从LengthFieldBasedFrameDecoder返回的缓冲区太小 [英] Buffer Returned from LengthFieldBasedFrameDecoder too small

问题描述

我目前正在评估Netty，以处理Java客户端与C ++服务器集成的套接字通信.消息传递协议具有以下结构-

I am currently evaluating Netty to handle socket comms for a Java client to integrate with a C++ server. The messaging protocol has the following structure -

• (类型)(子类型)(长度)(MessageBody)大小
• < 4bytes>< 4bytes>< 4bytes>< ...> -长度包括标题.

• (Type)(SubType)(Length)(MessageBody) with size
• <4bytes><4bytes><4bytes><...> - The Length includes the header.

在Netty api I子类LengthFieldBasedFrameDecoder之后，它接收有效的完整数据包，然后根据接收的类型对每个数据包进行解码.从我正在使用的文档中-

Following the Netty api I subclass LengthFieldBasedFrameDecoder to receive a valid full packet and then decode each packet depending on the type received. From docs I'm using -

• lengthFieldOffset = 8
• lengthFieldLength = 4
• lengthAdjustment = -12(= HDR1 + LEN的长度，负数)
• initialBytesToStrip = 0

它可以正常工作约5分钟(我每5秒左右收到一条消息)，然后解码事件包含一个ChannelBuffer，该ChannelBuffer短于消息的大小. (崩溃之前，我已经多次收到此消息).然后，我显然在我的内部解码代码中得到了BufferUnderflowException.难道我做错了什么?使用LengthFieldBasedFrameDecoder时，是否应该保证消息的缓冲区大小正确?

It works fine for about 5 minutes (I'm getting one message every 5 seconds or so) and then the decode event contains a ChannelBuffer that is much shorter than the size of the message. (I have received this message multiple times before the crash). I then obviously get an BufferUnderflowException in my internal decode code. Am I doing something wrong? Should I be guaranteed the correct sized buffer for the message when using LengthFieldBasedFrameDecoder?

LengthFieldBasedFrameDecoder类-

LengthFieldBasedFrameDecoder class -

public class CisPacketDecoder extends LengthFieldBasedFrameDecoder
{
    public CisPacketDecoder(int maxFrameLength, int lengthFieldOffset,
            int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip) {
        super(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment,
                initialBytesToStrip);       
    }

    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buf)
            throws Exception 
    {       
        CisMessage message = null;      
        int type = buf.getInt(0); //Type is always first int
        CisMessageType messageType = CisMessageType.fromIntToType(type);
        if(messageType != null)
        {
            message = messageType.getObject();
            if(message != null)
            {
                message.decode(buf.toByteBuffer());
            }
            else
            {
                System.out.println("Unable to create message for type " + type);
            }
        }

        //mark the Channel buf as read by moving reader index
        buf.readerIndex(buf.capacity());
        return message;
    }

}

并在此处实例化.

public class PmcPipelineFactory implements ChannelPipelineFactory 
{

    @Override
    public ChannelPipeline getPipeline() throws Exception
    {
        ChannelPipeline pipeline = Channels.pipeline();

        pipeline.addLast("encoder", new CisPacketEncoder());
        pipeline.addLast("decoder", new CisPacketDecoder(1024, 8, 4, -12, 0));      
        pipeline.addLast("handler", new MsgClientHandler());
        return pipeline;
    }


} 

推荐答案

您需要调用super.decode(..)并在您的encode(..)方法中对返回的ChannelBuffer进行操作.

You need to call super.decode(..) and operate on the returned ChannelBuffer in your decode(..) method.

所以会是这样；

public class CisPacketDecoder extends LengthFieldBasedFrameDecoder {
    public CisPacketDecoder(int maxFrameLength, int lengthFieldOffset,
            int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip) {
        super(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment,
            initialBytesToStrip);       
    }

    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buf)
        throws Exception {

        // THIS IS IMPORTANT!!!!!
        ChannelBuffer decoded = (ChannelBuffer) super.decode(ctx, channel, buf);
        if (decoded == null) {
            return null;
        }

        // NOW ONLY OPERATE ON decoded 
        CisMessage message = null;      
        int type = decoded.getInt(0); //Type is always first int
        CisMessageType messageType = CisMessageType.fromIntToType(type);
        if(messageType != null) {
            message = messageType.getObject();
            if(message != null) {
                message.decode(decoded.toByteBuffer());
            } else {
                System.out.println("Unable to create message for type " + type);
            }
        }
        return message;
    }
}

请务必检查大写注释.

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