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From "Chris Audley" <chris.aud...@beacon-cs.com>
Subject IoFilter needs pre-connection callback (was: Proxy filter)
Date Thu, 07 Jun 2007 14:53:32 GMT
My question is, how can MINA be modified to make it possible for filters
to participate in the session before the connection is open and to
modify the parameters used to open the connection if necessary.

Yes, you've described how I can work around MINA's limitations in this
area to get a reasonably functional version of my proxy filter.
However, it is just that, a work around, and it substantially cripples
the proxy filter.

Consider the scenario where someone needs to be able to tunnel through
multiple proxies, for example one at the perimeter of the client network
and another at the perimeter of the server network.  If the proxy filter
didn't require a special IoConnector to work correctly, I could just
place multple instances of the filter in my filter chain and I'm off to
the races.  This isn't a theoretical question for me, I'm faced with
exactly this situation.

I have no problem figuring out a why to hack what I need together.  What
I would like is to find a way that MINA could be enhanced so that my
filters can be made generic enough to be added to the distribution.  It
is not uncommon for people to ask for such a filter on the mailing list.
Now that AsyncWeb is being added with most of the components necessary
to implement web proxy tunnelling, I'd like to see MINA include this
incredibly valuable -- and for many developers, necessary --
functionality.

How can MINA best support this functionality?  I think an additional
callback in IoFilter is needed.  In the case of the proxy filters, the
filter needs to be able to specify what the remote address should be
based on the service address.  Each proxy filter needs to see the
original service address to decide which proxy to use or even whether to
use the proxy (for example, maybe it doesn't proxy for local sub-nets).
It will also need to be able to determine what the remote address is
when "nextFilter" returns -- in case it was modified by another proxy
filter -- so it knows what address to connect to through the proxy.
Finally, it must be able to report what its has established as the
remote address for any proxy filters behind it in the chain.

Does anyone have a better idea?  Any thoughts on the best way to achieve
the requirements I've outlined?

-----Original Message-----
From: Niklas Therning [mailto:niklas@trillian.se] 
Sent: Thursday, June 07, 2007 2:54 AM
To: dev@mina.apache.org
Subject: Re: Proxy filter

Chris Audley wrote:
> I'd like to implement some proxy filters for MINA, filters that would 
> handle the details of opening a connection through a web or socks
proxy.
> The problem is, MINA filters have no influence over how the session is

> opened.  How can MINA be extended to give filters the opportunity to 
> redirect a session to a proxy address?
>
>   
Hi,

I guess you could implement an IoConnector to accompany your filter. The
IoConnector would need a SocketConnector to delegate to. When connect()
is called it will modify the remote address to point to the proxy
instead and then call connect() on the SocketConnector. It would also
add your proxy filter to the filter chain when a connection to the proxy
has been established. The proxy filter would then take care of the
authentication and initial handshake much like the SSLFilter does. Once
the proxy has established a connection to the original remote address
the proxy filter will have to notify the ConnectFuture returned by the
proxy IoConnector and call sessionCreated/sessionOpened.


--
Niklas Therning
www.spamdrain.net


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