Netty自定义DelimiterBasedFrameDecoder

本文介绍了Netty自定义DelimiterBasedFrameDecoder的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我的公司正在探索使用Netty Framework实施消息路由器的可能性.将要路由的消息来自许多不同的来源，并且都有各自的格式.在大多数情况下，消息采用XML格式，其中包含包含正文长度的标头.但是，我们有一个供应商，其信息是不同的，并且不包含正文的长度.

My company is exploring the possibility of using the Netty Framework to implement a message router. The messages that it will be routing come from many different sources and all have their own formats. In most cases the messages are in XML which includes a header that contains the body length. However we have one vendor who's message are different and don't contain the length of the body.

此供应商消息包含HEADER，BODY和TRAILER.标头是1个字节，是STX(0x02)主体长度可变尾部为2个字节，其中包含一个ETX(0x03)和一个LRC.

This one vendors message contains a HEADER, BODY and TRAILER.The header is 1 byte and is an STX (0x02)The body is variable lengthThe trailer is 2 bytes which contain an ETX(0x03) followed by an LRC.

因此，典型的消息可能看起来像:

So a typical message might look like:

STX   BODY   ETX  LRC
02  37000000 06   18

我们最初使用DelimiterBasedFrameDecoder将ETX定义为定界符，但是当我们这样做时，我们会松开消息中的LRC字节.结果，LRC最终成为我们解码的下一条消息的第一个字节.有没有一种方法可以使用DelimiterBasedFrameDecoder并读取ETX分隔符之后的一个字节?

We initially used the DelimiterBasedFrameDecoder defining the ETX as the delimiter, however when we do that we loose the LRC byte that is part of the message. As a result the LRC ends up being the first byte of the next message that we decode. Is there a way to use the DelimiterBasedFrameDecoder and read one byte past the ETX delimiter?

此外，当我们将响应发送回源时，源将随后向我们发送一个ACK，我们也必须使用ACK来响应.

Further, when we send a response back to the source, the source will then send us an ACK which we have to respond to with an ACK as well.

我认为我们需要一个定制的解码器来读取该字节，如果它是ACK，则它会通知下一个处理程序，否则它将继续读取，直到它从ETX读取了1个字节，然后将该消息发送到下一个处理程序.看起来合理吗?在Netty中，是否有更好的方法或者我想使用的解码器代替DelimiterBasedFraneDecoder?

I am thinking that we need a custom decoder that reads the byte, if it is an ACK then it notifies the next handler, otherwise it continues reading until it reads 1 byte past the ETX and then sends that message on to the next handler. Does that seem reasonable? Is there a better way or is there a decoder in Netty that I might want to use instead of of the DelimiterBasedFraneDecoder?

对此我能提供的任何帮助，将不胜感激！

Any help that I can get on this is appreciated!

谢谢蒂姆

因此，在诺曼的建议下，我创建了以下解码器:

So at Norman's suggestion I created the following decoder:

public class MyDecoder extends DelimiterBasedFrameDecoder{

    public MyDecoder(int maxFrameLength, boolean stripDelimiter, ByteBuf delimiter) {
        super(maxFrameLength, stripDelimiter, delimiter);
        this.setSingleDecode(true);
    }

    @Override
    protected Object decode(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
        Object frame = super.decode(ctx, buffer);
        ByteBuf bufFrame = null;

    if(frame instanceof ByteBuf){
        bufFrame = (ByteBuf)frame;

        }else{
            System.out.println("OBJECT TYPE: " + frame.getClass().getSimpleName());
        }

        byte lrc = buffer.readByte();
        bufFrame.writeByte(lrc);
        return bufFrame;
   }

    public MyDecoder(int maxFrameLength, ByteBuf delimiter) {
        super(maxFrameLength, delimiter);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        super.channelActive(ctx);
        System.out.println("VERIFONE DECODER READY");
    }
}

我的处理程序使用以下命令初始化...

My Handlers are initialized with the following...

public class MyChannelInitializer extends ChannelInitializer<SocketChannel> {

    ByteBuf delimiter;
    byte[] ETX = {0x03};
    byte[] STX = {0x02};

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        setupDelimiter();
        ch.pipeline().addLast(new MyDecoder(65*1024, false, delimiter));
        ch.pipeline().addLast(new ByteArrayDecoder());
        ch.pipeline().addLast(new ByteArrayEncoder());
        ch.pipeline().addLast(new MyHandler());
   }

   private void setupDelimiter(){
       delimiter = Unpooled.copiedBuffer(ETX);

   }

}

一切正常，我得到了完整的消息，包括LRC，它是ETX之后的1个字节，但是它引发以下异常....

Everything works as expected, I get my full message including the LRC which is the 1 byte after the ETX, however it throws the following Exception....

May 09, 2014 5:11:43 PM io.netty.channel.DefaultChannelPipeline$TailHandler exceptionCaught
WARNING: An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It
usually means the last handler in the pipeline did not handle the exception.
io.netty.handler.codec.DecoderException: java.lang.NullPointerException
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:258)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:140)
at io.netty.channel.ChannelHandlerInvokerUtil.invokeChannelReadNow(ChannelHandlerInvokerUtil.java:74)
at io.netty.channel.DefaultChannelHandlerInvoker.invokeChannelRead(DefaultChannelHandlerInvoker.java:138)
at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:320)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:846)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:127)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:485)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:452)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:346)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:794)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at com.test.MyDecoder.decode(MyDecoder.java:33)
at     io.netty.handler.codec.DelimiterBasedFrameDecoder.decode(DelimiterBasedFrameDecoder.java:216)
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:227)
... 11 more

我不确定为什么会这样...

I am not sure why this is happening...

对我应该看的东西有什么想法吗?

Any thoughts on what I should be looking at?

谢谢蒂姆

the

Netty自定义DelimiterBasedFrameDecoder

问题描述

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