How ibc-go generate the existence proof of a packet?

[ImJeremyHe]

Summary of Bug

I have investigated for a while that how an existence proof is generated in ibc-go.
But I found that it is always nil in the response.

ibc-go/modules/core/04-channel/keeper/grpc_query.go

Line 223 in ceddad5

return types.NewQueryPacketCommitmentResponse(commitmentBz, nil, selfHeight), nil

I'm not sure whether this is the relevant code I am looking for.

Expected Behaviour

Version

Steps to Reproduce

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[crodriguezvega]

Hi @ImJeremyHe. The reason why the proof is nil in that response (and in the response of other gRPC queries of ibc-go) is the lack of support at SDK/Tendermint level for gRPC calls to return proofs for the query. There is this issue open in the SDK repo to add support for it.

The way to get the proof would be to make an ABCI query using either Tendermint's RPC endpoint or the SDK's gRPC endpoint that has been added recently (and released in v0.46).

I hope this helps!

[ImJeremyHe]

@crodriguezvega Thank you for your reply! Do you know where I can read the exact implementation of getting proof? There are so many relevant repo and I have no clue.

[crodriguezvega]

@ImJeremyHe Sorry for the late reply, but I didn't have the knowledge to be able to answer your question, until @AdityaSripal actually explained this week how it works.

When a relayer makes an ABCI query on Tendermint't RPC endpoint, Tendermint routes via ABCI the query to the SDK. From here, the steps to follow where a proof for data stored in IAVL is obtained are these: 1, 2, 3, 4, 5, 6, 7, 8 and finally inside this function the IAVL treeGetMembershipProof or GetNonMembershipProof functions are used to retrieved a proof depending on whether a existence or non-existence proof is needed.

I hope this helps!