Jasper as Lightweight Service Bus

I’ve suddenly got some momentum going on Jasper, and I’m trying to keep up a steady pace of blog posts about it to try to get some visibility and see about possibly attracting some community around it. This tutorial is admittedly just taken from the documentation website.

Using its own built in TCP Transport, Jasper can be used as a very lightweight service bus to send messages asynchronously between Jasper applications. In this tutorial, we’re going to create two Jasper services that exchange messages with each either.

For the purpose of this tutorial, we’re going to heavily leverage the dotnet command line tools, so if you would, open your favorite command line tool.

The first step is just to ensure you have the latest Jasper project templates by installing JasperTemplates as shown below:

dotnet new -i JasperTemplates

Next, let’s build up a new .Net solution with these three projects:

1. Messages — just a class library that holds shared message types we’ll be sending back and forth.
2. Pinger — a Jasper service that will send PingMessage messages every 5 seconds
3. Ponger — a Jasper service that will receive PingMessage messages, and send a corresponding PongMessage back to the original sender service

To build out this new solution, you can use the following command line script and then open the newly created PingAndPong.sln file:

mkdir PingAndPong
cd PingAndPong

dotnet new classlib --name Messages
dotnet new jasper.service --name Pinger
dotnet new jasper.service --name Ponger

dotnet add Pinger/Pinger.csproj reference Messages/Messages.csproj

dotnet new sln

dotnet sln PingAndPong.sln add Messages/Messages.csproj Pinger/Pinger.csproj Ponger/Ponger.csproj

In the Messages Project

All we need to do in the Messages project is to add these message types for later:

public class PingMessage
{
    public Guid Id { get; set; }
    public string Name { get; set; }
}

public class PongMessage
{
    public Guid Id { get; set; }
    public string Name { get; set; }
}

In the Ponger Project

We need to make a couple changes to Ponger. First, open the generated JasperConfig class and add the line of code shown below to tell Ponger to listen for messages on port 3051:

    internal class JasperConfig : JasperRegistry
    {
        public JasperConfig()
        {
            Transports.LightweightListenerAt(3051);
        }
    }

Next, we need to handle the PingMessage message, and send a PongMessage back to the original sender:

public class PingHandler
{
    public Response Handle(PingMessage message)
    {
        ConsoleWriter.Write(ConsoleColor.Cyan, "Got a ping with name: " + message.Name);

        var response = new PongMessage
        {
            Name = message.Name
        };

        // Don't know if you'd use this very often,
        // but this is a special syntax that will send
        // the "response" back to the original sender
        return Respond.With(response).ToSender();
    }
}

In the Pinger Project

In Pinger, we need a handler for the PongMessage messages coming back, so add this class:

public class PongHandler
{
    public void Handle(PongMessage message)
    {
        ConsoleWriter.Write(ConsoleColor.Cyan, "Got a pong back with name: " + message.Name);
    }
}

We also need something that just runs in the background and sends PingMessage messages out. For that, we’ll use an implementation of ASP.Net Core’s IHostedService:

    // In this case, BackgroundService is a base class
    // for the IHostedService that is *supposed* to be
    // in a future version of ASP.Net Core that I shoved
    // into Jasper so we could use it now. The one in Jasper
    // will be removed later when the real one exists in
    // ASP.Net Core itself
    public class PingSender : BackgroundService
    {
        private readonly IMessageContext _bus;

        public PingSender(IMessageContext bus)
        {
            _bus = bus;
        }

        protected override Task ExecuteAsync(CancellationToken stoppingToken)
        {
            var count = 1;

            return Task.Run(async () =>
            {
                while (!stoppingToken.IsCancellationRequested)
                {
                    await Task.Delay(1000, stoppingToken);

                    await _bus.Send(new PingMessage
                    {
                        Name = "Message" + count++
                    });
                }
            }, stoppingToken);
        }
    }

Lastly in Pinger, open the JasperConfig class and add a single line of code shown below that directs Jasper to listen for messages using its TCP Transport at port 3050. We’ll also make a static publishing rule to publish all messages to the Ponger service. Lastly, we need to register the PingSender with the system so that it runs continuously when the application is started.

All that is shown below:

    internal class JasperConfig : JasperRegistry
    {
        public JasperConfig()
        {
            
            // Directs Jasper to use the TCP listener and
            // bind to port 3050. 
            Transports.LightweightListenerAt(3050);
            
            // Send all published messages to this location
            Publish.AllMessagesTo("tcp://localhost:3051");

            Services.AddSingleton<IHostedService, PingSender>();
        }
    }

Running Pinger and Ponger

Now you’ll want a pair of command windows open, one to the root directory of Pinger and one to Ponger.

Since it’s a little bit cleaner, start up Ponger first with a simple call to dotnet run from the Ponger directory and you should see output like this:

ComputerName:Ponger user$ dotnet run
dbug: Microsoft.AspNetCore.Hosting.Internal.WebHost[3]
      Hosting starting
Jasper 'Nullo' startup is being used to start the ASP.Net Core application
dbug: Microsoft.AspNetCore.Hosting.Internal.WebHost[4]
      Hosting started
dbug: Microsoft.AspNetCore.Hosting.Internal.WebHost[0]
      Loaded hosting startup assembly Ponger, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Running service 'JasperConfig'
Application Assembly: Ponger, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Hosting environment: Production
Content root path: /Users/jeremydmiller/code/PingAndPong/Ponger/bin/Debug/netcoreapp2.1/
Hosted Service: Jasper.JasperActivator
Hosted Service: Jasper.Messaging.Logging.MetricsCollector
Hosted Service: Jasper.Messaging.BackPressureAgent
Listening for loopback messages

Active sending agent to loopback://retries/
Handles messages:
  PingMessage: HandlerType: Ponger.PingHandler, Method: Jasper.Messaging.Runtime.Invocation.Response Handle(Messages.PingMessage)

Application started. Press Ctrl+C to shut down.

Then start Pinger with the same dotnet run command from the root of the Pinger project and well, you’ll get a boatload of logging like this:

dbug: Jasper.Messages[101]
      Received PongMessage#0168be78-ddcd-43b6-8fc4-15cc855354c3 at tcp://localhost:3050/ from tcp://localhost:3051/
Got a pong back with name: Message18
dbug: Jasper.Messages[102]
      Started processing PongMessage#0168be78-ddcd-43b6-8fc4-15cc855354c3
dbug: Jasper.Messages[103]
      Finished processing PongMessage#0168be78-ddcd-43b6-8fc4-15cc855354c3
info: Jasper.Messages[104]
      Successfully processed message PongMessage#0168be78-ddcd-43b6-8fc4-15cc855354c3 from tcp://localhost:3051/
dbug: Jasper.Messages[100]
      Sent PingMessage#0168be78-e0ed-4eec-8081-05e7b1f36006 to tcp://localhost:3051/
info: Jasper.Transports[204]
      Sending agent for tcp://localhost:3051/ has resumed
dbug: Jasper.Transports[200]
      Successfully sent 1 messages to tcp://localhost:3051/
dbug: Jasper.Transports[202]
      Received 1 message(s) from tcp://localhost:3051/
dbug: Jasper.Messages[101]
      Received PongMessage#0168be78-e1b9-4bc8-bc58-98cdccf9824b at tcp://localhost:3050/ from tcp://localhost:3051/
dbug: Jasper.Messages[102]
      Started processing PongMessage#0168be78-e1b9-4bc8-bc58-98cdccf9824b
Got a pong back with name: Message19
dbug: Jasper.Messages[103]
      Finished processing PongMessage#0168be78-e1b9-4bc8-bc58-98cdccf9824b
info: Jasper.Messages[104]
      Successfully processed message PongMessage#0168be78-e1b9-4bc8-bc58-98cdccf9824b from tcp://localhost:3051/
dbug: Jasper.Messages[100]
      Sent PingMessage#0168be78-e4da-4c36-95e3-aa9d15ee0ff2 to tcp://localhost:3051/
info: Jasper.Transports[204]
      Sending agent for tcp://localhost:3051/ has resumed
dbug: Jasper.Transports[200]
      Successfully sent 1 messages to tcp://localhost:3051/
dbug: Jasper.Transports[202]
      Received 1 message(s) from tcp://localhost:3051/
dbug: Jasper.Messages[101]
      Received PongMessage#0168be78-e5a7-4e03-9894-4c3f61ed7413 at tcp://localhost:3050/ from tcp://localhost:3051/
dbug: Jasper.Messages[102]
      Started processing PongMessage#0168be78-e5a7-4e03-9894-4c3f61ed7413
Got a pong back with name: Message20
dbug: Jasper.Messages[103]
      Finished processing PongMessage#0168be78-e5a7-4e03-9894-4c3f61ed7413
info: Jasper.Messages[104]
      Successfully processed message PongMessage#0168be78-e5a7-4e03-9894-4c3f61ed7413 from tcp://localhost:3051/
dbug: Jasper.Messages[100]
      Sent PingMessage#0168be78-e8c5-4130-a919-81bfe235becb to tcp://localhost:3051/
info: Jasper.Transports[204]
      Sending agent for tcp://localhost:3051/ has resumed
dbug: Jasper.Transports[200]
      Successfully sent 1 messages to tcp://localhost:3051/
dbug: Jasper.Transports[202]
      Received 1 message(s) from tcp://localhost:3051/
dbug: Jasper.Messages[101]
      Received PongMessage#0168be78-e991-41b9-b1f0-16ee2fa75377 at tcp://localhost:3050/ from tcp://localhost:3051/
dbug: Jasper.Messages[102]
      Started processing PongMessage#0168be78-e991-41b9-b1f0-16ee2fa75377
Got a pong back with name: Message21

Alright, you’ve got a fully functional system of two services who constantly chat with each other. For more information about the topics we covered in this tutorial, see the documentation for Messaging