Custom directive in Akka Http - scala

Question

I have some API Rest with CRUD operations.
Each entity is identified by using UUID.
For example for Create it is similar to this:
private val createProduct = post {
path("product" / Segment) { productUUID =>
Try(UUID.fromString(productUUID)) match {
case Failure(_) => // Bad request
case Success(validUuid) =>
entity(as[ProductData]) { productData =>
onComplete(addProduct(validUuid, productData)) {
case Success(_) => complete(StatusCodes.OK)
case Failure(ex) => // some code
}
}
}
}
}
Operations Read(GET), Update(PUT) and Delete(DELETE) are similar to POST:
first step is get the uuid
for PUT get the payload using entity(as[ProductData]) (not needed for GET and DELETE)
invoke some method that returns Future[Something]
What I would like to do is remove boilerplate like:
getting the UUID, validating it, returning Bad Request if it's not valid
create some directive/function for handling the future: if there's an exception just return 500 Internal Server Error, but in case of Success continue for processing the value (I think using provide directive).
I found this example (https://fmsbeekmans.com/blog/akka-http-2-creating-custom-directives.html):
def simplifiedOnComplete[T](future: Future[T])(timeout: FiniteDuration): Directive1[T] = {
Try(Await.result(future, Duration.Inf)) match {
case Success(result) => provide(result)
case Failure(error) => failWith(error)
}
}
I said, ok, there's a try in this example! Maybe I can change it for working with UUID instead of Future:
def getUUID[T]: Directive1[T] = {
path(Segment) { maybeuuid =>
Try(UUID.fromString(maybeuuid)) match {
case Success(result) => provide(result) // compilation error here
case Failure(error) => failWith(error)
}
}
}
The code does not compile with the error:
Type mismatch. Required: Route, found: Directive1[UUID]
I guess the problem is I've added path ...
How can I create a Directive to extract the valid uuid and return Bad Request if it's not valid?
And, is it possible to encapsulate in a custom directive the code that handles de future?
For example the routes defined at the top would be something like:
private val createProduct = post {
path ("product") {
extractUUID { validUUID =>
entity(as[ProductData]) { productData =>
futureSuccess(addProduct(validUUID, productData)) { successValue =>
// code here, for example: complete(OK)
}
}
}
}
}

Answer 1

You were almost there - Your code is :
def getUUID[T]: Directive1[T] = {
path(Segment) { maybeuuid =>
Try(UUID.fromString(maybeuuid)) match {
case Success(result) => provide(result) // compilation error here
case Failure(error) => failWith(error)
}
}
}
You don't need generic T since you can only have a UUID back from UUID.fromString
path(Segment) gives you a Directive. So you want to useflatMap to get a Directive back (provide returns a Directive)
So it would be something like
def getUUID: Directive1[UUID] = {
path(Segment).flatMap { maybeuuid =>
Try(UUID.fromString(maybeuuid)) match {
case Success(result) => provide(result)
case Failure(error) => failWith(error)
}
}
}
And, is it possible to encapsulate in a custom directive the code that
handles de future?
Yes, it is the same as the above. onComplete returns a Directive so you will have to flatMap.
To return BadRequest, look up the rejection handlers in the akka-http doc.