Anyone knows how the top-level `fold` handles `TimeoutCancellationException` s? It seems like they'...

# arrow

[dave08]

Anyone knows how the top-level fold handles TimeoutCancellationException s? It seems like they're rethrown... but in Ktor, I'd like to use it to return some kind of timeout response to the client... (I suspect that Ktor just hangs w/o some kind of timeout in certain situations...)

[dave08]

Would this do it:

private suspend inline fun KtorCtx.respond(
    statusCode: HttpStatusCode,
    noinline action: suspend Raise<ErrorContext>.() -> String
): Unit = fold(
    {
        withTimeout(5.seconds) {
            action()
        }
    },
    { 
        if (it is TimeoutCancellationException)
            call.respond(RequestTimeout)
        else
            throw it
    },
    { error ->
        val jsonError = Json.encodeToString(error)
        call.respond(BadRequest, error.toString())
        application.log.error(jsonError)
    }) { a ->
        call.respondText(a, ContentType.Application.Json, statusCode)
    }

[dave08]

?

[stojan]

you could use withTimeoutOrNull

[dave08]

... not such a nice hack there with ?: ""

private suspend inline fun KtorCtx.respond(
    statusCode: HttpStatusCode,
    noinline action: suspend Raise<ErrorContext>.() -> String
): Unit = fold(
    {
        withTimeoutOrNull(5.seconds) {
            action()
        }?.also { call.respond(RequestTimeout) } ?: ""
    },
    { error ->
        val jsonError = Json.encodeToString(error)
        call.respond(BadRequest, error.toString())
        application.log.error(jsonError)
    }) { a ->
        call.respondText(a, ContentType.Application.Json, statusCode)
    }

[dave08]

Otherwise a isn't a type respondText accepts...

[simon.vergauwen]

This is because TimeoutCancellation inherits from CancellationException. There is some discussion on KotlinX Coroutines to change this, but it’s a binar breaking change.

They might change this is 2.0, but you can use withTimeoutOrNull & custom exception or Java’s TimeoutException