finagle/finch

Try Cookbook (goo.gl/tFS8tx) before anything else!

Jan Bessai

@JanBessai

in my case, the resource is available while the endpoint module is alive

Jan Bessai

@JanBessai

ah I guess the correct way to do this is to expose the endpoint module itself as a resource, and later use it in the IO operation which starts the http server

Jan Bessai

@JanBessai

also, there is some issue with the documentation how to use AsyncStream, the api changed and it now has to be .toAsyncStraeam on the reader instead of AsyncStream.fromReader

Jan Bessai

@JanBessai

Seems AsyncReader finagle/finch#1070 and iteratee is the way to go. The documentation needs an according update!

Jan Bessai

@JanBessai

for those interested, here is what I ended up doing: https://github.com/combinators/expression-problem/blob/MajorCoreCleanup/jgitserv/src/main/scala/org/combinators/jgitserv/GitService.scala

thanks for the help! :)

iteratee gave me empty files and I found the documentation too sparse to work with, so I ended up using the future returned by Reader.fromStream(...).read()

Dermot Haughey

@hderms

anyone know if there is something stopping us from moving to circe 12.x

Octav Zaharia

@octavz

hi, this code:

      Bootstrap .serve[Application.Json](helloWorld :+: combos(env))

causes:

 no type parameters for method apply: (e: io.finch.Endpoint[FF,E])
io.finch.Bootstrap[FF,io.finch.Endpoint[FF,E] :: io.finch.Endpoint[zio.Task,String] :: shapeless.HNil,io.finch.Application.Json :: io.finch.Text.Plain :: shapeless.HNil] 
in class Serve exist so that it can be applied to arguments (io.finch.Endpoint[[+A]zio.ZIO[Any,Throwable,A],models.UserDTO :+:  models.CombosDTO :+: shapeless.CNil])
[error]       --- because ---
[error]      argument expression's type is not compatible with formal parameter type;
[error]       found   : io.finch.Endpoint[[+A]zio.ZIO[Any,Throwable,A],models.UserDTO :+: models.CombosDTO :+: shapeless.CNil]
[error]       required: io.finch.Endpoint[?FF,?E]
[error]
[error]      L77:             .serve[Application.Json](helloWorld :+: combos(env))
[error]                             ^
[error] [E2] Main.scala
[error]      type mismatch;
[error]       found   : io.finch.Endpoint[[+A]zio.ZIO[Any,Throwable,A],models.UserDTO :+: models.CombosDTO :+: shapeless.CNil]
[error]       required: io.finch.Endpoint[FF,E]
[error]      L77:             .serve[Application.Json](helloWorld :+: combos(env))

while:

Bootstrap
  .serve[Application.Json](combos(env))
  .serve[Application.Json](helloWorld)

will compile just fine, obviously some type inference doesn't work...

is :+: usable in my case ? am i doing something wrong ?

Both functions will return Endpoint[zio.Task, X]

Octav Zaharia

@octavz

same code compiles fine if i use cats.effect.IO instead of zio.Task

Sergey Kolbasov

@sergeykolbasov

it looks weird indeed
is type for helloWorld and combos set explicitly?

Thomas Santana

@nebulorum

I've been building in finch for a couple of week and using the Cookbook and user guide as much as possible. I really liked the idea of composing Endpoints. So I attempted to build one with mapOutputAsync and twitter.util.Futures.

def checkToken: com.twitter.util.Future[TokenInfo]  = ???
val authenticated: Endpoint[IO, TokenInfo] = header(Fields.Authorization).mapOutputAsync {
     checkToken(header).map(Ok)
}

This does not work since of header unlike get there are not Mapper for the future. I found a way via twitter Future to scala Future (form the cookbook with IO.pure, and IO.fromFuture). But I wonder if there is a way to do this without this step. I also tried to use io.catbirds.util but could not find a good way. Ony one have a better solution?

Sergey Kolbasov

@sergeykolbasov

@nebulorum You can look for inspiration here: https://github.com/finagle/finch/blob/master/core/src/main/scala/io/finch/internal/ToAsync.scala

Shortly, you need a conversion to IO anyway, but there is indeed a way to skip intermediate hop through Scala Future

Thomas Santana

@nebulorum

Shouldn't this conversion be applied on the other EndpointModules?

Thomas Santana

@nebulorum

This worked for me: def toIO[A](f: TFuture[A]): IO[A] = ToAsync.twFutureToAsync[IO].apply(f). However I feeling this is not the correct use. Is there a cleaner way?

Sergey Kolbasov

@sergeykolbasov

Yep, make checkToken returning you IO :)

I'd suggest to fallback to Future (if it's really required) somewhere on the very edge of the application where the actual I/O happens

Thomas Santana

@nebulorum

Sergey I get your suggestion of limiting the use of Future. From the looks of all Cat Effect/IO discussions Future is not the correct abstraction. But since Finch run on top of Finagle, doesn't it make sense to leverage the capabilities? Is there a more Effect way of using Finagle?

Sergey Kolbasov

@sergeykolbasov

@nebulorum there is no simple answer here, especially on "correctness" of abstraction.

Personally I'd prefer to use F[_] inside the application instead of fixing on a specific monad, would it be Future, IO or Task.

Speaking of Twitter Future, the only "killer feature" comparing to cats.effect.IO is LocalContext that is somewhat similar to Java's ThreadLocal and might be quite handy to use. I.e. monix Task provides similar capabilities.

We use ReaderT[IO, RequestEnv, *] monad instead to have the same set of capabilities but also keep referential transparency.

If you keep Future outside of your application logic, there is no difference from your app perspective on what happens outside

Octav Zaharia

@octavz

it looks weird indeed
is type for helloWorld and combos set explicitly?

@sergeykolbasov i was missing addSbtPlugin("org.lyranthe.sbt" % "partial-unification" % "1.1.2")

Thijs Broersen

@ThijsBroersen

When an exception is throw within one of the encoders the service returns a 500 and no error is logged. Is there any way I can add a specific exception handler to a service or part of a service, e.g. .serve[Application.Json](api).onErrorHandleWith(myhandler) ?

Ryan Plessner

@rpless

@ThijsBroersen you can use api.handle() in that case. Although I thought encoding errors also go through the Encoder for Exception which is usually what I've used for handling that

Dermot Haughey

@hderms

so we are using https://finagle.github.io/finch/cookbook.html#defining-custom-endpoints to do auth

we were figuring we'd be able to do something lke

withAuth :: someOtherEndpoint

withAuth being like Endpoint[User

but predictably there is no JSON encoder for User so this doesn't work

Dermot Haughey

@hderms

it seems like this form of composition just won't work for us which makes it hard for us to understand how we could blanketly add auth to a collection of endpoiints

from one perspective we could make sure User has a JSON codec and then perhaps it would work but it seems kind of hacky

Dermot Haughey

@hderms

I got it to work with an Endpoint[HNil] which isn't ideal but will more or less work for us

definitely was a bit confusing

Stefan Dietiker

@d-s-d

@hderms Why would you need an Encoder for User?

Dermot Haughey

@hderms

https://gist.github.com/hderms/9f8efdcf5895c6cf48bb52ea00cc416c something like this wouldn't compile

Alfredo Torre

@sentenza

Hey guys. I need some help here. I've just started using Finch and I was looking for a tutorial or some docs/examples on how to create a sort of "route decorator". I want to create a set of authenticated routes verifying JWT tokens produced by Auth0, but in order to do that I should execute a monadic flow (within cats.IO I guess) and check whether return a 401 or not at the end of the world.

Alfredo Torre

@sentenza

for instance in Play you can use the action composition to execute a check before executing the actual action like a sort of action decorator https://www.playframework.com/documentation/2.7.x/ScalaActionsComposition#Custom-action-builders

Ryan Plessner

@rpless

@sentenza are you using the old finch artifacts or the new finchx artifacts that make use cats effect? If you are using the ones with cats effect you can do something like this https://github.com/finagle/finch/blob/master/examples/src/main/scala/io/finch/middleware/Main.scala#L32

and only apply it to a subset of your endpoints

Frederick Cai

@zhenwenc

Hello, is there any good docs around for finchx? It's kinda confusing while reading the finch docs but using finchx :joy_cat:

Alfredo Torre

@sentenza

@sentenza are you using the old finch artifacts or the new finchx artifacts that make use cats effect? If you are using the ones with cats effect you can do something like this https://github.com/finagle/finch/blob/master/examples/src/main/scala/io/finch/middleware/Main.scala#L32

I'm using the new ones (finchx) so I guess that will solve my problem, but now I'm wondering how exactly I should take advantage of that middleware in my endpoints.

val auth: Endpoint.Compiled[IO] => Endpoint.Compiled[IO]  // where should I put the auth middleware?

val authFilter = Function.chain(Seq(auth))
val compiled = filters(Bootstrap.serve[Text.Plain](myEndpoint).compile)
// Endpoint.toService(compiled) ??

Is there any way to directly apply the authFilter on my endpoints?

Sergey Kolbasov

@sergeykolbasov

authFilter is just a function from Endpoint.Compiled to Endpoint.Compiled

so any compiled endpoint (in the example is myEndpoint) will be the subject of filtering once it's passed to the function

Sergey Kolbasov

@sergeykolbasov

However, Ryan mentioned that you can apply it only to subset of Endpoints. While in theory you can, you will end up with two compiled endpoints (that are just Kleisli) and combination of them is tricky, lawful one is even impossible, i.e. you can't distinguish 404 from endpoint not found and 404 from one of the endpoints as the resulting value. Therefore, you have to apply it to all the endpoints and check some preconditions in the middleware like path, method and whatever

If you don't like the case I mentioned and don't care about applicative nature of :: composition and the fact, that all the endpoints in this composition are evaluated to accumulate the errors, you can implement your own endpoint:

val auth: Endpoint[IO, HNil] = new Endpoint { .. } //or just header.mapOutputAsync depending on how you handle auth

And then compose it with those you need to protect:

get("foo" :: "bar" :: auth) { Ok("protected") }

Sergey Kolbasov

@sergeykolbasov

But beware that in :: composition all the endpoints evaluated unless one of them returns NotMatched. Since authentication for you is effectful, meaning it returns IO, you can't return NotMatched outside of IO. Therefore, you will have to return Matched result with failed output IO[Output] in case of authentication failure. In that case the rest of :: endpoints in the same composition scope are still evaluated for the sake of error accumulation. Say, you have JSON body to parse, then it'll be checked instead of failing fast. Nevertheless, Ok("protected") is never evaluated & returned if at least one of the endpoints in the corresponding composition fails with error, so in that context it's safe

Frederick Cai

@zhenwenc

Hi friends! I am wondering is there any tool available to document Finch endpoints, like swagger? Ideally auto(or semi-auto)-generated.

Sergey Kolbasov

@sergeykolbasov

No, sadly there is no tool to derive swagger from Finch endpoints

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