'Have we already responded to a transaction with the same id and
origin?
Returns:
Deferred: Results in `None` if we have not previously responded to
this transaction or a 2-tuple of `(int, dict)` representing the
response code and response body.'

@log_function
def have_responded(self, transaction):

    if (not transaction.transaction_id):
        raise RuntimeError('Cannot    persist    a    transaction    with    no    transaction_id')
    return self.store.get_received_txn_response(transaction.transaction_id, transaction.origin)
