Add gRPC query for `Counterparty` for a given client identifier

[crodriguezvega]

Given a request with a client identifier, the gRPC query returns the stored Counterparty (if it exists).

[vishal-kanna]

@crodriguezvega I would like to work on it

[crodriguezvega]

Hi @vishal-kanna. Thank you for volunteering to take the issue! After I wrote the issue I was thinking that it might be nice to have this gRPC endpoint do something slightly different. I will explain.

When a light client is created for the first time, it will not have any counterparty information, but we store the signer of the party that submitted the (the "creator" of the light client). So I was thinking that it could be better to have a gRPC query with a request like:

message QueryClientRequest {
  // client unique identifier
  string client_id = 1;
}

And a response like this:

message QueryClientResponse {
  string creator = 1;
  Counterparty counterparty = 2;
}

Then if one queries for a light client after it has been created but before the counterparty has been registered, then the response would contain only the creator. Once the counterparty has been provided and the creator address has been deleted (since it is not needed anymore), the response will have an empty creator and the information for the counterparty.

The query endpoint would then be something like:

rpc Client(QueryClientRequest) returns (QueryClientResponse) {
  option (google.api.http).get = "/ibc/core/client/v1/clients/{client_id}";
}

Let me check with the team what they think and if they agree, then I will ping you back here to work on it. Thanks!

[crodriguezvega]

@vishal-kanna Got quick positive replies about the proposal in the comment above, so you can go ahead and work on it. Thank you!

[DimitrisJim]

handled in #7120