On 17.02.2006, at 08:32, Niklas Therning wrote:
Simon Raess wrote:
hi
I'm trying to implement the BEEP protocol (RFC3080) on top of
Mina. Now, I have several questions relating to the implementation.
I've implemented a basic IoFilter that implements framing
according to the BEEP protocol. The next filter is supposed to
implement the transport specific mapping for TCP (RFC3081). This
mapping defines a sliding window mechanism for BEEP channels. The
TCP mapping filter needs to send a message back to the other side
to acknowledge messages (i.e. slide the window). An IoFilter has
access to the next filter. However, it does not have access to
the previous filter (to send the message). I know, I could use
the IoSession to send a message, but then it starts at the top of
the filter chain (correct?), i.e. it passes all the filters in
the chain, even the ones above the current filter (which is not
really what I'd like to do).
Actually, you do have access to the previous filter. Just call
nextFilter.filterWrite() in your filter if you need to write
messages. You see, NextFilter is the next filter for a particular
operation. In the case of filterWrite the next filter is actually
the filter *before* the current filter while for all other
operations (sessionOpened, messageReceived, etc) the next filter is
the filter *after* the current filter. This is always true no
matter which callback was called in your filter implementation.
I know it might be a bit confusing. :)
Sort of, but once you know it, it seems logical. :)
I'm wondering whether it is "a good idea" to send messages from
within the filters. Has anybody done that? Is it possible to pass
a message to the previous filter when receiving messages? Or
should I handle these issues in the protocol handler, possibly
using IoHandlerCommand or a layered protocol handler stack? Any
other suggestion, ideas?
Yes, it's very good idea. As I said SSLFilter works this way, as
does StreamWriteFilter. In fact, have a look at StreamWriteFilter.
It's a very good and easy to understand example of how it could be
done.
/Niklas
I'll have a look at the classes you suggested.
Thanks for the hints!
Simon
