BizTalk Send Ports, Delivery Notification and ACK / NACK messages
- by Robert Kokuti
Recently I worked on an orchestration which sent messages out to a Send Port on a 'fire and forget' basis. The idea was that once the orchestration passed the message to the Messagebox, it was left to BizTalk to manage the sending process. Should the send operation fail, the Send Port got suspended, and the orchestration completed asynchronously, regardless of the Send Port success or failure.
However, we still wanted to log the sending success, using the ACK / NACK messages. On normal ports, BizTalk generates ACK / NACK messages back to the Messagebox, if the logical port's Delivery Notification property is set to 'Transmitted'. Unfortunately, this setting also causes the orchestration to wait for the send port's result, and should the Send Port fail, the orchestration will also receive a 'DeliveryFailureException' exception. So we may end up with a suspended port and a suspended orchestration - not the outcome wanted here, there was no value in suspending the orchestration in our case. There are a couple of ways to fix this:
1. Catch the DeliveryFailureException (full type name Microsoft.XLANGs.BaseTypes.DeliveryFailureException) and do nothing in the orchestration's exception block. Although this works, it still slows down the orchestration as the orchestration still has to wait for the outcome of the send port operation.
2. Use a Direct Port instead, and set the ACK request on the message Context, prior passing to the port:
msgToSend(BTS.AckRequired) = true;
This has to be done in an expression shape, as a Direct logical port does not have Delivery Notification property - make sure to add a reference to Microsoft.BizTalk.GlobalPropertySchemas.
Setting this context value in the message will cause the messaging agent to create an appropriate ACK or NACK message after the port execution.
The ACK / NACK messages can be caught and logged by dedicated Send Ports, filtering on BTS.AckType value (which is either ACK or NACK). ACK/NACK messages are treated in a special way by BizTalk, and a useful feature is that the original message's context values are copied to the ACK/NACK message context - these can be used for logging the right information. Other useful context properties of the ACK/NACK messages:
- BTS.AckSendPortName can be used to identify the original send port.
- BTS.AckOwnerID, aka http://schemas.microsoft.com/BizTalk/2003/system-properties.AckOwnerID - holds the instance ID of the failed Send Port - can be used to resubmit / terminate the instance
Someone may ask, can we just turn off the Delivery Notification on a 'normal' port, and set the AckRequired property on the message as for a Direct port. Unfortunately, this does not work - BizTalk seems to remove this property automatically, if the message goes through a port where Delivery Notification is set to None.
