Given a URI like this:

mongodb+srv://user:pass@hostname/test

If there is a TXT record for hostname like "authSource=admin", then the driver should log into the admin database, not the URI's database "test". However, the authSource from the TXT record is ignored.

Cause: when we create a client or client pool, we call mongoc_topology_new, which copies the client's URI to the topology's URI, then updates the topology's URI with the contents of the SRV and TXT records. But then we create a "cluster" using the client's URI, which hasn't been updated.

This is going to be a bug factory so I'll open a ticket to clean it up and test it better. Meanwhile, just initialize the cluster with the topology's URI, not the client's.