Add RPC for latest checkpoint

[bhgomes]

Signed-off-by: Brandon H. Gomes [email protected]

Description

Adds an RPC method for querying the latest checkpoint. This is useful for getting a loading bar for synchronization.

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Situational Notes:

• If adding functonality, write unit tests!
• If importing a new pallet, choose a proper module index for it, and allow it in BaseFilter. Ensure every extrinsic works from front-end. If there's corresponding tool, ensure both work for each other.
• If needed, update our Javascript/Typescript APIs. These APIs are officially used by exchanges or community developers.
• If modifying existing runtime storage items, make sure to implement storage migrations for the runtime and test them with try-runtime. This includes migrations inherited from upstream changes, and you can search the diffs for modifications of #[pallet::storage] items to check for any.
• If runtime changes, need to update the version numbers properly:
  • authoring_version: The version of the authorship interface. An authoring node will not attempt to author blocks unless this is equal to its native runtime.
  • spec_version: The version of the runtime specification. A full node will not attempt to use its native runtime in substitute for the on-chain Wasm runtime unless all of spec_name, spec_version, and authoring_version are the same between Wasm and native.
  • impl_version: The version of the implementation of the specification. Nodes are free to ignore this; it serves only as an indication that the code is different; as long as the other two versions are the same then while the actual code may be different, it is nonetheless required to do the same thing. Non-consensus-breaking optimizations are about the only changes that could be made which would result in only the impl_version changing.
  • transaction_version: The version of the extrinsics interface. This number must be updated in the following circumstances: extrinsic parameters (number, order, or types) have been changed; extrinsics or pallets have been removed; or the pallet order in the construct_runtime! macro or extrinsic order in a pallet has been changed. You can run the metadata_diff.yml workflow for help. If this number is updated, then the spec_version must also be updated
• Verify benchmarks & weights have been updated for any modified runtime logics

[stechu]

why a new RPC end-point? Should we just add the total number to the pull_ledger_diff (to reduce number of RPCs).

[stechu]

This PR requires merging #723 first.

[Garandor]

got the same thought as @ghzlatarev in https://github.com/Manta-Network/Manta/pull/712/files#r935325448 that it would be cheaper to bump the total number in storage on each TX and read a StorageValue instead of collecting the 256 shards on every single rpc call.

Intuitively, it sounds far more computationally expensive to have 257 storage reads per RPC instead of 2, especially in light of the recently merged #469

I think this'll need proper benchmarking - or some caching in the #686 where it only pulls a new value from the RT once per block and serves the rest from cache.

If we do the latter thing this LGTM. @bhgomes could you pls open a followup issue? Nvm, just realized that the #686 indexer IS the followup issue

[0xduracell]

got the same thought as @ghzlatarev in https://github.com/Manta-Network/Manta/pull/712/files#r935325448 that it would be cheaper to bump the total number in storage on each TX and read a StorageValue instead of collecting the 256 shards on every single rpc call.

Intuitively, it sounds far more computationally expensive to have 257 storage reads per RPC instead of 2, especially in light of the recently merged #469

I think this'll need proper benchmarking - or some caching in the #686 where it only pulls a new value from the RT once per block and serves the rest from cache.

If we do the latter thing this LGTM. @bhgomes could you pls open a followup issue? Nvm, just realized that the #686 indexer IS the followup issue

Yeah, we have discussed this. Will do it in the MantaPay 1.0.0.