whats the best way to convert this code to a suspend method instead of returning a future? ``` fu...

# coroutines

[christophsturm]

whats the best way to convert this code to a suspend method instead of returning a future?

fun createCaptureServer(port: Int): CompletableFuture<String> {
        val future = CompletableFuture<String>()
        val undertow = Undertow.builder().addHttpListener(port, "127.0.0.1").setHandler {
            future.complete(it.queryString)
        }.build()
        undertow.start()
        return future.thenApplyAsync {
            undertow.stop()
            it
        }
    }

possibly using ktor instead of undertow.

[octylFractal]

if you're using ktor, it basically just becomes a normal function -- ktor's http methods are all suspend

[octylFractal]

wait, nvm

[octylFractal]

misread what was happening here

[octylFractal]

realistically I think it would be mostly the same, except you'd use a CompletableDeferred instead of Future

[Luis Munoz]

because it is a callbac I think this applies https://stackoverflow.com/questions/48552925/existing-3-function-callback-to-kotlin-coroutines/48562175#48562175

[octylFractal]

yes, you could do it that way as well

[octylFractal]

though I would recommend suspendCancellableCoroutine

[christophsturm]

thanks guys!

[christophsturm]

and how do do the thenApplyAsync part? (stop the http server)

[octylFractal]

use try-finally (assuming you go the suspendCancellableCoroutine route)

[christophsturm]

why is suspendCancellableCoroutine better? when would it cancel?

[octylFractal]

if you cancel the Job that the suspend function is a part of, then it properly cancels and throws an exception

[octylFractal]

otherwise it will just ignore cancellation

[octylFractal]

going to be honest, though, I don't see how to do this easily with suspendCancellableCoroutine -- I think that using the future model for actually retrieving the data is better

[octylFractal]

suspend fun createCaptureServer(port: Int): String {
  val deferred = CompleteableDeferred<String>()
  val server = <create server, with handler that completes the deferred>
  server.start()
  try {
    return deferred.await()
  } finally {
    server.close()
  }
}

is my take

[christophsturm]

suspend fun createCaptureServer(port: Int): String {
        val result =  suspendCoroutine<String>{cont->
            val undertow = Undertow.builder().addHttpListener(port, "127.0.0.1").setHandler {
                cont.resume(it.queryString)
            }.build()
            undertow.start()
        }
        undertow.close()
        return result
    }

this is what i came up with, but it does not work that way because undertow is inside the callback, so i would have to make it nullable and a var. which is not so great

[christophsturm]

so your solution is probably better

[christophsturm]

i ended up without finally, but thats probably just a matter of taste:

val deferred = CompletableDeferred<String>()
        val undertow = Undertow.builder().addHttpListener(port, "127.0.0.1").setHandler {
            deferred.complete(it.queryString)
        }.build()
        undertow.start()

        val result = deferred.await()
        undertow.stop()
        return result
    }

thanks for your help!

[octylFractal]

i'd be concerned about leaking the server in the case of an exception

[octylFractal]

but maybe you're okay with that