Simple udp server with netty 4.1 and kotlin

UdpServer.kt

import io.netty.bootstrap.Bootstrap
import io.netty.channel.ChannelHandlerContext
import io.netty.channel.SimpleChannelInboundHandler
import io.netty.channel.nio.NioEventLoopGroup
import io.netty.channel.socket.nio.NioDatagramChannel
import io.netty.util.CharsetUtil
import io.netty.util.concurrent.DefaultThreadFactory
import kotlinx.coroutines.experimental.async
import kotlinx.coroutines.experimental.newFixedThreadPoolContext


fun main(args: Array<String>) {
    val port: Int
    if (args.isNotEmpty()) {
        port = Integer.parseInt(args[0])
    } else {
        port = 5514
    }
    DiscardServer(port).run()
}

class DiscardServer(private val port: Int) {
    private val acceptFactory = DefaultThreadFactory("accept")
    private val acceptGroup = NioEventLoopGroup(1, acceptFactory)

    @Throws(Exception::class)
    fun run() {
        val b = Bootstrap()
        b.group(acceptGroup)
                .channel(NioDatagramChannel::class.java)
                .handler(Handler())
        b.bind(port).sync()
    }

    fun shutdown() {
        acceptGroup.shutdownGracefully()
    }

}

class Handler : SimpleChannelInboundHandler<io.netty.channel.socket.DatagramPacket>() {

    private val coroutineContext = newFixedThreadPoolContext(4, "LogPool")

    override fun channelRead0(ctx: ChannelHandlerContext?, msg: io.netty.channel.socket.DatagramPacket?) {
        if (msg != null) {
            val message = msg.content().toString(CharsetUtil.UTF_8)
            async(coroutineContext) {
                System.err.println(Thread.currentThread().name)
                System.err.println(message + "\r\n")
            }
        }
    }

}