Question

I’m trying to implement a mina service where the response to the final message should be based on the previous messages. Each message (header (1), data (n), end (1)) should receive a response, but the response to the “end” message should be based on the “header”, and any “data” messages received as well as the “end” message. Currently, I’m routing the messages to an aggregator which completes when it finds a “header” and “end” message for a particular correlation id. Unfortunately, the response is being sent before (or at the same time?) the message is sent to the aggregator, so I don’t have access to the aggregated message (which contains all the data I need to build the correct response) when building the response.

Is there a way to do this without manually storing and accessing the accumulated data (that is, without re-implementing camel’s aggregator)?

Edit:

Route is something like:

<camelContext>
    <route>
        <from uri="mina:..."/>
        <process ref="messageProcessor"/>
        <aggregate>
            <process ref="completeMessageProcessor"/>
        </aggregate>
    </route>
</camelContext>

I left out some tags and attributes (correlationExpression, completionPredicate, strategyRef, etc.) for clarity.

The messages were being aggregated properly, and they were being processed properly when “completed” (that is, when aggregated). But the response sent back through the mina endpoint to the client was the one generated by the messageProcessor, never the one generated by the completeMessageProcessor.

For example (and yes, it’s a rather contrived example, but bear with me), let’s say the protocol involves the client sending a header message which includes the total number of data messages it expects to send. Then it sends a number of data messages, which might be different in number to what it expected to send. Finally, it sends a footer, or end, message. The server should then respond back with the difference between the expected number of messages and the actual number of messages. With the route as written, that is impossible, since the number of messages is not known by the messageProcessor, which only processes individual messages. The completeMessageProcessor, having the aggregated message (consisting of header, all the data, and the end) does know this number, but the response generated at that point is not propagated back to the mina endpoint.

Changing the parsing of the messages to generate a message only when entire composed message is received is not an option, since the server must respond to the individual messages.

Answer 1

off the top, my guess is that the messageProcessor is setting up the OUT message, but the completeMessageProcessor is setting up the IN message. The mina consumer response is expecting/using the OUT message instead.

you can add some logging to verify this. if this is the case, then you might change your messageProcessor to use the IN body instead (or use exchanges headers) and add a transform after your completeMessageProcessor to set the OUT body based on the IN body

<transform>
  <simple>${in.body}</simple>
</transform>

see this for more information: http://camel.apache.org/using-getin-or-getout-methods-on-exchange.html

UPDATE: after some discussion, the real issue is that the aggregator currently only handles “InOnly” exchanges