How to handle unhandled exception throw in monix onErrorHandle - scala

Question

I am using monix tasks and i am trying to catch a Throwable and then convert to a custom error. I have removed/changed the code to be simple and relevant. This is the code (question follows after the code snippet):
import io.netty.handler.codec.http.HttpRequest
import monix.reactive.Observable
import io.netty.buffer.ByteBuf
import monix.eval.Task
import com.mypackage.Response
private[this] def handler(
request: HttpRequest,
body: Observable[ByteBuf]
): Task[Response] = {
val localPackage = for {
failfast <- Task.eval(1 / 0)
} yield failfast
// Failure case.
localPackage.onErrorRecoverWith {
case ex: ArithmeticException =>
print(s"LOG HERE^^^^^^^^^^^^^^^")
return Task.now(
Response(HttpResponseStatus.BAD_REQUEST,
None,
None)
)
}.runAsync
// Success case.
localPackage.map { x =>
x match {
case Right(cool) =>
Response(
HttpResponseStatus.OK,
None,
cool
)
case Left(doesntmatter) => ???
}
}
}
I am able to see the print statement but the expected Task.now(Response(... is not being returned. Instead the method that calls the handler method is throwing an error. How do i make it return the Task[Response] ?
The success case works, the failure case does not.
Edit #1 : Fix errors in scala code.
Edit #2 This is how I fixed it.
// Success case.
localPackage.map { x =>
x match {
case Right(cool) =>
Response(
HttpResponseStatus.OK,
None,
cool
)
case Left(doesntmatter) => ???
}
}.onErrorRecoverWith {
case ex: ArithmeticException =>
print(s"LOG HERE^^^^^^^^^^^^^^^")
return Task.now(
Response(HttpResponseStatus.BAD_REQUEST,
None,
None)
)
}
I was thinking in terms of future and forgot the lazy eval nature of task. Also I understood how the CancellableFuture value was being discarded in the failure task.

Answer 1

Several problems with your sample.
For one this code isn't valid Scala:
val localPackage = for {
failfast <- 1 / 0
} yield failfast
I guess you meant Task.eval(1 / 0).
Also onErrorHandle does not have a Task as a return type, you were probably thinking of onErrorHandleWith. And it's a pretty bad idea to give it a partial function (i.e. a function that can throw exceptions due to matching errors) — if you want to match on that error, then better alternatives are onErrorRecover and onErrorRecoverWith, which take partial functions as arguments.
So here's a sample:
import monix.eval._
import monix.execution.Scheduler.Implicits.global
val task = Task.eval(1 / 0).onErrorRecoverWith {
case _: ArithmeticException => Task.now(Int.MinValue)
}
task.runAsync.foreach(println)
//=> -2147483648
Hope this helps.