Hi guys, I've been looking for this info in the in...

# ktor

[Carlos Santos]

Hi guys,
I've been looking for this info in the internet but I couldn't find a clear answer.
Let's say that I have an endpoint like: GET -> /ktor
I want to create an interceptor and put it in the pipeline but only for that particular endpoint. I don't want to create an interceptor and then check the request path like in the docs. I was looking for "clean" solution like a plugin or something similar. I know that there's an interface named RootRouteSelector but I couldn't figured out how it works.
Do you know if this is possible, and if so, can you point me to some docs/example.
Thank you!

[Aleksei Tirman [JB]]

Could you please describe what do you want to achieve and why a route handler is insufficient?

[Carlos Santos]

I want to intercept a request, get the parameters, call a second service to validate one of those parameters, save the response of the second service in cache and if everything is ok, proceed

[Carlos Santos]

i dont want to put this logic in the inside the route, cuz i will have multiple routes that will need this validation

[Joost Klitsie]

I think you should be able to write a feature for this

[Joost Klitsie]

that wraps around your route

[Aleksei Tirman [JB]]

You can write an extension function for a Route and in its body, create a new route with a custom selector. In that selector, you may have a validation logic. Here is an example:

fun main() {
    embeddedServer(Netty, port = 8080) {
        routing {
            validate {
                get("/") {
                    call.respondText { "ewqe" }
                }
            }
        }
    }.start(wait = true)
}

fun Route.validate(validator: MyValidator = MyValidator(), build: Route.() -> Unit): Route {
    val newRoute = createChild(MySelector(validator))
    newRoute.build()
    return newRoute
}

class MySelector(private val validator: MyValidator): RouteSelector() {
    override fun evaluate(context: RoutingResolveContext, segmentIndex: Int): RouteSelectorEvaluation {
        if (validator.validate()) {
            return RouteSelectorEvaluation.Constant
        }

        return RouteSelectorEvaluation.Failed
    }
}

class MyValidator {
    fun validate(): Boolean {
        return true
    }
}

[Carlos Santos]

Got your idea, just one more question. How can i be sure that this will always run after authenticate?
Would that be like?:

...
routing {
    authenticate(...){
            validate {
                get("/") {
                    call.respondText { "ewqe" }
                }
            }
       }
}

[Rustam Siniukov]

While solution from @Aleksei Tirman [JB] will work, it’s better to use interceptors instead of putting logic to evaluate . Something like

fun Route.validate(validator: MyValidator = MyValidator(), build: Route.() -> Unit): Route {
    val newRoute = createChild(MySelector())
    newRoute.intercept(Call) { validator() }
    return newRoute
}

[Carlos Santos]

How can i make the intercept run after authenticate? I need to make it run after the authenticate and before the request being handled.
That interceptor and the authenticate both run in the same fase, and i need to make it run after the call being authenticated

[Carlos Santos]

I could also run this while the request is being authenticated, but we have no access to the request in that context

[Rustam Siniukov]

Routing keeps order of interceptors. Your interceptor should be invoked after any interceptors from parent routes, including authentication

[Carlos Santos]

Thank you, i'll explore that option

[Carlos Santos]

...
routing {
    authenticate(...){
            validate {
                get("/") {
                    call.respondText { "ewqe" }
                }
            }
       }
}

...
fun Route.validate(validator : Validator, build: Route.() -> Unit): Route {

    val newRoute = createChild(MySelector(1.0))
    newRoute.intercept(ApplicationCallPipeline.Features) {
        doSomething
    }
    newRoute.build()
    return newRoute
}

If i do this, it will run the intercep 1st and only after it will run the authentication

[Rustam Siniukov]

Oh, sorry, you are right. I forgot that Authentication adds it’s own phase.
You need a bit more code to make it work.

private val validationPhase = PipelinePhase("Validate")

fun Route.validate(validator : Validator, build: Route.() -> Unit): Route {
    val newRoute = createChild(MySelector())
    newRoute.insertPhaseAfter(ApplicationCallPipeline.Features, Authentication.ChallengePhase)
    newRoute.insertPhaseAfter(Authentication.ChallengePhase, validationPhase)
    newRoute.intercept(validationPhase) {
        doSomething
    }
    newRoute.build()
    return newRoute
}

class ValidationSelector: RouteSelector() {
  fun evaluate(context: RoutingResolveContext, segmentIndex: Int) = RouteSelectorEvaluation.Transparent
}

This way you make sure that your phase for validation will be after authentication phases.
It’s a bit complicated and you need to know the internals of how phases work, that’s why we will implement simpler API in 2.0.0. You can follow it here https://youtrack.jetbrains.com/issue/KTOR-929

[Carlos Santos]

it works,
Thank you Rustam, it was really helpful! 👍