Moquette is to MQTT what inetd is to IP. Moquette listens for events from an MQTT broker and executes a process (event handler) found in its configuration directory if its name matches the event's topic. The matching obeys to the MQTT topic rules. Slashes in the topic are replaced by colon (:).

For instance, the following file names will all match the topic home/office/lamp/setOn:

• home:office:lamp:setOn
• home:office:+:setOn
• home:office:#
• #

Event handler files must be at the root of the Moquette configuration directory and have their executable flag set. The default directory is /etc/moquette.d and can be changed using the --conf option. New files can be added/removed while Moquette is running, without the need to restart it.

When an event handler is executed, Moquette sends the event payload as first argument to the command and the event topic is set as the $MQTT_TOPIC environment variable. The message ID is also transmitted using the $MQTT_MSGID environment variable.

A command can send events back by writing to the file descriptor number 3. The Format is as follow:

PUB <topic> <qos> <payload length>\n
<payload>

For instance, to send "hello world" on the example/somewhere topic using bash:

msg="hello world"
echo -e "PUB example/somewhere 0 ${#msg}\n$msg" >&3

Moquette will wait as long as necessary for the process to finish its execution. This way it is possible to delay the response to an event, or send multiple events spread in time to implement a timer for instance.

The examples below are written in bash, but handlers can be written in any language. You can find more examples in the conf directory.

#!/bin/bash

echo -e "PUB ${MQTT_TOPIC%*in}out 0 ${#1}\n$1" >&3

This handler responds to any event written on a matching topic, and sends back an event on the same topic by replacing in by out.

For instance, sending "hello world" to example/echo/test/in will send back "hello world" to the topic example/echo/test/out.

#!/bin/bash

# Kill concurrent run of ourselves
echo "KILL $MQTT_TOPIC" >&3

n=$1
while [ $n -ge 0 ]; do
    sleep 1
    echo -e "PUB ${MQTT_TOPIC%*set}tick 0 ${#n}\n$n" >&3
    ((n--))
done

This handler sends a tick every second for n seconds when n is sent to a matching topic. Ticks are sent on the same topic with the last set component replaced by tick.

Note that we introduced the KILL command here. A KILL followed by a topic, will kill all existing running commands that match the provided topic. The current process is never killed, even if the topic matches.

From source:

go get -u github.com/rs/moquette

Using docker (assuming the conf/ directory contains your handlers):

docker run -it --rm -v $(pwd)/conf:/etc/moquette.d poitrus/moquette -broker tcp://<broker_ip>:1883

All source code is licensed under the MIT License.