Github user dlaboss commented on a diff in the pull request:
https://github.com/apache/incubator-quarks/pull/67#discussion_r58390932
--- Diff:
samples/connectors/src/main/java/quarks/samples/connectors/iotf/IotfSensors.java
---
@@ -109,6 +99,31 @@ public static void simulatedSensors(IotDevice device,
boolean print) {
// with event identifier "sensors".
device.events(sensors, "sensors", QoS.FIRE_AND_FORGET);
}
+
+ /**
+ * Create a heart beat device event with
+ * identifier {@code heartbeat} to
+ * ensure there is some immediate output and
+ * the connection to IoTF happens as soon as possible.
+ * @param device IoT device
+ */
+ public static void heartBeat(IotDevice device, boolean print) {
--- End diff --
I guess the comment could just add something like "If you are using an
MQTT-based IotDevice, you may want to consider using the MQTT KeepAlive and
LastWillAndTestament mechanisms instead of an explicit heartbeat." ?
It's true that this heartbeat provides a visible last-heartbeat-timestamp
to clients. However, a visible&reliable "I'm still connected" status seems to
be possible using just the KA/LWT.
That HiveMQ reference suggests: with a "retained" LWT to a topic "status"
with the value "offline", the device initially sends a *single* retained msg
"online" to that topic. Clients will see/receive "online" until the device is
no longer connected, at which point they will receive "offline" (by virtue of
the KA-induced LWT). I think there's also an implied: upon graceful shutdown,
the device sends a single retained "offline" to "status".
Regardless, should an issue be created to discuss (or track) adding
something to IotDevice for this higher level concept/feature, and to the
MqttDevice and IotfDevice impls? Don't know if something like this is already
part of the Watson IoT framework.
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