How to handle exception in decoders/handlers?

["이희승 (Trustin Lee)"]

Yes.  The telnet example would be a good start for you if you are trying
to write a String.  As you read from the user guide, Netty performs I/O
with ChannelBuffer.  You have to have something transforms a String into
a ChannelBuffer in the pipeline.

If you did not read the user guide yet, you got to.  Otherwise, please
let me know how the user guide could be improved so that a beginner
understands Netty better.

HTH,
Trustin

On 2009-06-20 오전 3:44, infectedrhythms wrote:
> 
> Is there a simple sample to follow?
> 
> Trustin Lee (via Nabble) wrote:
>> You need an encoder.
>>
>> On 2009-06-20 오전 3:21, infectedrhythms wrote:
>>
>>>
>>> Ok so now the exception is the last handler.
>>>
>>> But how do I write to the socket as
>>>
>>> @Override
>>> public void exceptionCaught(ChannelHandlerContext ctx, 
>> ExceptionEvent e) {
>>>
>>> e.getCause().printStackTrace();
>>>
>>> e.getChannel().write("Test");
>>>
>>>
>>> //ChannelFuture cf = ch.write("Test");
>>>
>>> //cf.addListener(ChannelFutureListener.CLOSE);
>>> //ch.close();
>>> }
>>>
>>> throws...
>>>
>>>
>>> java.lang.ClassCastException: java.lang.String cannot be cast to
>>> org.jboss.netty.buffer.ChannelBuffer
>>> at
>>>
>> org.jboss.netty.channel.socket.nio.NioWorker.writeUnfair(NioWorker.java:438) 
>>
>>> at 
>> org.jboss.netty.channel.socket.nio.NioWorker.write(NioWorker.java:411)
>>> at
>>>
>> org.jboss.netty.channel.socket.nio.NioServerSocketPipelineSink.handleAcceptedSocket(NioServerSocketPipelineSink.java:138) 
>>
>>> at
>>>
>> org.jboss.netty.channel.socket.nio.NioServerSocketPipelineSink.eventSunk(NioServerSocketPipelineSink.java:78) 
>>
>>> at org.jboss.netty.channel.Channels.write(Channels.java:626)
>>> at org.jboss.netty.channel.Channels.write(Channels.java:592)
>>> at 
>> org.jboss.netty.channel.AbstractChannel.write(AbstractChannel.java:203)
>>> at
>>>
>> com.rbs.threedsecure.mpi.services.broker.ThreeDHandler.exceptionCaught(ThreeDHandler.java:51) 
>>
>>> at
>>>
>> com.rbs.threedsecure.mpi.services.broker.ThreeDHandler.handleUpstream(ThreeDHandler.java:32) 
>>
>>> at
>>>
>> org.jboss.netty.handler.codec.frame.FrameDecoder.exceptionCaught(FrameDecoder.java:194) 
>>
>>> at 
>> org.jboss.netty.channel.Channels.fireExceptionCaught(Channels.java:440)
>>> at
>>>
>> org.jboss.netty.channel.AbstractChannelSink.exceptionCaught(AbstractChannelSink.java:59) 
>>
>>> at 
>> org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:293)
>>> at 
>> org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:280)
>>> at
>>>
>> org.jboss.netty.channel.socket.nio.NioWorker.readIntoHeapBuffer(NioWorker.java:300) 
>>
>>> at
>>>
>> org.jboss.netty.channel.socket.nio.NioWorker.processSelectedKeys(NioWorker.java:254) 
>>
>>> at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:163)
>>> at
>>>
>> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) 
>>
>>> at
>>>
>> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) 
>>
>>> at java.lang.Thread.run(Thread.java:619)
>>>
>>>
>>>
>>> Trustin Lee wrote:
>>>>
>>>> Hi,
>>>>
>>>> It seems like one of the handlers in your pipeline closes the 
>> connection
>>>> on an exceptionCaught event (perhaps the last handler.)  I would catch
>>>> the exception in the last handler and send the error message there
>>>> rather than sending it in the decoder, because it's often a good 
>> idea to
>>>> separate protocol state from codec.
>>>>
>>>> HTH,
>>>> Trustin
>>>>
>>>> On 2009-06-20 오전 2:42, infectedrhythms wrote:
>>>>>
>>>>> Hi, I have implemented a simple decoder and it works fine.
>>>>>
>>>>> Now if there is an error I want to throw an exception catch and reply
>>>>> back
>>>>> to the client, kind of like an HTTP 500 error.
>>>>>
>>>>> So if the decoder fails it should write back to the client the 
>> error that
>>>>> occurred.
>>>>>
>>>>> @Override
>>>>> protected Object decode(ChannelHandlerContext ctx, Channel channel,
>>>>> ChannelBuffer buf) throws Exception {
>>>>>
>>>>> ... do stuff here...
>>>>>
>>>>> throw new Exception("Errrorrrr!");
>>>>> }
>>>>>
>>>>> @Override
>>>>> public void exceptionCaught(ChannelHandlerContext ctx, 
>> ExceptionEvent e)
>>>>> throws Exception {
>>>>>
>>>>> super.exceptionCaught(ctx, e);
>>>>>
>>>>> e.getChannel().write("Damn it Jim!"); <-- Throws a
>>>>> ClosedChannelException
>>>>>
>>>>> }
>>>>
>>>>
>>>> --
>>>> — Trustin Lee, http://gleamynode.net/
>>>>
>>>>
>>>>  
>>>> _______________________________________________
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>>>>
>>>>
>>>
>>
>> -- 
>> — Trustin Lee, http://gleamynode.net/
>>
>>
>>
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>> Trustin Lee, Principal Software Engineer, JBoss, a division of Red Hat
>> -- 
>> what we call human nature is actually human habit
>> -- 
>> http://gleamynode.net/
>>
>>
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> 
> 
> 


-- 
— Trustin Lee, http://gleamynode.net/

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