Comment by thesuperbigfrog

>> How does the caller know whether the response was empty because of an invalid session id ?

Documentation and how SQL database queries work.

The documentation states that a valid session id will return a SessionInfo struct (since it is an Option the type is Some(SessionInfo) ), and that an invalid session id will return None.

If the SQL query is something like "SELECT * FROM USER_SESSIONS WHERE USER_SESSION_ID = $1" then if an invalid session id is provided the database returns zero rows. The query was successful, but there were no matching sessions with that session id.

>> You have conflated empty response with an erroneous situation. The simplest solution is just Result<T, E>.

Again, an empty response is not an error in this situation. If your database query returns zero rows, is it an error? The database query succeeded. There are no sessions with the provided session id. What error occurred?