Staking manager

For the Polygon’s Proof of Security based consensus, all the ⅔+1 proof verification and handling of staking, rewards are executed on the Ethereum smart contract. The whole design follows this philosophy of doing less on the Mainnet contract. It does information verification and pushes all the computation-heavy operations to L2 (read about Heimdall).

Stakers are divided into validators, delegators, and watchers (for fraud reporting).

StakeManager is the main contract for handling validator related activities like checkPoint signature verification, reward distribution, and stake management. Since the contract is using NFT ID as a source of ownership, change of ownership and signer won’t affect anything in the system.

Tip

From one Ethereum address, a Staker can only be a validator or delegator (it’s just a design choice, no hard reasons).

Validator admissions / replacement

Admissions

At present, there are no open validator slots available on Polygon PoS. There is also a waitlist to become a validator. In the future, if slots become available, validators may apply to be considered and removed off of the waitlist.

Replacement

PIP4 introduced the concept of showcasing validator performance for community visibility. If a validator is in an unhealthy state for an extended period of time as outlined in PIP4, they are off-boarded from the network. The validator slot is then made available to those coming off of the waitlist.

Info

Currently, Phase 2 of PART C in PIP4 is being implemented. This is where the community decides on validator prospect evaluation criteria. In time, this exercise will produce an application and admissions process.

Methods and variables

Caution

Slashing Implementation

jail, unJail, and slash functions are not used currently as part of the slashing implementation.

validatorThreshold

It stores the maximum number of validators accepted by the system, also called slots.

AccountStateRoot

• For various accounting done on Heimdall for validators and delegator, account root is submitted while submitting the checkpoint.
• accRoot is used while claimRewards and unStakeClaim.

stake / stakeFor

StakeManager.sol

function stake(
    uint256 amount,
    uint256 heimdallFee,
    bool acceptDelegation,
    bytes calldata signerPubkey
) public;

function stakeFor(
    address user,
    uint256 amount,
    uint256 heimdallFee,
    bool acceptDelegation,
    bytes memory signerPubkey
) public;

• Allows anyone with amount (in MATIC tokens) greater than minDeposit, if currentValidatorSetSize is less then validatorThreshold.
• Must transfer amount+heimdallFee, puts validator into auction period for an auctionInterval (more in Auction section).
• updateTimeLine updates special timeline data structure, which keeps track of active validators and active stake for given epoch / checkpoint count.
• One unique NFT is minted on each new stake or stakeFor call, which can be transferred to anyone but can be owned 1:1 Ethereum address.
• acceptDelegation set to true if validators want to accept delegation, ValidatorShare contract is deployed for the validator.

unstake

• Remove validator from validator set in next epoch (only valid for current checkpoint once called unstake)
• Remove validator’s stake from timeline data structure, update count for validator’s exit epoch.
• If validator had delegation on, collect all rewards and lock delegation contract for new delegations.

unstakeClaim

function unstakeClaim(uint256 validatorId) public;

• After unstaking, validators are put into withdrawal period so that they can be slashed, if any fraud found after unstaking, for past frauds.
• Once WITHDRAWAL_DELAY period is served, validators can call this function and do settlement with stakeManager (get rewards if any, get staked tokens back, burn NFT, etc).

restake

function restake(uint256 validatorId, uint256 amount, bool stakeRewards) public;

• Allows validators to increase their stake by putting new amount or rewards or both.
• Must update timeline (amount) for active stake.

withdrawRewards

function withdrawRewards(uint256 validatorId) public;

This method allows validators to withdraw accumulated rewards, must consider getting rewards from delegation contract if validator accepts delegation.

updateSigner

function updateSigner(uint256 validatorId, bytes memory signerPubkey) public

This method allows validators to update signer address (which is used to validate blocks on Polygon blockchain and checkpoint signatures on stakeManager).

topUpForFee

function topUpForFee(uint256 validatorId, uint256 heimdallFee) public;

Validators can top-up their balance for Heimdall fee by invoking this method.

claimFee

function claimFee(
        uint256 validatorId,
        uint256 accumSlashedAmount,
        uint256 accumFeeAmount,
        uint256 index,
        bytes memory proof
    ) public;

This method is used to withdraw fees from Heimdall. accountStateRoot is updated on each checkpoint, so that validators can provide proof of inclusion in this root for account on Heimdall and withdraw fee.

Note that accountStateRoot is re-written to prevent exits on multiple checkpoints (for old root and save accounting on stakeManager). accumSlashedAmount is unused at the moment and will be used for slashing on Heimdall if needed.

StakingNFT

Standard ERC721 contract with few restrictions like one token per user and minted in sequential manner.

startAuction

function startAuction(
    uint256 validatorId, /**  auction for validator */
    uint256 amount /**  amount greater then old validator's stake */
    ) external;

In order to start a bid or bid higher on already running auction, this function is used. Auction period runs in cycles like (auctionPeriod--dynasty)--(auctionPeriod--dynasty)--(auctionPeriod--dynasty) so it must check for correct auction period.

perceivedStakeFactor is used to calculate exact factorold stake (note currently it is by default 1 WIP for picking the function). *Must check for auction from last auction period if any still going on** (one can choose to not call confirmAuction in order to get their capital out in the next auction). Normally continuous english auction is going on in a auctionPeriod.

confirmAuctionBid

function confirmAuctionBid(
        uint256 validatorId,
        uint256 heimdallFee, /** for new validator */
        bool acceptDelegation,
        bytes calldata signerPubkey
    ) external

• Must check that this is not an auctionPeriod.
• If last bidder is owner of validatorId, behaviour should be similar to restake.
• In second case unStake validatorId and add new user as validator from next checkpoint, for the new user behaviour should be similar to stake/stakeFor.

checkSignatures

function checkSignatures(
        uint256 blockInterval,
        bytes32 voteHash,
        bytes32 stateRoot,
        bytes memory sigs
    ) public;

• Writes are meant only for RootChain contract when submitting checkpoints
• voteHash on which all validators sign (BFT ⅔+1 agreement)
• This function validates only unique sigs and checks for ⅔+1 power has signed on checkpoint root (inclusion in voteHash verification in RootChain contract for all data) currentValidatorSetTotalStake provides current active stake.
• Rewards are distributed proportionally to validator’s stake. More on rewards in Rewards Distribution

isValidator

Checks if a given validator is active validator for the current epoch.

Timeline data structure

struct State {
    int256 amount;
    int256 stakerCount;
}

mapping(uint256 => State) public validatorState;

StakingInfo

Centralized logging contract for both validator and delegation events, includes few read only functions. You can check out the source code of the StakingInfo.sol contract on GitHub.

ValidatorShareFactory

A factory contract to deploy ValidatorShare contract for each validator who opt-in for delegation. You can check out the source code of the ValidatorShareFactory.sol contract on GitHub.

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Last update: January 17, 2024

Authors: avenbreaks