Feature request for AuRa: using getPendingValidators() getter instead of InitiateChange event

[varasev]

We agreed that we'll use the getValidators() getPendingValidators() getter instead of catching the InitiateChange event. Parity should just read the current validator set with getValidators() getPendingValidators() every block, and if it discovers that the set is changed in the contract, it launches changing of the set in the engine.

The finalizeChange() function (described in https://wiki.parity.io/Validator-Set.html) should be called by Parity after newValidatorSet() is called and the internal list of validators is updated in engine (this is default behavior for AuRa in Parity, so I think the code of the engine shouldn't be changed for that).

UPDATE: stroke out things below are already implemented by the contracts.

Parity must call newValidatorSet() function by SYSTEM_ADDRESS once a week.

Since in AuRa the block time is determined (5 seconds), the ValidatorSet contract will keep track of elapsed time by itself, so there is no need to measure 1 week in Parity.

1 week = 120960 blocks

Parity must call the newValidatorSetCallable() getter every block and check whether to call newValidatorSet.

So, if newValidatorSetCallable() returns true, the newValidatorSet() must be called at the end of the current block.

Important note: transaction of calling newValidatorSet() must be included in a block before transaction of calling BlockReward.reward().

[varasev]

The description ⬆️ was updated:

1. I propose not to measure 1 week (duration of staking epoch) in Parity. We can do this in the contract.

2. It seems that Parity already uses getValidators() getter to verify that the internal list of validators is the same as the list in the contract. The internal list and contract's list should be identical. So, we need to use a getter with another name: getPendingValidators().

I'll update the contract's code accordingly.

[varasev]

Important note: transaction of calling newValidatorSet() must be included in a block before transaction of calling BlockReward.reward().

[DemiMarie]

@varasev can it be called by BlockReward.reward()?

[varasev]

@DemiMarie hmm, it's a good proposal. I'll check if this breaks something in the code. Thanks for the thought.

[DemiMarie]

@varasev The first thing that newValidatorSet() does is

require(newValidatorSetCallable());

So we can just change it to:

if (!newValidatorSetCallable()) {
    // do nothing
    return;
}

and just call it from BlockRewardAuRa.reward().

[varasev]

Yes, I've modified the contracts in accordance with this: https://github.com/poanetwork/pos-contracts/blob/8d10a85ad87633a54a7444883b32687faf5b80bf/contracts/BlockRewardAuRa.sol#L38-L39

So, now we don't have to modify the AuRa source code for calling newValidatorSet().

However, we still need to read getPendingValidators() instead of InitiateChange event.

I've updated the description above and changed the title.

[DemiMarie]

Fixed by #53

[afck]

Reopening; see #71 (comment).

[afck]

@DemiMarie, @varasev: I see this has been reverted on aura-pos. I guess it can be closed again, in favor of #71?

[varasev]

@afck Yes, I'm closing this.