public void Handle(ExternalServiceMsg msg)
{
/* As established in the WebServiceEndpoint.asmx.cs comments, it's possible to
* receive duplicate messages from the web service. Ways to handle duplicates
* vary depending on business requirements, but for this example we'll assume
* that if we receive a message with the same ServiceTransactionIdentifier
* property value within 5 minutes, we should just ignore it.
*/
if (Data.LastSeen == DateTime.MinValue)
{
// This is the first message received, so set Saga data.
Data.ServiceTransactionIdentifier = msg.ServiceTransactionIdentifier;
Data.Payload = msg.Payload;
Data.LastSeen = msg.Timestamp;
// Publish an event for consumption by other subscribing services.
Bus.Publish <IExternalMessageReceivedEvent>(e =>
{
e.ServiceTransactionIdentifier = msg.ServiceTransactionIdentifier;
e.Payload = msg.Payload;
e.Timestamp = msg.Timestamp;
}
);
}
// If we request a new timeout on every message received, it results in a
// sliding 5-minute window. Every time we request a timeout, it clears the
// previous timeout for this Saga, so we won't get multiple notifications.
RequestUtcTimeout(TimeSpan.FromMinutes(5), null);
}
public void Process(string transactionID, string payload)
{
// Translate the incoming web request into a message
ExternalServiceMsg msg = new ExternalServiceMsg();
msg.ServiceTransactionIdentifier = transactionID;
msg.Payload = payload;
msg.Timestamp = DateTime.UtcNow;
// Send the message on the Bus
Global.Bus.Send(msg);
/* Because the web application is not transactional, as soon as we call
* Bus.Send(), the message is sent on the Bus and cannot be recalled.
*
* Since this is the end of the WebMethod, the web service will return
* a 200 OK status code to the client. This will inform the calling
* client that we successfully received and have taken ownership of
* the message.
*
* HOWEVER, it is still possible for a server crash or network
* interference to prevent the 200 OK status code from being received
* by the client. This can cause the client to resend duplicate
* messages. This is why we need to ensure that our receiver
* (ReceivingSaga.cs) is capable of gracefully handling duplicate messages.
*/
}
