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#ktor
Title
# ktor
c

Carlos Santos

07/23/2021, 8:21 AM
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!
👍 1
a

Aleksei Tirman [JB]

07/23/2021, 8:55 AM
Could you please describe what do you want to achieve and why a route handler is insufficient?
c

Carlos Santos

07/23/2021, 9:06 AM
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 dont want to put this logic in the inside the route, cuz i will have multiple routes that will need this validation
j

Joost Klitsie

07/23/2021, 12:11 PM
I think you should be able to write a feature for this
that wraps around your route
a

Aleksei Tirman [JB]

07/23/2021, 12:26 PM
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:
Copy code
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
    }
}
c

Carlos Santos

07/23/2021, 1:07 PM
Got your idea, just one more question. How can i be sure that this will always run after authenticate? Would that be like?:
Copy code
...
routing {
    authenticate(...){
            validate {
                get("/") {
                    call.respondText { "ewqe" }
                }
            }
       }
}
r

Rustam Siniukov

07/23/2021, 1:47 PM
While solution from @Aleksei Tirman [JB] will work, it’s better to use interceptors instead of putting logic to
evaluate
. Something like
Copy code
fun Route.validate(validator: MyValidator = MyValidator(), build: Route.() -> Unit): Route {
    val newRoute = createChild(MySelector())
    newRoute.intercept(Call) { validator() }
    return newRoute
}
c

Carlos Santos

07/23/2021, 2:24 PM
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
I could also run this while the request is being authenticated, but we have no access to the request in that context
r

Rustam Siniukov

07/23/2021, 2:34 PM
Routing keeps order of interceptors. Your interceptor should be invoked after any interceptors from parent routes, including authentication
c

Carlos Santos

07/23/2021, 2:36 PM
Thank you, i'll explore that option
Copy code
...
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
r

Rustam Siniukov

07/23/2021, 2:58 PM
Oh, sorry, you are right. I forgot that
Authentication
adds it’s own phase. You need a bit more code to make it work.
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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
1
c

Carlos Santos

07/23/2021, 3:08 PM
it works, Thank you Rustam, it was really helpful! 👍
👍 1
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