Trustin Lee wrote:
>
> On 10/28/07, paul bryant <[EMAIL PROTECTED]> wrote:
>>
>> Hi
>> I have a very strange mixed up legacy protocol, where the message payload
>> can either be big or little endian depending on the payload type which is
>> contained in header (which is always big endian).
>> The header consists 4 16bit words as follows
>> 0xAA 0xAA Start Word
>> 0xXX 0xXX Total length in bytes
>> 0xXX 0xXX Payload Type
>> 0x00 0x0X Source ID
>> The paylaod size varies per Type but is 16bit word aligned.
>>
>> So I think I need to use a DemuxingProtocolCodecFactory with a set of
>> chained MessageDecoder's
>> Which will return MessageDecoderResult.NOT_OK if the payload type doesn't
>> match.
>
> Right.
>
>> Right there's the background here are the questions:
>>
>> 1. If the first decoder in the chain returns
>> MessageDecoderResult.NEED_DATA will the other decoders be called or will
>> the
>> IO handler keep calling the first decoder until the it returns OK or
>> NOT_OK?
>
> If you are referring to decodable() method, it will also call other
> decoders. For decode(), it will keep calling the first decoder until
> it returns OK or NOT OK.
>
>> 2. Can I swap endianness on the bytebuffer in each decoder in
>> isolation
>> or do I need to make sure the state of the bytebuffers endianness when I
>> return NEED_DATA or NOT_OK?
>
> You have to set the byte order of the buffer in every decode() method
> to make sure you are in the correct order. Please do not rely on the
> internal implementation detail of the DemuxingProtocolCodecFactory.
>
>> 3. Are there any examples of multiple chained decoders with binary
>> data
>> and mixed endians (Well I gotta ask).
>
> Unfortunately not yet. I think we need to provide an example for a
> multi-layered protocol, but not sure about mixed endians.
>
>> 4. Is the latest 1.1.3 ok for this or would 2.x be a better starting
>> point?
>
> It depends on how brave you are. :)
>
> 1.1.3 is enough IMHO though.
>
> Trustin
> --
> what we call human nature is actually human habit
> --
> http://gleamynode.net/
> --
> PGP Key ID: 0x0255ECA6
>
>
Trustin,
Have now implemented the protocol but have dealt with the endianess outside
of MINA
A good tutorial would be an excellent idea. Its a bit daunting to a newbie
how all the protocol/ message decoders fit together. In the end I just went
for it and experimented with it as I went until it worked. I suspect the
framework complexity (number of ways of doing the same thing) puts people
off using it.
One last question if may is there away of avoiding a "if else" tree in the
SessionHandler.
if (message instanceof Msg1)
{
}
else
if (message instanceof Msg2)
{
}
else
And so on
Thanks for the support
Paul
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