Reuse public createDispatcher

[AlixBa]

Allows custom wrapper to overload requestInternal MessageHandler.

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Hello,

So this is a naive proposal, but I'd like to know if we could find something around this. I've been working on OTel for NATS recently and I noticed a behavior on the java agent that I can not reproduce on the library.

If I instrument MessageHandler on the agent to create both receive and process spans on onMessage, I see that for a request, I have the following sequence/spans:

1. producer publish (subject:sub, replyTo: _INBOX.x)
2. consumer receive (subject: sub)
3. consumer process (subject: sub)
4. consumer publish (subject: _INBOX.x)
5. producer receive (subject: _INBOX.x)
6. producer process (subject: _INBOX.x)

Which is a very good thing to troubleshoot server latencies between 4-5.

On the other hand, not using the agent, I can not overload the dispatcher created since it's not exposed anywhere. This little change reflects what could be done to have a better observability (I don't like the cast, though).

Thanks

[scottf]

@AlixBa
In Connection Options you can set the DispatcherFactory

public Builder dispatcherFactory(DispatcherFactory dispatcherFactory)

There is a real use example here: https://github.com/nats-io/nats-java-vertx-client/tree/main/src/main/java/io/nats/client/impl

[AlixBa]

I'll have a look, thanks for the hint, I totally missed it