Function check_state_independent_auth_rules 

pub(super) async fn check_state_independent_auth_rules<Fetch, Fut, Pdu>(
    rules: &RoomVersionRules,
    incoming_event: &Pdu,
    fetch_event: &Fetch,
) -> Result
where
    Fetch: Fn(OwnedEventId) -> Fut + Sync,
    Fut: Future<Output = Result<Pdu>> + Send,
    Pdu: Event,

Check whether the incoming event passes the state-independent authorization rules for the given room version rules.

The state-independent rules are the first few authorization rules that check an incoming m.room.create event (which cannot have auth_events), and the list of auth_events of other events.

This method only needs to be called once, when the event is received.

Errors

If the check fails, this returns an Err(_) with a description of the check that failed.