ReplayingDecoder在解码时抛出异常

我创建了一个解码器来处理客户端发送的字节 . 就这个

import java.util.List;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ReplayingDecoder;

public class MessageDecoder extends ReplayingDecoder<DecoderState> {

    private int length;

    public MessageDecoder()
    {
        super(DecoderState.READ_LENGTH);
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf buf, List<Object> out) throws Exception{
        System.out.println(buf.readableBytes());
        switch(state()){
            case READ_LENGTH:
                length=buf.readInt();
                System.out.println("length is: "+length);
                checkpoint(DecoderState.READ_CONTENT);
            case READ_CONTENT:
                ByteBuf frame = buf.readBytes(length);
                checkpoint(DecoderState.READ_LENGTH);
                out.add(frame);
                break;
            default:
                throw new Error("Shouldn't reach here");
        }
    }
}

当客户端发送字节时，它会抛出下一个错误

io.netty.handler.codec.DecoderException：java.lang.IllegalArgumentException异常：minimumReadableBytes：-603652096（预期：> = 0）在io.netty.handler.codec.ReplayingDecoder.callDecode（ReplayingDecoder.java:431）在IO . netty.handler.codec.ByteToMessageDecoder.channelRead（ByteToMessageDecoder.java:245）at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:292）at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead（AbstractChannelHandlerContext.java:278） at io.netty.channel.DefaultChannelPipeline.fireChannelRead（DefaultChannelPipeline.java:962）at io.netty.channel.nio.AbstractNioByteChannel $ NioByteUnsafe.read（AbstractNioByteChannel.java:131）at io.netty.channel.nio.NioEventLoop.processSelectedKey （NioEventLoop.java:528）在io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized（NioEventLoop.java:485）在io.netty.channel.nio.NioEventLoop.processSelectedKeys（NioEventLoop.java:399）在io.netty . channel.nio.NioEventLoop.run（NioEve ntLoop.java:371）在io.netty.util.concurrent.SingleThreadEventExecutor $ 2.run（SingleThreadEventExecutor.java:112）在io.netty.util.concurrent.DefaultThreadFactory $ DefaultRunnableDecorator.run（DefaultThreadFactory.java:137）在爪哇 . lang.Thread.run（未知来源）

该代码来自官方文档http://netty.io/4.0/api/io/netty/handler/codec/ReplayingDecoder.html所以我真的不明白为什么它不起作用