Eidetic Projector

This library aims to make it trivial to consume events, from whatever source, and run them through middleware.

Install

Everything likely to change as this is rolled out internally at GT8. Not recommended for use by anyone else; yet 😉

Consumer

Consumers are modules that subscribe to a data source and convert a payload into an Eidetic Projector Bundle. It’s the responsiblity of the consumer to prepare the payload for the Projector and to convert the response into whatever the calling consumer expects.

%Eidetic.Projector.Bundle{
    # A map storing any information that is relevant from the consumer, such as topic consumed and offset
    consumer: map(),
    # Modifiers can be set by the preprocess middleware, to provide information that may change how the handler
    # proceeds
    modifiers: map(),
    # A handler must be configured by one of the preprocess middlewares
    handler: atom() | fun(),
    # Event can be anything you want, we enforce nothing
    event: any(),
    # A map storing the result, which can be modified by middlewares and the actual handler
    result: map()
}

Middleware

Middleware should implement Eidetic.Projector.Middleware, which describes what to expect:

@callback process(%Bundle{}) :: {:ok | :skip | :error, %Bundle{}}

The first element of the return tuple from the middleware instructs the projector how to proceed:

:ok means we’re happy. Continue to call all other middleware and our handler :skip means we do not wish to handle this bundle and should exit, without calling any other middleware, or the handler :error means we experienced a problem handling this bundle and we should retry again soon. No other middleware, or the handler, is called.

It doesn’t make a lot of sense for a postprocess handler to return anything other than an :ok tuple. We may disregard responses from postprocess handlers, but that isn’t the case yet.

Handler

There is no handler that can be configured up-front or globally. You MUST use the preprocess middleware to configure a handler on the %Bundle{handler: handler} struct.

The handler can be set to an atom, which will assume it’s a module and call handle/1. The handler may also be a function.

The handler should also respect the middleware callback:

@callback process(%Bundle{}) :: {:ok | :skip | :error, %Bundle{}}

Shit I Don’t Need

Yes, you’ll find some Consumers, Handlers and Middleware in this repository that you don’t need. As I said, you shouldn’t be using it. These are here until we’re stabilised the API; after which we’ll remove them. I wonder if anyone will ever read this anyway 👀

If you do, drop us an email!

developers@gt8.online