FreeTDS Development Group

[Peter Deacon <peterd AT iea-software.com>]

On Wed, 17 Dec 2008, James K. Lowden wrote:

> 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.)

Recommend using bind() rather than connect() with UDP.  With bind you 
still get ICMP indiciations for fast failure when send()ing.

Have Fun!
Peter