implement variant of subscription that returns finalized storage changes

[gregdhill]

Signed-off-by: Gregory Hill gregorydhill@outlook.com

Closes #238

• Adds RPC method to subscribe to finalized block headers and retrieve storage changes per block.
• Update extrinsic watcher to wait for finalization.
• Also fixes the method name for the following unsubscribe calls...

https://github.com/paritytech/substrate-subxt/blob/9959f0d29950219f20b5cc79dfff46f8987239fc/src/rpc.rs#L465
https://github.com/paritytech/substrate-subxt/blob/9959f0d29950219f20b5cc79dfff46f8987239fc/src/rpc.rs#L481

[gregdhill]

Hmm this feature might need to wait until after the jsonrpsee V2 upgrade since for some reason the finalized block subscription isn't dropped...

[ascjones]

I've merged #214 so you can update this branch now

[gregdhill]

@ascjones please review

[ascjones]

Overall looks good. As mentioned I do think we should still allow subscribing to non finalized events when submitting an extrinsic still if we want to trade immediacy for finality.

Was just looking at the polkadot.js api an they do it slightly differently with a status field: https://polkadot.js.org/docs/api/start/api.tx.subs/, but it's a bit more low level than what we have here.

[gregdhill]

@ascjones added a workaround to support configuration of the event subscription on submit_and_watch_extrinsic, let me know what you think!

[ascjones]

Yes that API looks fine, I'd like the comments expanding so it's clear exactly what is going on to avoid footguns.

[ascjones]

Perhaps instead of the two different methods we could just check the weak_inclusion flag like we do in the submit transaction method. Though you would need different client instances if you wanted to do both in that case. What do you think?

[gregdhill]

For now it's probably cleaner with two distinct methods as we also have subscribe_blocks and subscribe_finalized_blocks.

[gregdhill]

Anyway I think we should remove accept_weak_inclusion in favour of some config on the generated traits (like how it is done in polkadot{.js}) pending refactoring of the proc-macro crate.

[ascjones]

Branch needs updating with master.
Edit I see already done

[ascjones]

BTW the force pushes make it hard to review updates because I can't see just the changes since I last reviewed. Merge commits are fine.

[ascjones]

Great work!