Question

我目前正在评估Netty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 -

（类型）（子类型）（长度）（MessageBody）大小
＆lt; 4bytes＆gt;＆lt; 4bytes＆gt;＆lt; 4bytes＆gt;＆lt; ...＆gt; - 长度包括标题。

遵循Netty api I子类LengthFieldBasedFrameDecoder接收有效的完整数据包，然后根据收到的类型解码每个数据包。从我正在使用的文档 -

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

它工作正常大约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比消息大小短得多的ChannelBuffer。（我在崩溃前多次收到此消息）。然后我显然在我的内部解码代码中得到一个BufferUnderflowException。难道我做错了什么？使用LengthFieldBasedFrameDecoder时，是否应该保证消息的大小正确？

LengthFieldBasedFrameDecoder类 -

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;
    }


}

Answer 1

你需要调用super.decode（..）并在你的decode（..）方法中对返回的ChannelBuffer进行操作。

所以就像这样;

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;
    }
}

请务必查看大写评论。

从LengthFieldBasedFrameDecoder返回的缓冲区太小

1 个答案: