Socket: non-blocking connect and getsockopt SO_ERROR

Corinna Vinschen
Mon May 16 13:29:00 GMT 2011

On May 16 14:43, Jacob Eiler wrote:
> Hi.
> I am experiencing an issue with getsockopt when running an application
> under CygWin. 
> The application (Kannel sms gateway) creates a new socket, attempt to
> connect non-blocking to the other host and later calls getsockopt to
> check for errors:
> s = socket(PF_INET, SOCK_STREAM, 0);
> ...
> flags = fcntl(s, F_GETFL, 0);
> fcntl(s, F_SETFL, flags | O_NONBLOCK);
> ...
> connect(s, &addr, sizeof(addr))
> connect returns EINPROGRESS and the application has a polling thread
> setup to handle timeout and check for changes. In both cases a callback
> function is invoked.
> The callback function checks the connection by calling 
> getsockopt(s, SOL_SOCKET, SO_ERROR, &err, &len)
> but it returns 0 and no error - even if the connection was never
> established. Subsequently the application tries to write data to the
> socket - which fails with a "transport endpoint is not connected" error.
> The code works just fine on Linux with getsockopt returning an error.
> Any pointer on how to get this working will be greatly appreciated.

Use select.  I'm not sure the underlying Winsock implementation sets
the SO_ERROR value in the same way as on Linux.


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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