messaging

An opinionated messaging library for simple pub/sub with different serialization and message broker/middleware.

To use this library, you need to decide on which serialization and messaging middleware to use.

Samples

This repository includes two samples:

Example publishing and handling a message on an ASP.NET Core application

// Class without annotations
public class SomeMessage
{
    public string Body { get; set; }
}

// Handling messages: Class implementing IMessageHandler<T> to be invoked when T arrives
public class SomeMessageHandler : IMessageHandler<SomeMessage>
{
    public Task Handle(SomeMessage message, CancellationToken _)
    {
        Console.WriteLine($"Handled: {message}.");
        return Task.CompletedTask;
    }
}

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddMessaging(builder => builder
        .AddRedis()
        .AddSerialization(b => b.AddProtoBuf())
        .AddTopic<SomeMessage>("some.topic"))
}
public void Configure(IApplicationBuilder app)
{
    app.UseMessagingSubscriptions(); // Subscribes to the topics defined via Services
}

// Publishing via ASP.NET Core MVC:
[Route("some-message")]
public class SomeMessageController
{
    private readonly IMessagePublisher _publisher;
    public SomeMessageController(IMessagePublisher publisher) => _publisher;

    [HttpPut]
    public async Task<IActionResult> PublishSomeMessage([FromBody] SomeMessage message, CancellationToken token)
    {
        await _publisher.Publish(message, token);
        return Accepted();
    }
}

Highlights

Supports multiple serialization formats and messaging middlewares.
Message handlers automatically discovered, registered
Handlers are resolved through DI with configurable lifetimes
Handler invocation done with Expression trees
Doesn't require implementing any interfaces or declaring attributes

Messaging middleware

The current supported messaging systems are:

Serialization

The supported serialization formats are:

MessagePack - with MessagePack-CSharp
ProtoBuf - with protobuf-net
JSON - with Newtonsoft.Json
XML - with System.Xml.XmlSerializer

All of the above can be 'plugged-in' with a single line when using the Messaging.DependencyInjection.* packages. Example serialization setup:

services.AddMessaging(builder =>
    builder.AddSerialization(s =>
    {
        s.AddMessagePack();
        // or
        s.AddProtoBuf();
        // or
        s.AddJson();
        // or
        s.AddXml();
    })

Each implementation has some additional settings.

For more information on serialization, please refer the Greentube.Serialization repository.

Discovering and Invoking handlers

By default. Implementations of IMessageHandler<T> are discovered and registered dynamically. When classes are in assemblies other than the entry assembly or the assemblies where TMessage is defined, the library might need some help to find them. Similar to the MVC Application parts concept.

Only public implementations of IMessageHandler<T> will be automatically registered by default.

Your handlers will be created via DI. That means you can take dependencies via the constructor but mind the lifetime: The lifetime of the automatically registered Handlers is Transient. Each time a message arrives, the library will ask the container for a message handler. Something like: provider.GetService<IMessageHandler<T>>(); for each call. It's advisable you switch to Singleton lifetime in case your handlers are thread-safe.

The characteristics mentioned above can be customized with:

builder.AddHandlerDiscovery(d =>
    {
        d.IncludeNonPublic = true;
        d.DiscoveredHandlersLifetime = ServiceLifetime.Singleton;
        d.MessageHandlerAssemblies.Add(typeof(SomeMessage).Assembly);
    });

Features planned

Add Message to Topic name map via Attributes

Limitations

Currently it only supports a single Handler per Message type. You can easily work around it by implementing some composite pattern on your Handler by dispatching a call to multiple, pontentially in multiple threads, etc. We can consider adding such support if there's demand.

Greentube/messaging