libdrizzle: failed non-blocking connects do not report error

[Evan Jones]

1. Use an external event loop with libdrizzle
2. Try to connect to a non-existent server.
3. The connect will succeed, but the next operation will fail.

The problem is that libdrizzle assumes the event loop will set POLLERR if the non-blocking connect fails. However, libdrizzle only ever passes POLLOUT to drizzle_con_set_events, and thus the external event loop never knows it should watch for errors. Worse, libevent, probably the most popular event loop library, never sets error indicators, and only ever sets the equivalent of POLLIN and POLLOUT. The reason, as far as I can tell, is that some polling mechanisms don't return error indications{

The attached patch fixes this by checking getsockopt to see if the connect succeeded or failed. I haven't tested this in libdrizzle itself (I maintain my own copy in my project), but this works for me. Thanks!

[Brian Aker (brianaker)]

See the attached branch (and confirm for yourself if it works).

[Evan Jones (evanj)]

Sorry; I'm not actively working on the project that uses libdrizzle any more, so it took me a while to verify this. It looks like it works to me: it now actually reports connection errors!