`AllowKnownQueryResponses` broken with new xcm router wrapper `WithUniqueTopic`

[JuaniRios]

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• [X] This is not a support question.

Description of bug

The new WithUniqueTopic wrapper on the XCM Router appends a SetTopic at the end of any xcm message sent.

The AllowKnownQueryResponses allows messages that only have 1 instruction, QueryResponse.

This means that if you submit a query through XCM, and the destination uses the WithUniqueTopic router, your barrier will reject all responses.

Proposed fix:

• Expect either 1 message containing the response, or 2 with the last one being the topic.

I can submit a fix soon

Steps to reproduce

• Send a message containing a query, like QueryPallet to a chain containing the WithUniqueTopic router.
• See in the logs how your barrier is rejecting the response.

[JuaniRios]

@franciscoaguirre

[bkontur]

@JuaniRios you need to wrap your barriers with TrailingSetTopicAsId, which is counter-part to WithUniqueTopic, you can try it e.g.:

TrailingSetTopicAsId<AllowKnownQueryResponses<..>>

There is also a test for TrailingSetTopicAsId.

We wrap all our barriers with TrailingSetTopicAsId, e.g. https://github.com/paritytech/polkadot-sdk/blob/master/cumulus/parachains/runtimes/assets/asset-hub-rococo/src/xcm_config.rs#L266

[JuaniRios]

@bkontur That's what I was looking for, thanks!