SMC Changes for a minimal sharding protocol

[prestonvanloon]

The research team has identified a few new changes in "spec 1.1" that they are confident will not be removed in a future specification.

High level requirements (please check off these as PRs are merged):

• Anyone can call addHeader(period_id, shard_id, chunks_root) at any time. The first header to get included for a given shard in a given period gets in, all others don’t. This function just emits a log.

• For every combination of shard and period, N collators (now called “notaries”) are sampled. They try to download the collation body corresponding to any header that was submitted. They can call a function submitVote(period_id, shard_id, chunks_root). This function just emits a log.

• Clients read logs. If a client sees that in some shard, for some period, a chunk has been included and >= 2N/3 notaries voted for it, it accepts it as part of the canonical chain.

Assigning to SMC expert @enriquefynn for now.
We should consider writing smaller tasks to achieve the above requirements unless this can be completed in 1 or 2 medium sized pull requests.

References:

• Sharding spec 1 <- Now out of date!
• Minimal sharding procotol <- The post that prompted this issue
• SMC modification - stage 1 ethereum/sharding#76 <- Excellent issue description by @hwwhww

[terencechain]

Adding new requirements after latest research thread:

• SMC initializes proposer_registry per shard which keeps track of proposer deposits
• proposer client calls get_eligible_proposer to sample per shard per period
• shard uses main chain block hashes delayed by 20 mins

Reference:
Expanding on proposer/notary seperation

[enriquefynn]

We shouldn't use "minutes" when talking about causal time dependencies, since we don't have a real time clock.

[rauljordan]

@terenc3t thoughts on integrating the changes from the proposer/notary separation into the minimal sharding protocol? We need something we can start implementing asap.

[terencechain]

@rauljordan We have enough information to start making changes on the SMC. I prefer we make incremental changes and open small/medium sized PR in parallel with the progress of the research side.

Besides p2p, what we can start implementing now:

• Proposer client can sample for getEligibleProposer() and call addHeader()
• Notary client can call submitVote()
• SMC emits logs for addHeader() and submitVotes()
• Client can listen to the logs

[terencechain]

Check out pyevm team's PR for notary registration. Excellent reference to follow along:

ethereum/sharding#77

[prestonvanloon]

Some hints in py-evm ethereum/py-evm#539

[rauljordan]

Being worked on in #93 already

[rauljordan]

@terenc3t and @prestonvanloon can we close this?

[terencechain]

Let's close this after #97. We are almost there