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Developer that lives by the mantra "code is meant to be shared".




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Sampling messages from NATS using my C# client for NATS

Daniel WertheimDaniel Wertheim

I'm currently in the process of building a solution for controlling parts of my home, based on my current mood. The first source of sensor data is my own heart rate. I'm using it as input for controlling lights. Like changing colors etc. For dispatching the received heart rate to a light controller as well as a health indexer, I'm using NATS. The heart rate sensor gives me several readings each second and for the indexer I'm writing it down to a time series optimized database, InfluxDB. The data in turn is visualized in Grafana. The lamps are controlled by a separate application/service that also listens to the heart rates being published over NATS. The client I've built for NATS is based around IObservable<T>, hence it is RX friendly and we can therefore make use of Observable.Sample. This becomes really useful when controlling the lamps, as I don't want to react on each individual reading for setting new colors etc. I can instead make use of sampling and be picking one value over the period of lets say five seconds.

For simplicity of getting RX setup, install the convenience package that brings that in:

install-package MyNatsClient.RX  

Now just setup a subscription to a subject, in my case: "heartratereceived"; and start sampling messages:

var samplingFreq = TimeSpan.FromSeconds(5);

var cnInfo = new ConnectionInfo("LightsController", "");

var client = new NatsClient(cnInfo);  
  msgOps => msgOps
    .Select(msgOp => HearRateDataReceived.Parse(msgOp.GetPayloadAsString()))
    .Where(ev => _lastKnownBpm != ev.BeatPerMinute)
    .Subscribe(ev => AdjustColors(ev)));

Done! Happy sampling



Developer that lives by the mantra "code is meant to be shared".