Protocol filters

[oscar 12321 <os...@hotmail.com>]

I have a complex protocol to implement and I have started modifying the 
sumup example.

My protocol consists of messages all of then sent in and envelope  like 
this:

4 bytes: size of data
N bytes: the data
1 byte: tail mark.

Then each message inside the envelope (the data), contains a header byte 
with the type of message flllowed by the rest of fields of the message.

My question is: should i implement a stack of two protocol filters, one for 
the envelope (like the TextLineCodec), and other for the message data itself 
(perhaps a DemuxingProtocolCodec)?

Thanks in advance.

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Re: Protocol filters

[Trustin Lee <tr...@gmail.com>]

On 9/29/06, oscar 12321 <os...@hotmail.com> wrote:
>
> I have a complex protocol to implement and I have started modifying the
> sumup example.
>
> My protocol consists of messages all of then sent in and envelope  like
> this:
>
> 4 bytes: size of data
> N bytes: the data
> 1 byte: tail mark.
>
> Then each message inside the envelope (the data), contains a header byte
> with the type of message flllowed by the rest of fields of the message.
>
> My question is: should i implement a stack of two protocol filters, one
> for
> the envelope (like the TextLineCodec), and other for the message data
> itself
> (perhaps a DemuxingProtocolCodec)?


You just need one codec and one custom filter instead of two codecs:

1. Codec translates the message into an intermediary message.
2. Your filter translates the intermediary message (the data, envelope) into
the final message object.

Implementing a filter is very easy, so you will be able to implement the
translator shortly.

...
void messageReceived(NextFilter next, IoSession session, Object message) {
    IntermediaryMessage m = (IntermediaryMessage) message;
    ByteBuffer buf = m.getContent();
    ... do something with the buf ...
    next.messageReceived(session, newMessage);
}
...

HTH,
Trustin
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