FreeTDS Development Group

["James K. Lowden" <jklowden AT freetds.org>]

Frediano Ziglio wrote:
> > But there is an easy way: use connect(2) and write(2) instead of
> > sendto! connect(2) sets errno to ECONNREFUSED if no one is listening
> > to the port, even for UDP.
> 
>         /*
>          * on cluster environment is possible that reply packet came
>          from * different IP so do not filter by ip with connect
>          */
> 
> I think we can solve this problem using two sockets,
> one connected and another not connected.  

Possible conditions:

1.  gethostbyname() fails.  Don't try 1434. 
2.  connect/write/read to 1434 succeeds.  Hurrah!  
3.  connect/write/read to 1434 yields ECONNREFUSED.  Named instances
unsupported.  
4.  connect/write/read to 1434 times out.  Host down *or* host responding
from different interface.   

Well, first try connected.  It's quicker if it works, and it establishes
(#3) whether or not anyone's listening to 1434.  

For autodetection, for #4 I would assume the host is down, because
retrying is too slow (especially if it's actually a 5.0 server).  But if,
say, freetds.conf had "port = AUTO", then I'd try unconnected UDP.  I'm
also tempted to fork(2) and try both at the same time.  (The child could
write the results to the parent via a pipe.)  

--jkl