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List:       freediameter-dev
Subject:    [Dev]  Hold extension callback execution until PSM event occurs
From:       mbilski () eliberty ! pl (Michal Bilski)
Date:       2011-10-17 20:56:04
Message-ID: c8220f0fa7a4699bfe014541bd088e40 () eliberty ! pl
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Hello Sebastien,

I am currently working on a simple extension for freeDiameter that 
would allow to dynamically discover peers using DNS lookups. The 
extension registers an rt_out_cb that, in case when candidates list is 
empty, performs a series of DNS queries as described in RFC 3588/3588bis 
(NAPTR->SRV->A).

So far I am able to successfully connect to a peer discovered this way 
using fd_peer_add. The problem in this case is that it actually happens 
after the rt_out callback exits. Can you give me some hints on what 
would be the best way to hold it's execution until the peer state 
machine either enters STATE_OPEN or an error occurs for some reason 
(host unreachable, TLS handshake failed, etc.)? I have noticed that a 
callback for fd_peer_add can be provided, but I'm not exactly sure how 
to use it. It would require the extension to wait for some kind of event 
or change trigerred by the callback, and then decide if we can continue 
with this peer or we should fallback to try another one with less 
order/priority in DNS records tree. I think that this would be a better 
(and faster) way to notice peer state change, rather than periodically 
checking the state with d_peer_getstate.

I would appreciate any help form your side, including also any comments 
not directly related to the problem descirbed above, but to peer 
discovery in freeDiameter framework in general.

-- 
Best regards,
Michal Bilski


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