Netty hello world example not working

Question

I have following code to echo input received by Netty-

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class MyHandler extends SimpleChannelInboundHandler{


    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {

        ByteBuf in = (ByteBuf) msg;

        try {
            System.out.println(in.toString(io.netty.util.CharsetUtil.US_ASCII));
        } finally {
            in.release();
        }


    }
}

I am invoking it as follows-

 try {
            ServerBootstrap b = new ServerBootstrap(); // (2)
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class) // (3)
                    .childHandler(new ChannelInitializer<SocketChannel>() { // (4)
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new MyHandler());
                        }
                    })
                    .option(ChannelOption.SO_BACKLOG, 128)          // (5)
                    .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)

            // Bind and start to accept incoming connections.
            ChannelFuture f = b.bind(port).sync(); // (7)

            // 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();
        }

When I send a curl request to this Netty server, while I do see system.out working (I can see the curl request in console) I get this exception-

May 01, 2014 6:25:01 PM io.netty.channel.DefaultChannelPipeline$TailHandler exceptionCaught
WARNING: An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
    at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:102)
    at io.netty.buffer.WrappedByteBuf.release(WrappedByteBuf.java:819)
    at io.netty.buffer.SimpleLeakAwareByteBuf.release(SimpleLeakAwareByteBuf.java:34)
    at io.netty.util.ReferenceCountUtil.release(ReferenceCountUtil.java:68)
    at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:110)
    at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:341)
    at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:327)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:116)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:494)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:461)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:378)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:350)
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
    at java.lang.Thread.run(Thread.java:744)

What am I doing wrong? Using 4.0.18.Final with JDK 8.0 on Windows 7

Answer 1

You must not call ByteBuf.release() in the channelRead0(...) method as SimpleChannelInboundHandler will take care of this for you.