Handle services returning Try values in Spray - scala

Question

I am working on a codebase where calling my Spray API need to synchronously call a service that returns a Try which Spray need to format and return over HTTP.
My initial attempt looked like this :
// Assume myService has a run method that returns a Try[Unit]
lazy val myService = new Service()
val routes =
path("api") {
get {
tryToComplete {
myService.run()
}
}
} ~
path("api" / LongNumber) { (num: Long) =>
get {
tryToComplete {
myService.run(num)
}
}
}
def tryToComplete(result: => Try[Unit]): routing.Route = result match {
case Failure(t) => complete(StatusCodes.BadRequest, t.getMessage)
case Success(_) => complete("success")
}
However this caused myService.run() to be called when the application started. I am not sure why this method was called as there was no HTTP call made.
So I have two questions :
Why is my service being called as part of initialising the routes?
What is the cleanest way to handle this case? Imagine that there are a few other end points following a similar pattern. So I need to be able to handle this consistently.

Answer 1

Even though you have result parameter as call-by-name, it'll immediately get evaluated as you're doing
result match {
For it not to get evaluated, it has to be within the complete, ie your code should look something like (haven't tried to compile this):
def tryToComplete(result: => Try[Unit]): routing.Route = complete {
result match {
case Failure(t) => StatusCodes.BadRequest, t.getMessage
case Success(_) => "success"
}
}

Answer 2

The way I solved this was do do the following :
lazy val myService = new Service()
val routes =
path("api") {
get {
complete {
handleTry {
myService.run()
}
}
}
} ~
path("api" / LongNumber) { (num: Long) =>
get {
complete {
handleTry {
myService.run(num)
}
}
}
}
private def handleTry(operation: Try[_]):HttpResponse = operation match {
case Failure(t) =>
HttpResponse(status = StatusCodes.BadRequest, entity = t.getMessage)
case Success(_) =>
HttpResponse(status = StatusCodes.OK, entity = successMessage)
}