About tone, I am very matter of fact and blunt. Its not intended to offend,
just be more efficient. Sorry if you took it badly.
Ok I reviewed the artilce, In fact I thought i had linked that one. It
still leaves a lot of information in the route itself and is still rather
simplistic. For example consider the path:
pathPrefix("order" / IntNumber) { orderId =>
In this path the implementer assumes the order number is valid, that the
user has access to the order, that the order is not blocked according to
HAZMAT and DHS regulations from being seen by the user in question and a
thousand other examples of problems that could arrise. It just assumes the
order is visible. Now if I want to do all of that checking I have to do it
in a route because if they give a bad order number I need to route to a bad
request, if they try to alter an order they dont have permissions to alter,
I have to route to a forbidden, if the order is blocked by DHS regulations
from being viewed outside secret channels I have to log the unauthorized
attempt, and then route to bad request or fobidden and if the database goes
down I have to route to internal error.
Now down we put all of that logic in the route? It might not even be
possible, the logic could be a result of aggregating data together from
several other actors and maybe even extra network calls. See where I am
going with this? Once we fork off to the actor we have lost the route, we
cant get it back to make decisions based on the data in the system. The
only way those decisions on the different outcomes can be made is in the
actor handling the request. One alternative is to create an intermediary
model to be interpreted back in the route but that is introducing a lot of
code for what I would consider nominal gain and a potential maintenance
nightmare given I might have 300 endpoints.
See where I am going with this?
Now alternatively if I could pass some kind of context to the actor, the
actor could take care of all of that heavy lifting and simply resume the
route when it determined the fate of the request. That would make the
system massively easier to use and I think would avoid what I personally
see as an anti-pattern.
On Monday, April 3, 2017 at 10:52:05 AM UTC-5, Ryan Tanner wrote:
>
> Leaving aside the tone of this post...
>
> Have you looked at the longer example of the DSL?
>
>
> http://doc.akka.io/docs/akka-http/current/scala/http/routing-dsl/index.html#longer-example
>
> It has examples of how to delegate an endpoint's business logic off to
> actors or futures.
>
> On Sunday, April 2, 2017 at 7:09:32 PM UTC-6, kraythe wrote:
>>
>> I was really excited about akka-http as I would be able to unburden my
>> code from the baggage of play and handle my server side as a pure akka
>> actors app but unless I am much mistaken something is dreadfully amiss with
>> the implementation.
>>
>> One of the main core features is the actor paradigm and the integration
>> of a rich actor system. However, the preferred approach to akka-http seems
>> to be a throwback to one file programming. The main reason it seems this
>> way is the DSL. Take this example from a tutorial:
>>
>> path("bank" / IntNumber) { id =>
>> get {
>> complete {
>> getById(id).map{result =>
>> if(result.isDefined)
>> HttpResponse(entity =write(result.get))
>> else
>> HttpResponse(entity ="This bank does not exist")
>> }
>>
>>
>> }
>> }
>> }~
>> path("bank" / "update") {
>> post {
>> entity(as[String]) { bankJson =>
>> complete {
>> val bank =parse(bankJson).extract[Bank]
>> update(bank).map{result => HttpResponse(entity ="Bank
>> has been updated successfully")}
>> }
>> }
>> }
>> }
>> }
>> }
>>
>>
>> Simple enough right? Too me I see the start of an anti-pattern but lets
>> look further. It gets worse though, quickly, as shown in the akka-http
>> documentation here
>> <http://doc.akka.io/docs/akka-http/10.0.0/scala/http/routing-dsl/index.html#longer-example>.
>>
>> Still not bothered? The problem is that these examples are shallow and not
>> rooted in the real world. In the bank application above would be hundreds
>> of endpoints and each endpoint would have to validate data send by the
>> user, check to see whether that data correct against the database and a
>> dozen other things that would alter the nature of the return type to a bad
>> request or internal error. The banking app would also have to log the
>> problems so forensics can be done on malicious users. Just taking one route
>> "deposit" would be several hundred lines of code INSIDE the route. However,
>> it seems that there is no way to break off the route, offload it to another
>> component (such as a Per Request Actor) and then continue the DSL where you
>> left off. I had the chance to see for an app in another company that was
>> asking my advice and their route is 12k lines long and at one point nested
>> 30 levels deep.
>>
>> Now I know what you might say, "But Robert, you can break up the route
>> into multiple files" which is true but something has to manually
>> concatenate all of those routes together and they cant be done off of the
>> main route. once you are in the routes DSL you are stuck there. Sure, you
>> can call an actor with a future to do a completion but that actor itself
>> might return data that requires a different kind of completion based upon
>> certain criteria such as whether the user has had their account suspended.
>> So if your completions are diverse, how do you break up the route?
>>
>> Now if someone has answers to these issues I would love to hear them but
>> after researching I found that basically PRA's are deprecated in favor of a
>> "convenient" DSL that entraps the user. For my purposes I opted to go with
>> the low level API and factor off the route dispatching to a routing actor
>> (yes, I know this is what the materializer does) and then just pull out
>> route data the old fashioned way. My router, does path checking and then
>> dispatches to another actor to handle that specific request and then sends
>> the HttpResponse entity back to the sender which completes the ask and the
>> route. My startup looks like this:
>>
>> val serverSource: Source[Http.IncomingConnection, Future[Http.
>> ServerBinding]] =
>> Http().bind(interface = "localhost", port = 8080)
>> log.info("Server online at http://localhost:8080";)
>> val bindingFuture: Future[Http.ServerBinding] =
>> serverSource.to(Sink.foreach { connection => // foreach materializes
>> the source
>> import akka.pattern.ask
>> println("Accepted new connection from " + connection.remoteAddress)
>> connection.handleWithAsyncHandler(request => (httpRouter ? request
>> ).mapTo[HttpResponse], parallelism = 4)
>> }).run()
>>
>>
>> A snippet of the router looks like this.
>>
>> class HttpRequestRouter extends Actor {
>> protected val log = Logging(context.system, this)
>>
>>
>> override def receive: Receive = {
>> case request: HttpRequest =>
>> val requestId = UUID.randomUUID()
>> request match {
>> case HttpRequest(GET, Uri.Path("/"), _, _, _) =>
>> notFound(requestId, request) // todo Implement this
>> case HttpRequest(POST, Uri.Path("/hello"), _, _, _) =>
>> invokeActor(classOf[HelloActor], requestId, request)
>> case HttpRequest(GET, Uri.Path("/users"), _, _, _) =>
>> invokeActor(classOf[ListUsersActor], requestId, request)
>> case HttpRequest(GET, Uri.Path("/addUser"), _, _, _) =>
>> invokeActor(classOf[AddUserActor], requestId, request)
>> case uri =>
>> notFound(requestId, request)
>> }
>> case msg => log.warning("Received unknown message: {}", msg)
>> }
>>
>>
>> private def invokeActor(actorType: Class[_], requestId: UUID, request:
>> HttpRequest) = {
>> context.actorOf(Props(actorType, sender(), requestId, request),
>> requestId.toString)
>> }}
>>
>> This allows me to fork off PRAs as needed but it kind of stinks in one
>> way because there are a lot of tools in the DSL for unpacking entities and
>> so on that I cant use, or rather if there is a way I and neither I nor
>> anyone within the reach of google has figured it out.
>>
>> So what am I missing? Do people really love this monstrous DSL even
>> though in a 100 endpoint system the thing will be gargantuan? Is there a
>> means to fork off at any point in the DSL and then "reboot the stream"? It
>> would be nice if some of the DSL tools could be invoked arbitrarily inside
>> the PRAs on the request object like.
>> class OrderPRA(replyTo: ActorRef, requestId: UUID, request: HttpRequest)
>> {
>>
>> // ... code
>> sender.tell(withRequest(request) {
>> entity(as[Order]) { order =>
>> complete {
>> // ... write order to DB
>> "Order received"
>> }
>> }
>> }), self)
>> }
>>
>>
>> Opinions? Thoughts?
>>
>>
>>
>>
>>
--
>>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>> Check the FAQ:
>>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user
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