hdrachmann / Topos

:cyclone: .NET Event Processing library

Topos

It's something with topics.

Producing messages

Could e.g. be Apache Kafka, where we send a JSON-serialized message:

var producer = Configure
    .Producer(c => c.UseKafka("kafkahost01:9092", "kafkahost02:9092"))
    .Serialization(s => s.UseNewtonsoftJson())
    .Topics(m => m.Map<SomeEvent>("someevents"))
    .Create();

// keep producer instance for the entire life of your app,
// remembering to dispose it when we shut down
Using(producer);

// send events like this:;
await producer.Send(new SomeEvent("This is just a message"), partitionKey: "customer-004");

Let's go through the different configuration parts:

// Topos configurations start with 'Configure.', no matter what you want to configure
var producer = Configure

    // we configure a producer that uses Kafka, seeding it with a couple of brokers
    .Producer(c => c.UseKafka("kafkahost01:9092", "kafkahost02:9092"))

    // tell Topos to JSON-serialize messages
    .Serialization(s => s.UseNewtonsoftJson())

    // map .NET types of type SomeEvent to the 'someevents' topic
    .Topics(m => m.Map<SomeEvent>("someevents"))

    // creates the producer
    .Create();

Consuming messages

Let's also use Kafka to consume messages... the configuration is probably not that surprising to you, it's just Configure. and then let the fluent API guide you.

Check this out - here we set up a corresponding consumer that just prints out the contents from the received messages:

var consumer = Configure
    .Consumer("default-group", c => c.UseKafka("kafkahost01:9092", "kafkahost02:9092"))
    .Serialization(s => s.UseNewtonsoftJson())
    .Topics(t => t.Subscribe("someevents")
    .Positions(p => p.StoreInMongoDb("mongodb://mongohost01/some_database", "Positions"))
    .Handle(async (messages, token) =>
    {
        foreach (var message in messages)
        {
            switch (message.Body)
            {
                case SomeEvent someEvent:
                    Console.WriteLine($"Got some event: {someEvent}");
                    break;
            }
        }
    })
    .Start();

// dispose consumer when you want to stop consuming messages
Using(consumer);

Let's go through the configuration again:

// start with 'Configure.'...
var consumer = Configure

    // configure a consumer instance as part of the group 'default-group', and use Kafka
    .Consumer("default-group", c => c.UseKafka("kafkahost01:9092", "kafkahost02:9092"))

    // use JSON
    .Serialization(s => s.UseNewtonsoftJson())

    // subscribe to 'someevents'
    .Topics(t => t.Subscribe("someevents"))

    // store positions in MongoDB
    .Positions(p => p.StoreInMongoDb("mongodb://mongohost01/some_database", "Positions"))

    // handle messages
    .Handle(async (messages, token) =>
    {
        foreach (var message in messages)
        {
            switch (message.Body)
            {
                case SomeEvent someEvent:
                    Console.WriteLine($"Got some event: {someEvent}");
                    break;
            }
        }
    })
    .Start();