Clacks.NET

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Clacks.NET is a .net outbox library. I'd intended this to include an inbox solution as well, but did not have a use-case for it, so figured I'd just release the outbox part. If you want to contribute an inbox solution, please do so.

Additionally, this is intended to support multiple databases; however, I am using it with postgres, so that's the only one I have tested/fleshed out. Again, if you would like to add this support, I would be happy to accept a PR.

This library does not support a dead letter queue. It will retry messages infinitely, though it will retry other messages first so the system doesn't get stuck retrying the same failed message. I intend to add a dead letter queue in the future (but would welcome if someone else wants to do this).

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Using Clacks.NET

Install the NuGet package(s)

The main package is SlySoft.Clacks.NET, which contains the core functionality. If you are using Postgres, you can also install the SlySoft.Clacks.NET.Postgres package, which contains the Postgres-specific functionality.

dotnet add package SlySoft.Clacks.NET
dotnet add package SlySoft.Clacks.NET.Postgres

Configure the Outbox via dependency injection

Call AddClacksOut in your Startup.cs or Program.cs file to register the outbox service. This method allows the setup of some configuration values, and you MUST configure a lambda expression to create a connection. In the example below, IDbConnection is registered in the DI container, and the lambda expression returns it. You may resolve the connection however you like, but it must be configured for the outbox to work.

Note: the connection must have the permission to run DDL commands, as the outbox will create the table if it does not exist.

using SlySoft.ClacksNet;

...

services.AddClacksOut(x => 
{
    x.GetConnection = services => services.GetRequiredService<IDbConnection>();
});

Sending messages to the outbox

This will allow you to write to the outbox by injecting IClacksOut into your classes. You can call the Send method with a topic and a message. These values will be available when the outbox is processed later on. Note that there is both a synchronous and asynchronous version of the Send method.

using SlySoft.ClacksNet;

public class MyService(IClacksOut clacksOut)
{
    public async Task DoSomething()
    {
        var subject = "messages.to-the-world";
        var message = "Hello, World!"
        await clacksOut.SendAsync(subject, message);
    }
}

Processing the outbox

To process the outbox, you must provide an implementation of the IClacksOutSender interface. This interface contains one method, SendAsync, which is called when the outbox is processed (by default, polled once per minute, though this value is configurable). You must return true if the message was sent successfully. Note that message contains a unique ID, which you should use to perform idempotency checks.

using SlySoft.ClacksNet;

internal sealed class OutboxSender : IClacksOutSender {
    public Task<bool> SendMessage(ClacksOutMessage message, CancellationToken cancellationToken = default) {
        Console.WriteLine($"Sending message: {message.Topic} - {message.Message}");
        return Task.FromResult(true);
    }
}

You do not need to register this class with the DI container, but you DO need to provide it as a configuration value when calling AddClacksOut. See the following example:

using SlySoft.ClacksNet;

...

services.AddClacksOut(x => 
{
    x.GetConnection = services => services.GetRequiredService<IDbConnection>();
    x.Sender = typeof(OutboxSender);
    x.PollingInterval = TimeSpan.FromSeconds(10);
});

Additionally, if you are using Postgres, you can add a reference to the SlySoft.ClacksNet.Postgres package, and add the AddPostgresClacksOutListener method to your DI container. This will create a listener for the outbox table that triggers on inserts. This will augment the polling and allow for more immediate processing of messages.

services.AddClacksOut(x => 
{
    x.GetConnection = services => services.GetRequiredService<IDbConnection>();
    x.Sender = typeof(OutboxSender);
    x.PollingInterval = TimeSpan.FromSeconds(10);
})
.AddPostgresClacksOutListener();