UnrealScript MQTT Client

A simple MQTT client implemented in UnrealScript for Unreal Tournament (possibly works with other Unreal Engine 1 games as well).

The following MQTT protocol features are supported:

• MQTT version 5.0
• Message publishing
• Message subscriptions with basic topic filter support
• QoS level 1 support
• Basic authentication (username and password)

With these limitations:

• Maximum packet size of 1024 bytes
• Only supports plain text messages (custom or binary formats can be implemented)
• Can't publish retained messages
• Most message, subscription, and connection properties don't do anything

Usage

To use the MQTT client in UnrealScript projects, spawn it, owned by one of your own actors. When it's connected, it will trigger its owner. Eg:

class MyThing extends Actor;

var private MQTTClient mqtt;

function PostBeginPlay() {
	mqtt = Spawn(class'MQTTClient', Self);
}

event Trigger(Actor Other, Pawn EventInstigator) {
	// the MQTTClient will trigger its owner when it has connected successfully
	if (Other == mqtt) {
		// you may now publish messages
		mqtt.publish("mytopic", "Hello World");
	}
}

If you want to subscribe to a topic, you will need to implement a subscriber actor which extends MQTTSubscriber.

When spawned, Subscribers should be owned by the MQTTClient, thereby allowing the client to manage the subscriptions based on the actor's lifecycle (eg. destroying the actor will cause the client to unsubscribe from a topic it was using).

You may spawn an MQTTSubscriber at any time, it does not need to wait for a connection to be established - subscriptions will be automatically created if and when the client connects.

Your MQTTSubscriber may implement whatever logic you want to react to received messages, or it may simply act as a shim between your code and the MQTT Client. Eg:

class MyTopicSubscriber extends MQTTSubscriber;

event subscribed() {
	log("I'm alive!");
}

event receiveMessage(String topic, String message) {
	log("Got a message on topic " $ topic $ ": " $ message);
	// do interesting things in the game based on the message
}

defaultproperties {
	topic="mytopic/#"
}

Then create an instance of it:

class MyThing extends Actor;

var private MQTTClient mqtt;
var private MyTopicSubscriber subscriber;

function PostBeginPlay() {
	mqtt = Spawn(class'MQTTClient', Self);
	subscriber = Spawn(class'MyTopicSubscriber', mqtt);
}

Configuration

In your game or server's UnrealTournament.ini file, append the configuration:

[MQTTClient.MQTTClient]
mqttHost=broker.hivemq.com
mqttPort=1883
sessionTtl=60
mqttUser=
mqttPass=
clientIdent=utserver
debugLog=false

Obviously provide your own private MQTT host if available, otherwise HiveMQ's public broker is handy for testing - just be sure to use unique topic names, and be aware that everything published there is public.