Error Handling

If an error occurs during the execution of the call request on the destination chain, and a rollback parameter was provided in the initial sendCallMessage method, the xCall contract on the source chain emits a RollbackMessage event. This event is triggered when an error occurs on the destination chain and a rollback operation is needed. The RollbackMessage event includes the serial number of the original request that needs to be rolled back.

The EOA on the source chain, after observing the RollbackMessage event, needs to invoke the executeRollback method on the xCall contract. This is done by passing the serial number of the original request that needs to be rolled back as an argument the same way as executeCall.

The destination chain does not pass back rollback instructions. These are defined up front in the _rollback parameter in the sendCallMessage method.

After the rollback operation is executed, the RollbackExecuted event is emitted by the xCall contract. This event notifies that the rollback has been executed and includes the serial number for the rollback, the execution result code, and a result message if any.