Akka Http return 404 Not Found

Question

I'm trying to achieve very simple thing.

Say, I have a REST API. When I call

/api/recipe/1

I'd like to a resource as a json to be returned.

When I hit

/api/recipe/2

a 404 Not Found HTTP response should be returned. Simple as that.

Clearly I'm missing something about how routing directives work, as I'm not able to compose them to respect above-mentioned logic.

Unfortunately I was unable to find any concrete example and official documentation isn't particularly helpful.

I'm trying something like this but the code gives compilation error:

class RecipeResource(recipeService: RecipeService)(implicit executionContext: ExecutionContext) extends DefaultJsonProtocol {

  implicit val recipeFormat = jsonFormat1(Recipe.apply)

  val routes = pathPrefix("recipe") {
    (get & path(LongNumber)) { id =>
      complete {
        recipeService.getRecipeById(id).map {
          case Some(recipe) => ToResponseMarshallable(recipe)
          // type mismatch here, akka.http.scaladsl.marshalling.ToResponseMarshallable 
          // is required
          case None => HttpResponse(StatusCodes.NotFound)
        }
      }
    }
  }
}

Update

Here's the code of recipeService for greater clarity:

class RecipeService(implicit executionContext: ExecutionContext) {

  def getRecipeById(id: Long): Future[Option[Recipe]] = {
    id match {
      case 1 => Future.successful(Some(Recipe("Imperial IPA")))
      case _ => Future.successful(None)
    }
  }
}

The compilation error I get:

[error] /h......../....../...../RecipeResource.scala:22: type mismatch;
[error]  found   : scala.concurrent.Future[Object]
[error]  required: akka.http.scaladsl.marshalling.ToResponseMarshallable
[error]         recipeService.getRecipeById(id).map {
[error]                                             ^
[error] one error found
[error] (compile:compileIncremental) Compilation failed

Update 2

Based on leachbj's answer I got rid of needless pattern matching in the route. Now the code compiles and looks like this:

class RecipeResource(recipeService: RecipeService)(implicit executionContext: ExecutionContext) extends DefaultJsonProtocol {

  implicit val recipeFormat = jsonFormat1(Recipe.apply)

  val routes = pathPrefix("recipe") {
    (get & path(LongNumber)) { id =>
      complete(recipeService.getRecipeById(id))
    }
  }
}

When the recipe exists (e.g. /api/recipe/1) I get the JSON response and 200 OK, which is expected.

Now, in case of the non-existent resource (e.g. /api/recipe/2) the response in empty, but 200 OK status code is received.

My question is, how can I tweak akka-http to be able to complete(Future[None[T]]) that would return 404 Not found.

I'm looking for a generic approach that would work for any Future[None] return value.

Answer 1

If you complete(Future[Option[T]]) and there is a suitable Json Marshaller available the Akka will return the response as json if the value is Some(v) or an empty 200 response for None. If you use spray-json create a RootJsonFormat[T] implicit and add import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport._. There are similar support implicits for other marshalling libraries.

To generate a 404 for None you need to wrap the complete with the rejectEmptyResponse directive.