted to newlines on output.)

The result is:

You associate MQTT topic branches to applications in the configuration file (copy mqttwarn.ini.sample to mqttwarn.ini for use). In other words, you can accomplish, say, following mappings:

• PUBs to owntracks/jane/iphone should be notified via Pushover to John's phone
• PUBs to openhab/temperature should be Tweeted
• PUBs to home/monitoring/alert/+ should notify Twitter, Mail, and Prowl

See details in the config sample for how to configure this script. The path to the configuration file (which must be valid Python) is obtained from the MQTTWARNINI environment variable which defaults to mqttwarn.ini in the current directory.