Call runtime API on top of any specified state

[liuchengxu]

Currently, the runtime API is limited to be called on top of a certain block, while in Subspace we have to call some APIs against an intermediate state between the entire block execution, for example, call BlockBuilder_finalize_block after all the extrinsics have been applied and before executing the finalize_block hook. It's less robust having to work with the String API like BlockBuilder_finalize_block even it's kind of stable, I'm wondering whether there is a way to call the runtime API against any specific state, seemingly doable to do something around contextual_call

substrate/client/service/src/client/call_executor.rs

Line 186 in 6506784

fn contextual_call<

Not sure if you think it's a generally useful feature and could be included into Substrate, and any suggestions on implementing this feature outside Substrate would be appreciated!

[bkchr]

That is something that would be needed by Cumulus as well: https://github.com/paritytech/cumulus/issues/874

So, I think it can be integrated into Substrate :)

[liuchengxu]

Do you already have some plan in your mind that what it could be done properly in Substrate? Just in case I work on the wrong track :D.

[bkchr]

No I don't have yet a proper plan. Probably something around implementing CallApiAt for some new type.