Friday, June 29, 2012


That's far too many acronyms, really. What do they mean? Well, readers of this blog will understand that TDI has got nothing to do with diesel engines but is, in fact, Tivoli Directory Integrator.

MQTT? MQ Telemetry Transport - "a machine-to-machine (M2M)/"Internet of Things" connectivity protocol".

RSMB? Really Small Message Broker - "a very small messaging server that uses the lightweight MQTT publish/subscribe protocol to distribute messages between applications".

So what do I want to do with this stuff? Well, you will now know that I got myself a Raspberry Pi and I was scratching around thinking of things I'd like my Pi to do. I came across an excellent video showing how Andy Stanford-Clark is utilising his Pi to monitor and control devices around his home - it is definitely worth a look

I have no intention (yet) of trying to copy Andy's achievements as I'm quite sure I don't have the spare hours in the day! However, I was intrigued to see if I could use my favourite tool (TDI) to ping messages to RSMB using MQTT.

Step 1 - Download RSMB

Step 2 - Startup RSMB

Step 3 - Fire up a Subscriber listening to the TDI topic

Step 4 - Write an Assembly Line to use the MQTT Publisher Connector

Step 5 - Populate the output map of my connector and run the Assembly Line.
The result will be a message published to RSMB which I can see in my subscriber utility:

I can also see the RSMB log shows the connections to the server:

Of course, TDI doesn't have an MQTT Publisher Connector - I had to write one. The good news is that this was possibly the simplest connector of all-time to write. That said, it is extra-ordinarily basic and is missing a myriad of features. For example - it does not support authentication to RSMB. It's error handling is what I can only describe as flaky. It is a publisher only - I haven't provided subscriber functions within the connector. But it shows how TDI could be used to ping very simple lightweight messages to a message broker using MQTT.

So what? Sounds like an intellectual exercise, right? Well, maybe. But MQTT is a great way of pushing information to mobile devices (as demonstrated by Dale Lane) so what I have is a means of publishing information from my running assembly lines to multiple mobile devices in real-time - potentially.

At this point, though, it is worth pointing out that the development of a connector is complete overkill for this exercise (though it does look pretty).

Dropping the wmqtt.jar file that can be found in the IA92 package into {TDI_HOME}/jars/3rdparty will allow you to publish to RSMB using the following few lines of TDI scripting:

// Let's create a MQTT client instance
var mqttpersistence = null;
var mqttclient ="tcp://rsmb-server:1883", mqttpersistence);

// Let's connect to the RSMB server and provide a ClientID
var mqttclientid = "tdi-server";
var mqttcleanstart = true;
var mqttkeepalive = 0;
mqttclient.connect(mqttclientid, mqttcleanstart, mqttkeepalive);

// Let's publish
var mqtttopic = "TDI";
var mqttmessage = "This is a sample message!";
var mqttqos = 0;
var mqttretained = false;
mqttclient.publish(mqtttopic, mqttmessage.getBytes("ISO-8859-1"), mqttqos, mqttretained);

Not very complicated. In fact, very simple indeed! (The connector I developed doesn't get very much more complicated than this!)

1 comment:

Andy Piper said...

Interesting, I'm not familiar with TDI. However, it is probably worth nothing that the wmqtt.jar that you are using is deprecated in favour of the Eclipse Paho Java client, which implements the full MQTT v3.1 specification including e.g. authentication, so you might want to take a look at that instead :-)