Ktor Routing

Parent context: See root AGENTS.md (lines 147-167) for error handling and routing rules. This skill provides concrete code examples that complement those rules. The codebase uses Ktor only -- no annotation-based web frameworks.

When to use me

• Trigger: building a new REST endpoint or fun Route.X() extension
• Trigger: wiring a new app's Application.<appName>() module
• Trigger: handling errors via StatusPages and ApiError
• Trigger: adding authenticate("name") { ... } JWT blocks
• Trigger: throwing badRequest(), notFound(), conflict(), etc. from a route handler

Route as extension function

Routes are defined as extension functions on Route. Dependencies are passed as constructor-style parameters. No annotations, no DI framework.

// Source: apps/utsjekk/main/utsjekk/routes/IverksettingRoute.kt:16-30
fun Route.iverksetting(
    service: IverksettingService,
    migrator: IverksettingMigrator,
) {
    route("/api/iverksetting") {

        post("/v2/migrate") {
            val fagsystem = call.fagsystem()
            val request = call.receive<MigrationRequest>()
            if(request.meldeperiode == null && request.uidToStønad == null) badRequest("mangler en av: 'meldeperiode' eller 'uidToStønad'")
            if (request.meldeperiode != null && request.uidToStønad != null) badRequest("mutual exclusive: 'meldeperiode' and 'uidToStønad'")
            val utbetalinger = migrator.mapUtbetalinger(fagsystem, request)
            utbetalinger.forEach { migrator.migrate(request, it) }
            call.respond(HttpStatusCode.OK)
        }
    }
}

Path parameters use call.parameters.getOrFail<String>("name") and are wrapped into value classes via .let(::SakId):

// Source: apps/utsjekk/main/utsjekk/routes/IverksettingRoute.kt:65-73
get("/{sakId}/{behandlingId}/status") {
    val sakId = call.parameters.getOrFail<String>("sakId").let(::SakId)
    val behandlingId = call.parameters.getOrFail<String>("behandlingId").let(::BehandlingId)
    val fagsystem = call.fagsystem()
    val status = service.utledStatus(fagsystem, sakId, behandlingId, null)
        ?: notFound("Fant ikke status utbetaling med sakId $sakId og behandlingId $behandlingId")

    call.respond(HttpStatusCode.OK, status)
}

Application wiring

The app's module function (fun Application.<appName>()) takes dependencies as parameters with sensible defaults, manually wires services, and installs Ktor plugins. The routing { ... } block at the bottom registers all Route extensions.

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:73-78
fun Application.utsjekk(
    config: Config = Config(),
    kafka: Streams = KafkaStreams(),
    jdbcCtx: CoroutineDatasource = Jdbc.initialize(config.jdbc).context(),
    topology: Topology = createTopology(jdbcCtx),
) {

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:163-174
routing {
    authenticate(TokenProvider.AZURE) {
        iverksetting(iverksettingService, iverksettingMigrator)
        utbetalinger(utbetalingService, utbetalingMigrator)
        simuleringRoutes.aap(this)
        simuleringRoutes.utsjekk(this)
        simuleringRoutes.abetal(this)
        simuleringRoutes.dryrun(this)
    }

    actuator(kafka, metrics)
}

main() calls embeddedServer(...).start(wait = true) referencing the module function:

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:60-71
embeddedServer(
    factory = Netty,
    configure = {
        shutdownGracePeriod = 5000L
        shutdownTimeout = 50_000L
        connectors.add(EngineConnectorBuilder().apply {
            port = 8080
        })
    },
    module = Application::utsjekk,
).start(wait = true)

StatusPages + ApiError

StatusPages is installed once per app and centralizes exception → HTTP mapping. ApiError becomes the response body verbatim; everything else maps to 400 (parse error) or 500.

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:97-116
install(StatusPages) {
    exception<Throwable> { call, cause ->
        when (cause) {
            is ApiError -> call.respond(HttpStatusCode.fromValue(cause.statusCode), cause)
            is BadRequestException -> {
                val msg = "Klarte ikke lese json meldingen. Sjekk at formatet på meldingen din er korrekt, f.eks navn på felter, påkrevde felter, e.l."
                appLog.debug(msg)
                secureLog.debug(msg, cause)
                val res = ApiError(statusCode = 400, msg = msg)
                call.respond(HttpStatusCode.BadRequest, res)
            }
            else -> {
                val msg = "Ukjent feil, helved er varslet."
                appLog.error(msg, cause)
                val res = ApiError(statusCode = 500, msg = msg)
                call.respond(HttpStatusCode.InternalServerError, res)
            }
        }
    }
}

ApiError is a RuntimeException data class with statusCode, msg, doc, and system. Default doc points to DocumentedErrors.BASE; default system is System.HELVED.

// Source: models/main/models/ApiError.kt:105-110
data class ApiError(
    val statusCode: Int,
    val msg: String,
    val doc: String? = DocumentedErrors.BASE,
    val system: System? = System.HELVED,
) : RuntimeException(msg) {

Helper functions

All helpers return Nothing so they can be used inside expressions (Elvis, if-else) without breaking type inference. They throw ApiError with the appropriate HTTP status code; StatusPages does the rest.

// Source: models/main/models/ApiError.kt:124-145
fun badRequest(msg: String, doc: String? = null): Nothing = throw ApiError(400, msg, doc ?: DocumentedErrors.BASE)
fun badRequest(error: DocumentedErrors.Async): Nothing = throw ApiError(400, error.msg, error.doc)

fun forbidden(msg: String, doc: String? = null): Nothing = throw ApiError(403, msg, doc ?: DocumentedErrors.BASE)

fun notFound(msg: String, doc: String? = null): Nothing = throw ApiError(404, msg, doc ?: DocumentedErrors.BASE)
fun notFound(error: DocumentedErrors.Async): Nothing = throw ApiError(404, error.msg, error.doc)

fun conflict(msg: String, doc: String? = null): Nothing = throw ApiError(409, msg, doc ?: DocumentedErrors.BASE)
fun conflict(error: DocumentedErrors.Async): Nothing = throw ApiError(409, error.msg, error.doc)

fun unprocessable(msg: String, doc: String? = null): Nothing = throw ApiError(422, msg, doc ?: DocumentedErrors.BASE)
fun locked(msg: String, doc: String? = null): Nothing = throw ApiError(423, msg, doc ?: DocumentedErrors.BASE)
fun internalServerError(msg: String, doc: String? = null): Nothing =
    throw ApiError(500, msg, doc ?: DocumentedErrors.BASE)

fun notImplemented(msg: String, doc: String? = null): Nothing = throw ApiError(501, msg, doc ?: DocumentedErrors.BASE)
fun badGateway(msg: String, doc: String? = null): Nothing = throw ApiError(502, msg, doc ?: DocumentedErrors.BASE)

fun unavailable(msg: String, doc: String? = null): Nothing = throw ApiError(503, msg, doc ?: DocumentedErrors.BASE)

fun unauthorized(msg: String): Nothing = throw ApiError(

Use them inline with Elvis on nullable lookups, in validation guards, or in when branches:

// Source: apps/utsjekk/main/utsjekk/routes/IverksettingRoute.kt:69-70
val status = service.utledStatus(fagsystem, sakId, behandlingId, null)
    ?: notFound("Fant ikke status utbetaling med sakId $sakId og behandlingId $behandlingId")

For domain errors with documentation links, prefer the DocumentedErrors.Async overload over a free-text message.

Authentication

JWT auth providers are installed in Authentication, then routes are wrapped in authenticate("provider-name") { ... }. Unauthenticated routes (e.g. actuator) sit outside the block.

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:92-96
install(Authentication) {
    jwt(TokenProvider.AZURE) {
        configure(config.azure)
    }
}

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:163-174
routing {
    authenticate(TokenProvider.AZURE) {
        iverksetting(iverksettingService, iverksettingMigrator)
        utbetalinger(utbetalingService, utbetalingMigrator)
        simuleringRoutes.aap(this)
        simuleringRoutes.utsjekk(this)
        simuleringRoutes.abetal(this)
        simuleringRoutes.dryrun(this)
    }

    actuator(kafka, metrics)
}

JWT claims are read off the JWTPrincipal inside handlers. Throw forbidden() / unauthorized() when claims are missing:

// Source: apps/utsjekk/main/utsjekk/Utsjekk.kt:184-190
fun ApplicationCall.client(): Client =
    principal<JWTPrincipal>()
        ?.getClaim("azp_name", String::class)
        ?.split(":")
        ?.last()
        ?.let(::Client)
        ?: forbidden("missing JWT claim")

Cross-references

• For Ktor library API (HttpClientFactory, CallLog, TokenValidator, KtorRuntime), load the libs-reference skill.
• For Ktor test setup (KtorRuntime, runTest, JWT generation), load the testing skill.
• Root AGENTS.md lines 147-167 define error handling and DI rules — do not duplicate.
• For Norwegian domain terms (Iverksetting, Utbetaling, Sak, Fagsystem), see apps/AGENTS.md.