When the Resend Request (2) message is received from the counterparty (e.g. due to a sequence number mismatch), OnixS::FIX::Session::ISessionListener::onResendRequest method is called if an application has previously subscribed to listening to session events. Otherwise, the SequenceReset-GapFill (4) message will be sent instead of the requested message.

If the sent application-level message should not to be resent to the counterparty then the overridden OnixS::FIX::ISessionListener::onResendRequest must return false. In this case the SequenceReset-GapFill (4) message will be sent instead (e.g. in case of an aged order).

The message that is about to be resent is available as an read only parameter in OnixS::FIX::ISessionListener::onResendRequest signature.