[mainde]

IMHO it's more: fix problems, or at least mitigate them, regardless whose problem it is.

I've been in this situation, a clientside bug meant that different requests arrived with the same idempotency key.

In my case, updating the client would have taken weeks, in the best case scenario. Updating the backend to check for a matching request body would have taken minutes, maybe hours.

It took me a surprising amount of arguing to convince people that, even if it was a clientside bug, we couldn't let users suffer for weeks in name of "correctness".

[amiga386]

Yeah but don't let them reify it.

Ideally you already send client version in requests (or have an API version prefix). Add the workaround only for legacy clients.

Next client version must distinguish itself from predecessor and must not require the bodge to work.

[mainde]

Well.. it was ~6 years and ~10 billion payments ago, the clients have been fixed but the "hack" is still there, it has caused no harm as far as I can tell. Worst case scenario it's useless, best case scenario it prevents regressions.

The issue with things that client must not do is that they might still do them, and users don't care whose fault it is. It's important to have auxilliary mechanisms to mitigate these.

[amiga386]

That it may be there or not doesn't mean it "caused no harm". It sounds like yet another carbuncle added in haste and then never fixed properly, leading to 6 years of fear of touching it.

If it's truly intended, it needs to be part of the official spec, with a robust justification of why it's there at all. Neither server nor client ought to have unnecessary and undocumented things "just in case", because that breeds a culture of uncertainty.

If you fear client regressions, make it a mandatory part of the client's test suite. You control the client, right?

[stingraycharles]

> In my case, updating the client would have taken weeks, in the best case scenario. Updating the backend to check for a matching request body would have taken minutes, maybe hours.

Then at least admit you’re just hacking quickly fixes, creating technical debt, and not fixing the actual problem.

I agree with your point that business interest is most important, I disagree that it’s the technically most appropriate solution.

The whole article is proclaiming that this is a technical problem about idempotency being hard, while it’s not. The whole premise of client side bugs must be resolved backend side as the correct solution is incorrect.

[mainde]

Eh, idk, I wouldn't classify these fixes as hacks nor as technical debt. It's labels that only work from a partial perspective. IMHO a solution that expects perfect compliance is not really complete, it's not good enough to put all the burden on the client, idempotency keys are part of the solution, but not the solution. So, in this sense I would say it is a technical problem.