2024-06-29

TOTSCO correlationID

RESOLVED! See below!

My latest concern is understanding TOTSCO specification. This may be that I have mis-read or not read enough. I am fully prepared to accept I have this wrong. It came up because the buddy CP and myself read it differently.

Messages each way have a source and destination correlationID. This is necessary to allow a response to be correlated with a request. An initial request does not need a destination correlationID (indeed, should not have one), but needs a source, and the reply needs a destination correlationID matching that source (and arguably maybe not a source of its own, expect it is mandatory §2.1.5, except it is not §2.1.8).

My initial interpretation was that each message type that was a Request would have a response that is a Confirmation or a Failure. And that the Request/Confirmation or Request/Failure would need matching correlationID so the response could be matched to the request, but that was it.

Indeed, all of the messages and responses that progress a switching order also contain a switchOrderReference, so no actual need for correlationID at all anyway in those.

My code would send a Request and wait for a response, using the correlationID to match the response. This is synchronous in the customer order process where the SLA for a match request is 60 seconds. We make the customer wait for the response up to 61 seconds.

But then I saw the published TOTSCO test cases, and they all had a destination correlationID for the ongoing messages, the residentialSwitchOrderRequest, for example.

This only made sense if the whole sequence, such as the following, were all a single message flow with a consistent set of correlationIDs each way for the whole sequence.

  • residentialSwitchMatchRequest
  • residentialSwitchMatchConfirmation
  • residentialSwitchOrderRequest
  • residentialSwitchOrderConfirmation
  • residentialSwitchOrderUpdateRequest
  • residentialSwitchOrderUpdateConfirmation
  • residentialSwitchOrderTriggerRequest
  • residentialSwitchOrderTriggerConfirmation

If that is the case I have to hold correlationIDs much longer, and associate with ongoing switch orders. I spent many hours re-working the system to do just that. This had issues with the possibility of delayed/repeated messages, which can happen. A reply may be to an earlier message with the same correlationID. I'd far prefer the previous interpretation where each Request has a new and unique correlationID which has to be quoted in the single corresponding response (Confirmation or Failure). It would be simpler and easier. But the test case examples make it clear that this is not the case, which is messy and a lot more work.

I have now asked TOTSCO to clarify. I have not had a reply yet.

So, even though I did all the extra work, I am happy if they come back and say it is for each message pair distinctly. But they must update the specifications and examples and test case to make that clear, as it is a lot more work to track these over a complete (multiple days, weeks) switch order process than over a simple message pair.

For now my code does both - it tracks and uses consistent correlationID for the whole sequence of messages, but accepts new correlationIDs for each part of messages if that is what we get.

Update: "The specification does not call for either option to be a requirement, but our expectation and the behavior [sic] we have seen so far in testing is that the second option is being applied by users. There is nothing to stop a CP from wanting to use the same correlation ID throughout a whole switch journey, but the important thing is that they cannot expect their counterpart CP to follow the same behavior [sic]."

This is typically not helpful. If even one CP can expect / require the destination correlationID for a residentialSwitchOrderRequest to be their source correlation ID from previous residentialSwitchMatchConfirmation then that means all CPs will have to track correlationIDs through the sequence else they will not work with that CP. If a CP cannot expert / require that, then no CPs need to do that. The spec needs to say one way of the other. Saying "The specification does not call for either option to be a requirement" is a useless response!

Update: Finally a straight answer - I wasted a day making my code work the same as the test cases, FFS.

"We would like to inform you that, according to the specification, a switch order request is not seen as a response to a match confirmation. Additionally, the TOTSCo hub does not require users to include a destination correlation ID in any request message."

1 comment:

  1. I wonder if TOTSCo could get the person who knows how the system works to write the specification?

    ReplyDelete

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