I'd like to start a discussion on handling WSRM in Synapse.

There are three aspects:

1. passthrough. In this model the sequence is from one endpoint to the other, and Synapse doesn't really get involved.
2. Synapse as an RM client. The message comes into Synapse, maybe over JMS or SMTP. We send it on with a sequence. Synapse is acting as an RM client (probably two-way).
3. Synapse is acting as an RM server and passing messages on without RM, perhaps to a "pre-RM" SOAP server, or via JMS.

1 isn't very interesting to us, tho we could do some special logging.
2 should be fairly straightforward. We need to be able to configure some aspects of the RM infrastructure - timeouts, the assignment of messages to sequences etc. I will propose a config model and syntax for this.
3 is a little tricky. The problem comes with "in-order" delivery. If this is enabled then synapse may need to hold up further processing of this  message until earlier messages have been delivered. Sandesha can take care of the "holding up", but we have no way currently of pausing a mediator or re-injecting a message partway through a mediator chain.

There are a few solutions to this I can think of:
A) Don't support inorder delivery - at least to start with. I think this might be a worthwhile first step, but it isn't a good long term solution as in-order is one of the main requirements people have for RM.
B) Add pausing or re-injection into Synapse. This would be some re-architecture. My main issue with this is that this is already built into Axis2 so I'm not keen on re-building it in Synapse as well if we can re-use the Axis2 capability instead.
C) This is a limited proposal but might be a reasonable model to start with. The idea is to split processing into two halves. The first half happens before RM "delivery" (i.e. before the inorder constraint is applied). The second half takes place after delivery. A simple syntax to handle this might look like:

<sequence>
   <reliableTerminate> <!-- i.e. we are terminating the RM connection in Synapse and passing on without RM -->
       <pre-delivery>
          mediators here
       </pre-delivery>
       <deliver/>
   </reliableTerminate>
   <mediator...> Any mediators here get called post delivery </med>
</sequence>

Paul


--
Paul Fremantle
VP/Technology, WSO2 and OASIS WS-RX TC Co-chair

http://bloglines.com/blog/paulfremantle
paul@wso2.com

"Oxygenating the Web Service Platform", www.wso2.com