JSON RPC interface spec: chainHead_v1

[voliva]

More work for #801

This is the most important group of functions to be implemented from the spec. This makes PAPI already compatible except to send transactions (which needs the transaction_v1 group of functions).

It's not fully spec-compliant, specifically for the chainHead_v1_storage call, which has 2 variations that are more complex (closestDescendantMerkleValue, hash, descendantsHashes, and dealing with childTrie), but none of those features are used by PAPI. I rather make small incremental PRs, so I would initially focus on having full PAPI compatibility, and later on we can make it full spec compliant.

I'd also like to add tests, what do you prefer? Should I raise them as a separate PR or would you like it in this one? I'm thinking on keep raising incremental PRs, first I'll work on the tests for chainHead_v1, then implement transaction_v1 and its tests, and lastly chainSpec_v1 (the last group used by PAPI, but the least important).

[ermalkaleci]

Please add tests into this PR

[voliva]

@ermalkaleci I see that the e2e tests use PolkadotJS to test everything works as expected, but PolkadotJS doesn't use the new RPC-interface

Is it alright if I add polkadot-api (or a lower level sub-package) as a devDependency to run the e2e tests for the new rpc spec?

[ermalkaleci]

@ermalkaleci I see that the e2e tests use PolkadotJS to test everything works as expected, but PolkadotJS doesn't use the new RPC-interface

Is it alright if I add polkadot-api (or a lower level sub-package) as a devDependency to run the e2e tests for the new rpc spec?

of course, go ahead

[voliva]

I've finished adding tests - I had a bit of back-and-forth because I wasn't sure which level should I use for them.

One of the issues I had is that the block the tests run with is using a snapshot with a very old version of the metadata (v9 if I'm not wrong), which is not compatible with the higher-level papi libraries (since it relies on metadata v14+ to create the codecs)

Settled with @polkadot-api/substrate-client, since this just interfaces with the JSON RPC interface spec without encoding or decoding SCALE. I had to use polkadot.js to create some of the keys for the test.

[xlc]

you could add a new env for papi tests if it helps