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Using the Message Bus
ToMCAT implements the Testbed Message Bus using the Mosquitto (MQTT) application. The system works over TCP/IP and provides a lightweight, robust infrastructure for interprocess communication. Messages are written to the Message Bus by publishing them to topics. Messages are read by subscribing to topics. Message arrival is handled by asynchronous callback.
There are three components to the MQTT system.
| Application name | Role | Description |
|---|---|---|
| mosquitto | Broker | Coordinator for subscription and publication. A single instance is run. |
| mosquitto_sub | Reader | Subscribes to topics on the Message Bus. Prints to stdout any messages it receives on the subscribed topics. n instances may be run. |
| mosquitto_pub | Writer | Publishes messages to topics on the Message Bus. n instances may be run. |
sudo apt-get update sudo apt-get install -y mosquitto mosquitto-clients
sudo port install mosquitto
or
sudo brew install mosquitto
- ToMCAT uses the MQTT default host 'localhost', and the MQTT default port '1883'.
- No password is used.
sudo service mosquitto start
No output is show on screen
/opt/local/sbin/mosquitto -c /opt/local/etc/mosquitto//mosquitto.conf
If the broker starts correctly it will output some status information:
1619221743: mosquitto version 1.5.8 starting
1619221743: Config loaded from /opt/local/etc/mosquitto//mosquitto.conf.
1619221743: Opening ipv6 listen socket on port 1883.
1619221743: Opening ipv4 listen socket on port 1883.
First start the Message bus using the previously described procedure for your operating system.
Next, subscribe to a Message Bus topic:
mosquitto_sub -t my_test_topic
Then publish a message on that topic:
mosquitto_pub -t my_test_topic -m "Hello world!"
If the mosquitto_sub process displays the message, your message bus is running correctly.
sudo service mosquitto stop
Kill the process ID of the mosquitto broker:
ps -aux | grep mosquitto mosquit+ 866 0.0 0.0 28112 4164 ? Ssl 11:13 0:05 /opt/local/sbin/mosquitto -c
/opt/local/etc/mosquitto/mosquitto.conf
kill 866