Demonstration of interceptors and call.attributes for Ktor

Routing.kt

fun Routing.targetRouting() {
  data class Target(val name: String)

  val targetKey = AttributeKey<Target>("TargetKey")

  suspend fun resolveTarget(target: String): Target? {
    delay(100)
    return Target(name = target)
  }

  data class Property(val name: String)

  val propertyKey = AttributeKey<Property>("PropertyKey")

  suspend fun resolveProperty(property: String): Property? {
    delay(200)
    return Property(name = property)
  }

  route("{target}") {
    intercept(ApplicationCallPipeline.Call) {
      call.parameters["target"]?.let { resolveTarget(it) }?.also { call.attributes.put(targetKey, it) }
          ?: throw Exception("Target cannot be resolved") //will be handled by status pages
    }
    route("{property}") {
      intercept(ApplicationCallPipeline.Call) {
        call.parameters["property"]?.let { resolveProperty(it) }?.also { call.attributes.put(propertyKey, it) }
            ?: throw Exception("Property cannot be resolved") //will be handled by status pages
      }
      get("get") {
        val resolvedTarget = call.attributes[targetKey].also { println(it) }
        val resolvedProperty = call.attributes[propertyKey].also { println(it) }
        //do your stuff
        call.respondText("Works")
      }
    }
  }
}