Example of Asynchronous Socket Channel Pain

SocketPain.scala

import cats.effect._
import java.nio.channels.AsynchronousSocketChannel
import java.nio.ByteBuffer
import java.net.InetSocketAddress
import java.nio.channels.{AsynchronousSocketChannel, CompletionHandler}
import java.nio.{Buffer, ByteBuffer}

object Main extends IOApp {

  def run(args: List[String]): IO[ExitCode] = {
    IO{
      val client = AsynchronousSocketChannel.open()
      val hostAddress = new InetSocketAddress("localhost", 8080)

      val future = client.connect(hostAddress)
      future.get()
      
      println(client.getLocalAddress())
      println("Kill Server Now")

      System.console().readLine()
      // Thread.sleep(10000)

      val msg1 = "Hello, world".getBytes()
      val buf1 = ByteBuffer.wrap(msg1)
      val write1 = client.write(
        buf1,
        null,
        new IntCallbackHandler(cb => println(cb))
      )
    }.as(ExitCode.Success)
  }

  private final class IntCallbackHandler[A](cb: Either[Throwable, Int] => Unit)
      extends CompletionHandler[Integer, AnyRef] {
    def completed(result: Integer, attachment: AnyRef): Unit =
      cb(Right(result))
    def failed(err: Throwable, attachment: AnyRef): Unit =
      cb(Left(err))
  }

}