java.lang.IndexOutOfBoundsException Exception using Netty in a packet system

Question

I am currently programming a system that communicates via packets. This also works. I have one server and theoretically infinite clients. When I start only one client, it works very well, but when I start several, I always get a java.lang.IndexOutOfBoundsException exception after the program has worked for 2-3 minutes.

The Exception

WARNUNG: 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.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(77) + length(36) exceeds writerIndex(112): PooledUnsafeDirectByteBuf(ridx: 77, widx: 112, cap: 112)
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:478)
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:276)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
        at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:102)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
        at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:795)
        at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:480)
        at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:378)
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.lang.Thread.run(Thread.java:748)

Caused by: java.lang.IndexOutOfBoundsException: readerIndex(77) + length(36) exceeds writerIndex(112): PooledUnsafeDirectByteBuf(ridx: 77, widx: 112, cap: 112)
        at io.netty.buffer.AbstractByteBuf.checkReadableBytes0(AbstractByteBuf.java:1442)
        at io.netty.buffer.AbstractByteBuf.checkReadableBytes(AbstractByteBuf.java:1428)
        at io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:895)
        at io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:903)
        at eu.diamondcloudservice.wrapper.packets.incoming.PacketInCloudServerConnect.read(PacketInCloudServerConnect.java:79)
        at eu.diamondcloudservice.wrapper.network.PacketDecoder.decode(PacketDecoder.java:21)
        at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:508)
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:447)
        ... 19 more

Server main(String[] args)

EventLoopGroup eventLoopGroup = epoll ? (EventLoopGroup) new EpollEventLoopGroup() : (EventLoopGroup) new NioEventLoopGroup();
    try {
        ServerBootstrap serverBootstrap = new ServerBootstrap();
        serverBootstrap.group(eventLoopGroup);
        serverBootstrap.channel(epoll ? EpollServerSocketChannel.class : NioServerSocketChannel.class);
        serverBootstrap.childHandler(new ChannelInitializer<Channel>() {
            protected void initChannel(Channel channel) throws Exception {
                channel.pipeline().addLast(new NetworkHandler());
            }
        });
        channel = serverBootstrap.bind(networkConfiguration.getPort()).sync().channel();
        channel.closeFuture().syncUninterruptibly();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        eventLoopGroup.shutdownGracefully();
    }

Client main(String[] args):

EventLoopGroup eventLoopGroup = epoll ? (EventLoopGroup) new EpollEventLoopGroup() : (EventLoopGroup) new NioEventLoopGroup();
    try {

        io.netty.bootstrap.Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(eventLoopGroup);
        bootstrap.channel(epoll ? EpollSocketChannel.class : NioSocketChannel.class);
        bootstrap.handler(new ChannelInitializer<Channel>() {
            protected void initChannel(Channel channel) throws Exception {
                channel.pipeline().addLast(new NetworkHandler());
            }
        });

        channel = bootstrap.connect(networkConfiguration.getMasterHostname(), networkConfiguration.getMasterPort()).sync().channel();
        packetCaller = new PacketCaller(channel);
        packetCaller.sendPacket(new PacketOutVerify(networkConfiguration.getWrapperName(), networkConfiguration.getKey()));
        channel.closeFuture().syncUninterruptibly();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        eventLoopGroup.shutdownGracefully();
    }

channelActive in NetworkHandler:

public void channelActive(ChannelHandlerContext ctx) throws Exception {
    ctx.pipeline().addLast(new PacketEncoder());
    ctx.pipeline().addLast(new PacketDecoder());
    this.waitingForRegistration.add(ctx.channel());
}

PacketDecoder

@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf byteBuf, List<Object> output) throws     Exception {
int id = byteBuf.readInt();
Class<? extends Packet> clazz = Wrapper.IN_PACKETS.get(id);
if (clazz == null) {
  throw new NullPointerException("Could not find packet by id " + id);
}

Packet packet = clazz.newInstance();
packet.read(byteBuf, ctx.channel());
}

PacketEncoder

public class PacketEncoder extends MessageToByteEncoder<Packet> {
@Override
protected void encode(ChannelHandlerContext ctx, Packet packet, ByteBuf output) throws Exception   {
  int id = Wrapper.OUT_PACKETS.indexOf(packet.getClass());
  if(id == -1)
    throw new NullPointerException("Couldn't find packet of " + packet.getClass().getName());

  output.writeInt(id);
  packet.write(output, ctx.channel());
}
}

Answer 1

So there are multiple issues.

First of in PacketDecoder you need to first check if there are 4 bytes readable before trying to call byteBuf.readInt() . So something like:

protected void decode(ChannelHandlerContext ctx, ByteBuf byteBuf,      List<Object> output) throws Exception {
    if (byteBuf.readableBytes() < 4) {
        return;
    }
    int id = byteBuf.readInt();
    ...
}

Secondly in your Packet.read() method you also need to ensure that there are enough bytes readable and if not try again later