https://github.com/mongodb/mongo-ruby-driver/blob/master/lib/mongo/util/tcp_socket.rb#L63-83

There are a couple issues with this code:

1. Any time an ERRNO-based exception is raised, we should report that to the user, at least in the exception message.

2. The OperationFailure exception should be used only when MongoDB itself rejects the operation. For connection-level failures, we should raise ConnectionFailure.

3. What's the difference between ConnectionFailure and ConnectionError? Probably should stick to just one of these.