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From Ashish <paliwalash...@gmail.com>
Subject [MINA 3.0] Chain Transition aka nextFilter() Calculation mechanism
Date Thu, 10 Dec 2009 06:56:05 GMT
Folks,

Had a brief chat with Emm today regarding implementation of Filter
Transition mechanism.
Attached is the summary for further discussion(s)

Problem Statement
-------------------------
1. We need a way to determine next filter in chain
2. We need flexibility in the calculation mechanism for plugins like
users can plugin their own transition mechanism for eg State Machine
based

Summary
------------
The discussion was around the nextFilter API. There were two option,
have this in chain or have this in Filter. Having the API in chain was
a better option
as chain has access to the complete Filter list. So we are looking at
an API something like

IoFilter nextFilter(IoSession session);

or

IoFilter nextFilter(IoFilter currentFilter, IoSession session);

The second API is to cater to scenario where the chain needs to know
which the current/previous filter in the chain.

How it works
----------------
While the chain is being traversed, the IoFilters that have access to
the Chains, shall ask for the next Filter. Based on the return
type we call api like

messageReceived(..) {

//get next Filter

// fire next filter message received

}

Its two steps :-(.

The default Chain implementation shall be based on LinkedList.

So if someone wants to customize the way next filter is supposed to be
called, they can have custom implementation of nextFilter() API


Open for feedback on this. Please add if we have more

1. Does this API suffice to the needs that the Users may have? Alan,
will you be able to plugin State machine transition based on this

2. Do we need some specific TransitionFilter or some class in the
Filter chain that makes plugging in the implementation simpler.

Julien: will be able to handle the stateful codecs?

The stage is open for discussion :-)

-- 
thanks
ashish

Blog: http://www.ashishpaliwal.com/blog
My Photo Galleries: http://www.pbase.com/ashishpaliwal

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