Check-in algorithms

When a ticket is scanned at the entrance or exit of an event, we follow a series of steps to determine whether the check-in is allowed or not. To understand some of the terms in the following diagrams, you should also check out the documentation of the ticket redemption API endpoint.

Server-side

The following diagram shows the series of checks executed on the server when a ticket is redeemed through the API. Some simplifications have been made, for example the deduplication mechanism based on the nonce parameter to prevent re-uploads of the same scan is not shown.

Client-side

The process of verifying tickets offline is a little different. There are two different approaches, depending on whether we have information about all tickets in the local database. The following diagram shows the algorithm as currently implemented in recent versions of libpretixsync.