How to get primary id from within a transaction

[jeffa5]

When executing a transaction (or on a command endpoint), it would be useful to be able to get the id of the leader (primary), similar to https://microsoft.github.io/CCF/main/operations/operator_rpc_api.html#get--node-consensus provides.

I can't see a way to get it from the internal map either and the logic the above endpoint uses isn't exposed.

[eddyashton]

The reason this isn't exposed is that the primary changes outside of the transaction order. So different nodes may return different primaries for otherwise identical requests. We're wary of letting apps make decisions within a transaction that depend on their (transient, local) opinion of the current primary.

What's the use case?

[jeffa5]

Building a custom status endpoint in the application that can return cluster-level information in a custom format. In this instance gRPC. It being only on readonly and command endpoints would be all I need. I agree that it could be troublesome if users included it in transactions that wrote to the maps. It isn't expected to be 100% accurate either, just a best guess so staleness is ok.