Race conditions between Auto-Update and administrative API calls

[m90]

The operator-facing Auditorium continuously polls the server for updates while open.

In rare cases, this can lead to race conditions like this:

• An Account is retired
• The request has been deleted already but the response is still pending
• Before the response is being sent and processed by the frontend (leading to log out) the Auditorium polls for an update
• This calls responds with a 403 now that the account does not exist anymore
• The user sees an error message, although retiring the account worked

Mar 19 13:52:45 offen-offen-dev offen[577]: - - - [19/Mar/2021:12:52:45 +0000] "DELETE /api/accounts/1bc8db1b-f32d-4376-a1cf-724bf6a597b8 HTTP/2.0" 200 -
Mar 19 13:52:45 offen-offen-dev offen[577]: - - - [19/Mar/2021:12:52:45 +0000] "GET /api/accounts/1bc8db1b-f32d-4376-a1cf-724bf6a597b8?since=xxxx HTTP/2.0" 403 -

There are two things to check here:

1. Retiring the account happens in a transaction here:

   offen/server/persistence/accounts.go

   Lines 263 to 289 in 7bba99e

   	func (p *persistenceLayer) RetireAccount(accountID string) error {
   	account, lookupErr := p.dal.FindAccount(FindAccountQueryByID(accountID))
   	if lookupErr != nil {
   	return fmt.Errorf("persistence: error looking up account to retire: %w", lookupErr)
   	}
   	if account.Retired {
   	return ErrUnknownAccount(fmt.Sprintf("persistence: account %s already retired", accountID))
   	}
   	txn, txnErr := p.dal.Transaction()
   	if txnErr != nil {
   	return fmt.Errorf("persistence: error creating transaction: %w", txnErr)
   	}
   	account.Retired = true
   	if err := txn.UpdateAccount(&account); err != nil {
   	txn.Rollback()
   	return fmt.Errorf("persistence: error retiring account %s: %w", accountID, err)
   	}
   	if err := txn.DeleteAccountUserRelationships(DeleteAccountUserRelationshipsQueryByAccountID(accountID)); err != nil {
   	txn.Rollback()
   	return fmt.Errorf("persistence: error deleting account user relationships for retired account %s: %w", accountID, err)
   	}
   	if err := txn.Commit(); err != nil {
   	txn.Rollback()
   	return fmt.Errorf("persistence: error committing account retiring: %w", err)
   	}
   	return nil
   	}

Does this properly commit the changes at the very end? Or does the polling call look at a transitional state here?

2. Is it possible to cancel pending fetch calls and block others while certain calls (like retiring) are being performed?