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[mule-user] Service Chaining with Dynamic ReplyTo

by Todd Howitt :: Rate this Message:

I'm looking for an elegant way to handle a distributed operation and haven't found one yet. Here's the scenario:

Two separate containers, call them Remote and HQ. Remote exposes a WebService for local clients. This WebService sends each request through a JMS topic to HQ and waits for the reply on a temporary topic (nevermind why topics are being used; the requests are being routed from remote JMS brokers over very-small-aperture satellite to a cluster of HQ brokers using SonicMQ's DRA). HQ should handle each request by invoking a number of services serially/synchronously and sending the reply back via the message's embedded replyTo temporary topic.

The Remote WebService is implemented by a UMO that sends to a JMS endpoint through RequestContext.send(). It has an axis inboundEndpoint. The JmsMessageDispatcher creates the temporary topic replyTo for us. This works fine.

The HQ services are configured with the first service receiving on the JMS endpoint above. Its outboundEndpoint is set to a VM endpoint to another service, which is connected to a third service. This chain is a few services deep; your garden-variety Chain of Responsibility pattern.

My problem is that the first service at HQ sends its own results back rather than the results of its OutboundRouter (which represents the result of the services downstream). I see this happening in MuleProxy:

------onCall()------------

UMOMessage result = invoker.execute();
...

returnMessage = descriptor.getOutboundRouter().route(result,
event.getSession(),
event.isSynchronous());
...
replyToHandler.processReplyTo(event, result, replyTo);
--------------------------

In the case of a synchronous event, would it be possible to send returnMessage to the replyToHandler rather than result?

Such a feature would also allow the WebService on the Remote container to be a pass-through; configuring a synchronous outboundEndpoint would do the send operation and grab the result. Perhaps I could implement a generic UMO that uses java.lang.reflect.Proxy to masquerade as whatever WebService interface is configured for it. Essentially, it would allow an arbitrary chain of services (or a single service, for that matter) to look like a single WebService with no coding.

If that's not a desirable behavior, I'm looking for alternatives.

I've considered using a custom header to hold the reply endpoint, then configuring a special OutboundRouter on the last service to use it, but that would require some ugly hacks (getting the first service to not reply, configuring the last service to explicitly reply). The latter could conceivably be done using the replyTo property of OutboundRouters, but that's not dynamic; I need to reply to the temporary topic embedded in the message.

Any help?

Thanks,

-- Todd

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