Is there a good way to scope an `Application.confi...

# ktor

[bbaldino]

Is there a good way to scope an Application.configureRoutes()-type method within a class to be able to add additional context? For example, I want to be able to fire events when a new websocket is established, so want a way to store a sort of ‘event emitter’, and therefore allow external entities to be able to subscribe to those events. I think maybe the new Context Receivers would handle this? But looking for another way since those are still experimental.

[bbaldino]

For example:

class MyClass {
    private val eventHandlers = mutableListOf<EventHandler>()

    fun addEventHandler(handler: EventHandler) {
        eventHandlers += handler
    }

    fun Application.configureRoutes() {
        webSocket("/ws") {
            eventHandlers.forEach { it.websocketConnected() }
            ...
        }
    }
}

[Landry Norris]

Does making MyClass an object work? I believe you can import extension functions that are members of an object. Alternatively, you could make the Application a parameter.

[bbaldino]

Making the context a parameter to the function was my plan for a fallback…I haven’t tried an object. I’m hoping for a class, though, because generally I find that easier for things like testing, but admittedly I haven’t used plain objects much for something like this.

[Joost Klitsie]

I think it makes sense to not have the MyClass wrap the eventHandlers and the routing, as part of a separation of concerns. You can of course do that and it will look like:

fun Application.module() {
    val myClass = MyClass()
    with(myClass) {
        configureRoutes()
    }
}

[Joost Klitsie]

But I think it is better to pass in the myClass object as a parameter (sort of a dependency) to configureRouts

[Joost Klitsie]

fun Application.module() {
    val myClass = MyClass()
    configureWebSockets(myClass)
}

fun Application.configureWebSockets(myClass: MyClass) {
    webSocket("/ws") {
        myClass.onWebSocketConnected() // <-- do something there within your myClass
    }
}

[Joost Klitsie]

to be fair it may depend on the usecase 😄

[Joost Klitsie]

I have a project where I instantiate backend services and they indeed have an fun Application.installRouting() in these service classes