Custom Middleware

Definition

Middleware in JustSaying is similar to middleware in ASP.NET Core. They derive from MiddlewareBase<HandleMessageContext, bool>, and implement this method:

Task<bool> RunInnerAsync(
    HandleMessageContext context,
    Func<CancellationToken, Task<bool>> func,
    CancellationToken stoppingToken)

HandleMessageContext: A context object containing the Message, its type, and the queue it was pulled from.

Func<CancellationToken, Task<bool>>: The next middleware in the pipeline that you should call in your implementation.

CancellationToken: This is the top level CancellationToken that is passed to StartAsync - it should be checked and passed to operations that accept one so that if the bus stops, any in-progress middlewares can be cancelled.

Usage

Once you've defined a middleware, it can be added to a pipeline using the WithMiddlewareConfiguration API with the Use<TMiddleware> method. In this case, the TMiddleware will be resolved from the provided IServiceResolver.

Note that all middlewares are singletons, and will only be resolved once per pipeline.

Alternatively, you can also expose an extension method to make it more easily discoverable to users, or to parameterise it. To do this, ensure the following:

1. The namespace of the extension method is JustSaying.Messaging.Middleware, which will ensure the method appears in autocomplete for all users.

2. It is of the form public static HandlerMiddlewareBuilder UseXX(this HandlerMiddlewareBuilder builder)

   1. Essentially, its an extension method on HandlerMiddlewareBuilder, which is the builder exposed in the API. You may accept additional parameters here that can be passed to the middleware.

3. If you require services from the DI container to create or resolve the middleware, resolve them from builder.ServiceResolver.

   1. Note that you may also need to register required services into the container for them to be made available here.