README.md

Remora.Discord.Gateway

This package provides a fully-featured implementation of a Discord gateway client, complete with resume capabilities and user-facing events.

Structure

The package consists of two main parts - the client itself, and the event dispatch system. The latter will be familiar to users of the mediator pattern, wherein an intermediate type handles communication between separate objects; in Remora.Discord.Gateway's case, all incoming Discord events are dispatched and executed concurrently with each other, and the user may register responders to handle these events.

Provided you yourself do not inject services with a shared mutable state, all responders are thread-safe and do not require additional synchronization through semaphores or mutexes.

The client is a singleton service by design.

Usage

First and foremost, the gateway client must be registered with your dependency injection container.

services.AddDiscordGateway(serviceProvider => GetTokenFromSomewhere(serviceProvider));

Two things to note:

• You are not required to call any other methods from dependency libraries (such as Remora.Discord.API) - this call takes care of all transitive dependencies itself.
• You must, at this point, provide a way to access your bot's token in plain text. This access only happens after the container is constructed, and an API instance is requested, so you have access to the built container.

After this point, you may inject the gateway client into your own services. In order to connect and start dispatching events, you must call RunAsync somewhere, and subsequently either await the task directly or store it for later use. This task represents the entire lifetime of the gateway client, and will run until you explicitly request its termination via the cancellation token passed to this method.

If you wish to explicitly send a gateway command (for example, to update presence information), you may do so via the SubmitCommand method on the client. Note that no validations are performed on this command, so you can cause unexpected termination of your session if the data is malformed or inappropriate for the current state of the client.

Responders - the types which react to and handle incoming events - are created by declaring a class that implements one or more instances of the IResponder<T> interface, and then registering these types with the service container.

public class MyResponder : IResponder<IMessageCreate>
{
    public async Task<Result> RespondAsync
    (
        IMessageCreate gatewayEvent,
        CancellationToken ct = default
    )
    {
        // ...
    }
}

...

services.AddResponder<MyResponder>();

There are no restrictions placed on how long an individual responder may run, but you should strive to keep it short in order to avoid thread pool exhaustion.

Responders have no guarantees related to sequential execution, but you are able to sort them into one of three "groups", which do run sequentially to one another.

services.AddResponder<MyResponder>(ResponderGroup.Early); // executes before...
services.AddResponder<MyResponder>(ResponderGroup.Normal); // executes before...
services.AddResponder<MyResponder>(ResponderGroup.Late);

This is useful in cases where two responders to the same event depend on each other in some way.