mqtt-laucher

mqtt-launcher

mqtt-launcher is a Python program which subscribes to a set of MQTT topics and executes processes on the host it's running on. Launchable processes are configured on a per/wildcard basis, and they can be constrained to run only if a particular text payload is contained in the message.

For example, I can publish a message to my MQTT broker requesting mqtt-launcher create a particular semaphore file for me:

mosquitto_pub -t sys/file -m create

The configuration file must be valid Python and it is loaded once. It contains the topic / process associations.

# topic                     payload value       program & arguments
"sys/file"  :   {
                    'create'        :   [ '/usr/bin/touch', '/tmp/file.one' ],
                    'false'         :   [ '/bin/rm', '-f', '/tmp/file.one'    ],
                    'info'          :   [ '/bin/ls', '-l', '/tmp/file.one' ],
                },

Above snippet instructs mqtt-launcher to:

• subscribe to the MQTT topic sys/file
• look up the payload string and launch the associated programs:
  • if the payload is create, then touch a file
  • if the payload is the string false, remove a file
  • if the payload is info, return information on the file

mqtt-launcher publishes stdout and stderr of the launched program to the configured topic with /report added to it. So, in the example above, a non-retained message will be published to sys/file/report. (Note that this message contains whatever the command outputs; trailing white space is truncated.)

Screenshot

Here's the obligatory "screenshot".

Publishes					Subscribes
-----------------------------------		------------------------------------------------------------------
						$ mosquitto_sub -v -t 'dev/#' -t 'sys/file/#' -t 'prog/#' 


mosquitto_pub -t prog/pwd -n
						prog/pwd (null)
						prog/pwd/report /private/tmp

mosquitto_pub -t sys/file -m create
						sys/file create
						sys/file/report (null)	# command has no output

mosquitto_pub -t sys/file -m info
						sys/file info
						sys/file/report -rw-r--r--  1 jpm  wheel  0 Jan 22 16:10 /tmp/file.one

mosquitto_pub -t sys/file -m remove
						sys/file remove
						# report not published: subcommand ('remove') doesn't exist
						# log file says:
						2014-01-22 16:11:30,393 No matching param (remove) for sys/file

mosquitto_pub -t dev/1 -m hi
						dev/1 hi
						dev/1/report total 16231
						drwxrwxr-x+ 157 root  admin     5338 Jan 20 10:48 Applications
						drwxrwxr-x@   8 root  admin      272 Jan 25  2013 Developer
						drwxr-xr-x+  72 root  wheel     2448 Oct 14 10:54 Library
						...

Configuration

mqtt-launcher loads a Python configuration from the path contained in the environment variable $MQTTLAUNCHERCONFIG; if unset, the path defaults to launcher.conf. See the provided launcher.conf.example.

Logging

mqtt-launcher logs its operation in the file configured as logfile.

Requirements

• Python
• mosquitto.py

Credits

This program was inspired by mqtt-exec. I'm not terribly comfortable running NodeJS programs, so I implemented the idea in Python.