Expected response exchange pattern SetOneWay

[Hooghof]

I was wondering which response I should expect if I send a message to an inbound https step with a SetOneWay step behind it. My expectation is that I will receive the original message as response. Is that right?

Test case
Instance: next
Tenant: Regression tests
Flow: CB_ExchangePatternOneWay

[skin27]

This is a very good question, but not super easy to answer. The short answer is:

The exchangePattern does not effect the exchange or the flow, but only effects the endpoints after it's it set.

This is the explaination given by ChatGPT:

setExchangePattern is a metadata flag, not a flow controller.
The pattern is simply a hint to Camel and its components:

InOut: the caller expects a reply.
InOnly: the caller does not expect a reply.

The setExchangePattern() is mainly intended to influence subsequent producers (such as JMS, HTTP).

The setBody(Y) call is what erases X — full stop, regardless of exchange pattern. If you deleted both setExchangePattern lines entirely and just did setBody(X) then setBody(Y), you'd still get Y back. The interleaved pattern changes are a red herring here: nothing in Camel ties a body value to "whatever the pattern was when I set it." There's one body slot, and it gets overwritten.

This is confirmed by Camel's own explanation of exchange internals: the MEP is just a flag on the Exchange which the Consumer and Producer adhere to, and you can change it at any time with setPattern. It's not tied to message content at all.

Maybe we should explain this clearer in the documentation, or just rename the step to "setEndpointInteractionToOneWay" of "setResponseModeAsReply" or something like that. Or just remove it, and only allow to set it on flow links.

[skin27]

Some additionals marks to make:

1. This is thus the expected (although confusion) respons of your test case.
2. On next I created for test cases with flowlinks and queus. Where I set the body in the first flow to 1, and in the second flow to 2. Every flowlink I set to "ExchangePattern=InOnly"

• FlowLink (synchronous) --> 2
• FlowLink Async --> 1
• Queue (synchronous) --> 1
• Queue (Async) --> 1

In the last 3 cases the InOnly is respected, because these use Asynchronous Camel components (Seda, and JMS), while in the first Direct is used. In this case the ExchangePattern is set, but only as a hint. You would get an InOnly back if in the second route contains an asynchronous endpoint like for example a http.

[skin27]

The official documetation of Apache Camel also have been updated:

https://camel.apache.org/manual/exchange-pattern.html