MakoIoT.Device.Services.Messaging 1.0.40.35009

Mako-IoT.Device.Services.Messaging

Message bus with pub-sub and stronly typed data contracts.

Main concepts

Message routing

There are two type of routes:

• Broadcast messages are published under topics and delivered to one or more subscribers. This is usually used for propagating events.
• Direct message is delivered to single recipient. This is usually used for sending commands. Routing is done automatically based on message types.

Message contracts

Message contracts are classes that implement IMessage interface. MessageType must be set to full type name of the class.

public class BlinkCommand : IMessage
{
    public BlinkCommand()
    {
        MessageType = this.GetType().FullName;
    }
    public bool LedOn { get; set; }
    public string MessageType { get; set; }
}

Consumers

Messages are delivered to consumer classes.

public class BlinkCommandConsumer : IConsumer
{
    private readonly IBlinker _blinker;
    private readonly ILogger _logger;

    public BlinkCommandConsumer(IBlinker blinker, ILogger logger)
    {
        _blinker = blinker;
        _logger = logger;
    }

    public void Consume(ConsumeContext context)
    {
        var cmd = (BlinkCommand)context.Message;
        _logger.LogDebug($"Setting LED to {cmd.LedOn}");
        _blinker.Set(cmd.LedOn);
    }
}

Consumers are registered against message types in DeviceBuilder with AddDirectMessageConsumer or AddSubscriptionConsumer

public static void Main()
{
    DeviceBuilder.Create()
        .AddMessageBus(o =>
        {
            o.AddDirectMessageConsumer(typeof(BlinkCommand), typeof(BlinkCommandConsumer), ConsumeStrategy.LastMessageWins);
        })
   //[...]

Consume strategies

Consuming multiple messages of same type (i.e. by single consumer) may be done in one of three fashions:

1. Synchronously - receiving subsequent messages is blocked until current message ends processing.
2. FIFO - received messages are put onto a queue and processed in order.
3. Last Message Wins - the most recent message is processed and older unprocessed messages are discarded. This equivalent to bulkhead resilience pattern with single concurrent action.

Sending messages

bus.Send(msg, "device1"); //sends direct message to "device1"
bus.Publish(msg); //publishes broadcast message

Interoperability with .NET

With .NET implementation of message bus you can easily communicate between nanoFramework devices and .NET services or application. Data contract classes can be shared across both parties. See messaging sample.