Can I leave and re-enter Sri Lanka on the same visa?

Yes. A normal tourist ETA can be used for two entries. That means you may leave and come back one time, as long as both visits fall within 30 days of your first arrival.

This rule works well for short regional trips. If you are away for longer than 30 days before returning, or if you want to enter for a third time, you will need to submit a new application and pay the fee for a new authorisation.