Using Acknowledgments

The BizTalk Messaging Engine generates positive acknowledgments (ACK) and negative acknowledgments (NACK) in response to conditions encountered during the processing of a message through a port. BizTalk Server publishes a positive acknowledgment to indicate successful transmission of a message and a negative acknowledgment to indicate transmission failure and suspension of a message.

Why Use Acknowledgments?

Positive and negative acknowledgments provide strong feedback that you can use to determine if a message arrived at its destination or encountered one or more problems along the way. For example, acknowledgments are useful when:

• You want to monitor a receive port for a new trading partner for schema validation and other errors.

• You want to mark the status of a loan request sent out for approval as "in process" if it is successfully sent to a partner for approval or "failed" if transmission fails (for example, if the partner's server is down).

• You process interchanges containing multiple purchase orders and want to track the number of orders that are transmitted or fail transmission.

  You can accomplish each of these scenarios by using acknowledgments and content-based routing that uses filters.

Routing Acknowledgments

When an ACK or NACK is published, all of the message context properties from the message that caused the ACK/NACK are demoted. Any properties that were promoted do not flow to the acknowledgment. To route an acknowledgment, build a filter using the following properties from the BTS namespace:

Negative Acknowledgment Message Body

Much of the important information about a positive or negative acknowledgment is contained in the context properties. In addition to the context properties, NACKs also contain a message body part containing a SOAP fault. The format of the SOAP fault is as follows:

<?xml version="1.0" encoding="utf-8"?>  
<SOAP:Envelope xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/" SOAP:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">  
  <SOAP:Body>  
    <SOAP:Fault>  
      <faultcode>Microsoft BizTalk Server Negative Acknowledgment </faultcode>  
      <faultstring>An error occurred while processing the message, refer to the details section for more information </faultstring>  
      <faultactor>C:\Projects\Sample\Locations\Response\FM_%MessageID%.xml</faultactor>  
      <detail>  
        <ns0:NACK Type="NACK" xmlns:ns0="http://schema.microsoft.com/BizTalk/2003/NACKMessage.xsd">  
          <NAckID>{FFB1A60B-E593-4620-8897-4E9C7030A937}</NAckID>  
          <ErrorCode>0xc0c01658</ErrorCode>  
          <ErrorCategory>0</ErrorCategory>  
          <ErrorDescription>There was a failure executing the send pipeline: "Microsoft.BizTalk.DefaultPipelines.XMLTransmit, Microsoft.BizTalk.DefaultPipelines, Version=3.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" Source: "XML assembler" Send Port: "Failed Message" URI: "C:\Projects\Sample\Locations\Response\FM_%MessageID%.xml" Reason: This Assembler cannot retrieve a document specification using this type: "http://Sample#Unknown".  </ErrorDescription>  
        </ns0:NACK>  
      </detail>  
    </SOAP:Fault>  
  </SOAP:Body>  
</SOAP:Envelope>  

The exception message raised by the adapter is in the SOAP Detail section in the ErrorDescription element.

Accessing the Message Body from an Orchestration

If you have an orchestration port that requires delivery notification, the DeliveryFailureException that is thrown on a transmission failure is deserialized from the SOAP fault that is contained in the NACK message body. To access the exception message string from within your orchestration, cast the DeliveryFailureException to a SoapException and then access the InnerXml as shown in the following code:

// Cast the DeliveryFailureException to a SoapException…  
System.Web.Services.Protocols.SoapException se = (System.Web.Services.Protocols.SoapException)e.InnerException;  
System.Diagnostics.Trace.WriteLine(se.Detail.InnerXml);  
//e is an Microsoft.XLANGs.BaseTypes.DeliveryFailureException  
//object type created in an Exception handler  

The preceding code sample returns an XML fragment similar to the following:

<?xml version="1.0" encoding="utf-8"?>  
<ns0:NACK Type="NACK" xmlns:ns0="http://schema.microsoft.com/BizTalk/2003/NACKMessage.xsd">  
  <NAckID>{FFB1A60B-E593-4620-8897-4E9C7030A937}</NAckID>  
  <ErrorCode>0xc0c01658</ErrorCode>  
  <ErrorCategory>0</ErrorCategory>  
  <ErrorDescription>There was a failure executing the send pipeline: "Microsoft.BizTalk.DefaultPipelines.XMLTransmit, Microsoft.BizTalk.DefaultPipelines, Version=3.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" Source: "XML assembler" Send Port: "Failed Message" URI: "C:\Projects\Sample\Locations\Response\FM_%MessageID%.xml" Reason: This Assembler cannot retrieve a document specification using this type: "http://Sample#Unknown".</ErrorDescription>  
</ns0:NACK>  

When Is an Acknowledgment Published?

Both positive (ACK) and negative (NACK) acknowledgments are published to the MessageBox database at the point of failure provided there is at least one matching subscription. For example, if BizTalk Server cannot find a matching schema for a message read from a receive port and there are no NACK subscriptions, it suspends the message (if failed message routing has not been enabled) and does not publish a NACK

See Also

Error Handling
Using Failed Message Routing