scala netty Discard Server sample

netty-discardserver.scala

package netty.sample

import io.netty.channel.ChannelHandlerContext
import io.netty.channel.ChannelInboundHandlerAdapter
import io.netty.buffer.ByteBuf
import io.netty.bootstrap.ServerBootstrap
import io.netty.channel.ChannelOption
import io.netty.channel.ChannelOption._
import io.netty.channel.ChannelFuture
import io.netty.channel.ChannelInitializer
import io.netty.channel.EventLoopGroup
import io.netty.channel.nio.NioEventLoopGroup
import io.netty.channel.socket.SocketChannel
import io.netty.channel.socket.nio.NioServerSocketChannel

class DiscardServerHandler extends ChannelInboundHandlerAdapter {

  override def channelRead(ctx: ChannelHandlerContext, msg: Object) {
    msg match {
      case b: ByteBuf => 
        println(b.toString(io.netty.util.CharsetUtil.US_ASCII))
    }
  }

  override def exceptionCaught(ctx: ChannelHandlerContext, cause: Throwable) {
    cause.printStackTrace
    ctx.close
  }
}

/**
 * Discards any incoming data.
 */
object DiscardServer {

  def main(args: Array[String]) {
  val bossGroup = new NioEventLoopGroup
	val workerGroup = new NioEventLoopGroup
    try {
      val boot = new ServerBootstrap()
      boot.group(bossGroup, workerGroup)
        .channel((classOf[NioServerSocketChannel]))
        .childHandler(new ChannelInitializer[SocketChannel]() {
          def initChannel(ch: SocketChannel) {
            ch.pipeline().addLast(new DiscardServerHandler())
          } 
        })
        .option[java.lang.Integer](ChannelOption.SO_BACKLOG, 128)        
        .childOption[java.lang.Boolean](ChannelOption.SO_KEEPALIVE, true)

      // Bind and start to accept incoming connections.
      val f: ChannelFuture  = boot.bind(8000).sync(); 
      // Wait until the server socket is closed.
      // In this example, this does not happen, but you can do that to gracefully
      // shut down your server.
      f.channel().closeFuture().sync();
    } finally {
	  workerGroup.shutdownGracefully()
	  bossGroup.shutdownGracefully()
    }
  }
}

netty-sample2.scala

package netty.sample

import io.netty.channel.ChannelHandlerContext
import io.netty.channel.ChannelInboundHandlerAdapter
import io.netty.buffer.ByteBuf
import io.netty.bootstrap.ServerBootstrap
import io.netty.channel._
import io.netty.channel.nio._
import io.netty.channel.socket._
import io.netty.channel.socket.nio._
import io.netty.handler.codec._

class DiscardServerHandler extends ChannelInboundHandlerAdapter {

  override def channelActive(ctx: ChannelHandlerContext) {
  val buf = ctx.alloc().buffer(100)
	buf.writeBytes("hello there".toCharArray.map(_.toByte))
	ctx.writeAndFlush(buf).addListener(new ChannelFutureListener() {
	  override def operationComplete(ch: ChannelFuture) {
	    //ctx.close
	  }
	})
  }

  override def channelRead(ctx: ChannelHandlerContext, msg: Object) {
    msg match {
      case b: ByteBuf =>
        val v = b.readByte
        println(v.toChar)
        if (v == 'q') {
          ctx.close
        }
        else {
          val res = ctx.alloc().buffer()
          res.writeByte(v)
          ctx.write(res)
          ctx.flush()
        }
    }
  }

  override def exceptionCaught(ctx: ChannelHandlerContext, cause: Throwable) {
    cause.printStackTrace
    ctx.close
  }
}

/**
 * Discards any incoming data.
 */
object DiscardServer {

  def main(args: Array[String]) {
	val bossGroup = new NioEventLoopGroup
	val workerGroup = new NioEventLoopGroup
    try {
      val boot = new ServerBootstrap()
      boot.group(bossGroup, workerGroup)
        .channel((classOf[NioServerSocketChannel]))
        .childHandler(new ChannelInitializer[SocketChannel]() {
          def initChannel(ch: SocketChannel) {
            ch.pipeline().addLast(new DiscardServerHandler())
          } 
        })
        .option[java.lang.Integer](ChannelOption.SO_BACKLOG, 128)        
        .childOption[java.lang.Boolean](ChannelOption.SO_KEEPALIVE, true)

      // Bind and start to accept incoming connections.
      val f: ChannelFuture  = boot.bind(8000).sync(); 
      // Wait until the server socket is closed.
      // In this example, this does not happen, but you can do that to gracefully
      // shut down your server.
      f.channel().closeFuture().sync();
    } finally {
	  workerGroup.shutdownGracefully()
	  bossGroup.shutdownGracefully()
    }
  }
}

class TimeEncoder extends MessageToByteEncoder[UnixTime] {
    def encode(ctx: ChannelHandlerContext, msg: UnixTime, out: ByteBuf) {
        out.writeInt(msg.t)
    }
}

Please, extend SimpleChannelInboundHandler[ByteBuf] instead of ChannelInboundHandlerAdapter.

It will require from you to override channelRead0 instead of channelRead method.
def channelRead0(ctx: ChannelHandlerContext, msg: ByteBuf): Unit

That will eliminate casting, because you will accept ByteBuf despite of java.lang.Object, and the most important: it will release ByteBuf automatically (And you don't). Please take a look at channelRead method:

https://github.com/netty/netty/blob/5725e804bcfbd0c76e0f11e7911a76970eb06c8c/transport/src/main/java/io/netty/channel/SimpleChannelInboundHandler.java

They are releasing resources. Unless you do it, your discard-server may leak.

Broken indentation on line 38 in netty-discardserver.scala, that's sad :(.