How do I upgrade .compile and .toService to finch 0.34?

[ComFreek]

Previously I had this code:

// ServerState is a custom class of mine
class ServerState { /* ... */ }

def getEndpoints(state: ServerState) =
  foo(state) :+: bar(state) :+: baz(state) /* and many more */

def getCompiledOverallEndpoint(state: ServerState): Endpoint.Compiled[IO] = {
  Bootstrap
    .serve[Application.Json](getEndpoints(state))
    .compile // ERROR: .compile doesn't exist
}

def getServiceForState(state: ServerState): Service[Request, Response] = {
  val filters = Function.chain(Seq(exceptionLogging, logging))
  Endpoint.toService(filters(getCompiledOverallEndpoint(state))) // ERROR: .toService doesn't exist
}

However, after updating to finch 0.34.1 the .compile and toService methods seem to no longer exist. How do I upgrade my code?

PS: Have you thought about supplying a detailed changelog in this repository?

[joroKr21]

I think those changes are from 0.34.0: https://github.com/finagle/finch/releases/tag/v0.34.0

[joroKr21]

You can call filter and toService directly on Bootstrap now:

Bootstrap[IO]
    .serve[Application.Json](getEndpoints(state))
    .filter(Function.chain(Seq(exceptionLogging, logging)))
    .toService

And it returns a Resource. Those changes were necessary to update to Cats Effect 3.

[ComFreek]

Thanks! With .filter I get a type error, but .middleware typechecks fine!

How do I use the Resource returned by .toService to create a runnable entry point (i.e., a Scala main method) that starts the server and listens forever?

I've tried the code below, but the server never starts and the application immediately exits:

class ServerState { /* ... */ }

object MyApp extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val state = new ServerState(/* some initialization */)

    createService(state).use(service => {
      Http.serve(":8085", service)

      IO.unit
    })
    
    IO.pure(ExitCode.Success)
  }

  private def createService(state: ServerState): effect.Resource[IO, Service[Request, Response]] = {
      Bootstrap[IO]
        .serve[Application.Json](getEndpoints(state))
        .toService
  }

  private def getEndpoints(state: ServerState) = foo :+: bar :+: /* ... */
}

[joroKr21]

You are throwing away the resource without using it. Bootstrap has a listen method you can use:

class ServerState { /* ... */ }

object MyApp extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val state = new ServerState(/* some initialization */)
    createService(state).use_.as(ExitCode.Success)
  }

  private def createService(state: ServerState) = {
      Bootstrap[IO]
        .serve[Application.Json](getEndpoints(state))
        .listen(":8085")
  }

  private def getEndpoints(state: ServerState) = foo :+: bar :+: /* ... */
}

[ComFreek]

Using your suggestion I am now getting the following output on stdout:

Aug. 09, 2023 4:24:55 PM com.twitter.jvm.Jvm$ liftedTree2$1
WARNING: failed to create Hotspot JVM interface, using NilJvm instead
Aug. 09, 2023 4:24:56 PM com.twitter.finagle.Init$ $anonfun$once$1
INFORMATION: Finagle version 22.12.0 (rev=ce0b60cecae0bc629dbe7720a1057ea2e99b424a) built at 20221226-043512
Aug. 09, 2023 4:24:56 PM com.twitter.finagle.filter.FiberForkFilter$ generateFiberFactory
INFO: Server has work-queueing fibers disabled

and then the application immediately exits (thus the server never listens indefinitely as intended). Any ideas what this might be?

I am using OpenJDK 19.0.2 on Windows 10 64-bit.

[joroKr21]

Oh sorry, I suggested the wrong function. resource.useForever instead of resource.use_ will keep it alive until it's interrupted.

[ComFreek]

Perfect! It works now.
For future visitors, this is the final version of the code that's working:

class ServerState { /* ... */ }

object MyApp extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
    val state = new ServerState(/* some initialization */)
    createService(state).useForever.as(ExitCode.Success)
  }

  private def createService(state: ServerState) = {
      Bootstrap[IO]
        .serve[Application.Json](getEndpoints(state))
        .middleware(Function.chain(Seq(/* ... */)) // e.g., logging, authentication
        .listen(":8085")
  }

  private def getEndpoints(state: ServerState) = foo :+: bar :+: /* ... */
}