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!

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

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

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

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
    }
}

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" }
                }
            }
       }
}

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
}

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

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

Thank you, i'll explore that option

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

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