Add min commission rate logic (#3715)

* Add min commission rate logic

core/evm.go

@@ -19,6 +19,8 @@ package core
 import (
 	"math/big"
 
+	"github.com/harmony-one/harmony/internal/params"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/harmony-one/harmony/block"
 	consensus_engine "github.com/harmony-one/harmony/consensus/engine"
@@ -44,6 +46,9 @@ type ChainContext interface {
 
 	// ReadValidatorList returns the list of all validators
 	ReadValidatorList() ([]common.Address, error)
+
+	// Config returns chain config
+	Config() *params.ChainConfig
 }
 
 // NewEVMContext creates a new context for use in the EVM.

core/staking_verifier.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"math/big"
 
+	"github.com/harmony-one/harmony/staking/availability"
+
 	"github.com/harmony-one/harmony/internal/params"
 
 	"github.com/harmony-one/harmony/crypto/bls"
@@ -166,6 +168,14 @@ func VerifyAndEditValidatorFromMsg(
 		return nil, errCommissionRateChangeTooHigh
 	}
 
+	if chainContext.Config().IsMinCommissionRate(epoch) && newRate.LT(availability.MinCommissionRate) {
+		firstEpoch := stateDB.GetValidatorFirstElectionEpoch(msg.ValidatorAddress)
+		promoPeriod := chainContext.Config().MinCommissionPromoPeriod.Int64()
+		if firstEpoch.Uint64() != 0 && big.NewInt(0).Sub(epoch, firstEpoch).Int64() >= promoPeriod {
+			return nil, errCommissionRateChangeTooLow
+		}
+	}
+
 	snapshotValidator, err := chainContext.ReadValidatorSnapshot(wrapper.Address)
 	if err != nil {
 		return nil, errors.WithMessage(err, "validator snapshot not found.")

core/staking_verifier_test.go

@@ -55,8 +55,10 @@ var (
 	hundredKOnes    = new(big.Int).Mul(big.NewInt(100000), oneBig)
 
 	negRate           = numeric.NewDecWithPrec(-1, 10)
+	pointZeroOneDec   = numeric.NewDecWithPrec(1, 2)
 	pointOneDec       = numeric.NewDecWithPrec(1, 1)
 	pointTwoDec       = numeric.NewDecWithPrec(2, 1)
+	pointFourDec      = numeric.NewDecWithPrec(4, 1)
 	pointFiveDec      = numeric.NewDecWithPrec(5, 1)
 	pointSevenDec     = numeric.NewDecWithPrec(7, 1)
 	pointEightFiveDec = numeric.NewDecWithPrec(85, 2)
@@ -465,7 +467,7 @@ func TestVerifyAndEditValidatorFromMsg(t *testing.T) {
 			expWrapper: func() staking.ValidatorWrapper {
 				vw := defaultExpWrapperEditValidator()
 				vw.UpdateHeight = big.NewInt(defaultSnapBlockNumber)
-				vw.Rate = pointFiveDec
+				vw.Rate = pointFourDec
 				return vw
 			}(),
 		},
@@ -655,6 +657,51 @@ func TestVerifyAndEditValidatorFromMsg(t *testing.T) {
 
 			expErr: errors.New("banned status"),
 		},
+		{
+			// 14: Rate is lower than min rate of 5%
+			sdb: makeStateDBForStake(t),
+			bc: func() *fakeChainContext {
+				chain := makeFakeChainContextForStake()
+				vw := chain.vWrappers[validatorAddr]
+				vw.Rate = pointFourDec
+				chain.vWrappers[validatorAddr] = vw
+				return chain
+			}(),
+			epoch:    big.NewInt(20),
+			blockNum: big.NewInt(defaultBlockNumber),
+			msg: func() staking.EditValidator {
+				msg := defaultMsgEditValidator()
+				msg.CommissionRate = &pointZeroOneDec
+				return msg
+			}(),
+
+			expErr: errCommissionRateChangeTooLow,
+		},
+		{
+			// 15: Rate is ok within the promo period
+			sdb: makeStateDBForStake(t),
+			bc: func() *fakeChainContext {
+				chain := makeFakeChainContextForStake()
+				vw := chain.vWrappers[validatorAddr]
+				vw.Rate = pointFourDec
+				chain.vWrappers[validatorAddr] = vw
+				return chain
+			}(),
+			epoch:    big.NewInt(15),
+			blockNum: big.NewInt(defaultBlockNumber),
+			msg: func() staking.EditValidator {
+				msg := defaultMsgEditValidator()
+				msg.CommissionRate = &pointZeroOneDec
+				return msg
+			}(),
+
+			expWrapper: func() staking.ValidatorWrapper {
+				vw := defaultExpWrapperEditValidator()
+				vw.UpdateHeight = big.NewInt(defaultBlockNumber)
+				vw.Rate = pointZeroOneDec
+				return vw
+			}(),
+		},
 	}
 	for i, test := range tests {
 		w, err := VerifyAndEditValidatorFromMsg(test.sdb, test.bc, test.epoch, test.blockNum,
@@ -1588,6 +1635,7 @@ func updateStateValidators(sdb *state.DB, ws []*staking.ValidatorWrapper) error
 	for i, w := range ws {
 		sdb.SetValidatorFlag(w.Address)
 		sdb.AddBalance(w.Address, hundredKOnes)
+		sdb.SetValidatorFirstElectionEpoch(w.Address, big.NewInt(10))
 		if err := sdb.UpdateValidatorWrapper(w.Address, w); err != nil {
 			return fmt.Errorf("update %v vw error: %v", i, err)
 		}
@@ -1675,6 +1723,13 @@ func (chain *fakeChainContext) Engine() consensus_engine.Engine {
 	return nil
 }
 
+func (chain *fakeChainContext) Config() *params.ChainConfig {
+	config := &params.ChainConfig{}
+	config.MinCommissionRateEpoch = big.NewInt(0)
+	config.MinCommissionPromoPeriod = big.NewInt(10)
+	return config
+}
+
 func (chain *fakeChainContext) GetHeader(common.Hash, uint64) *block.Header {
 	return nil
 }
@@ -1709,6 +1764,12 @@ func (chain *fakeErrChainContext) GetHeader(common.Hash, uint64) *block.Header {
 	return nil
 }
 
+func (chain *fakeErrChainContext) Config() *params.ChainConfig {
+	config := &params.ChainConfig{}
+	config.MinCommissionRateEpoch = big.NewInt(10)
+	return config
+}
+
 func (chain *fakeErrChainContext) ReadDelegationsByDelegator(common.Address) (staking.DelegationIndexes, error) {
 	return nil, nil
 }

core/state/statedb.go

@@ -859,6 +859,23 @@ func (db *DB) UpdateValidatorWrapper(
 	return nil
 }
 
+// SetValidatorFirstElectionEpoch sets the epoch when the validator is first elected
+func (db *DB) SetValidatorFirstElectionEpoch(addr common.Address, epoch *big.Int) {
+	firstEpoch := db.GetValidatorFirstElectionEpoch(addr)
+	if firstEpoch.Uint64() == 0 {
+		// Set only when it's not set (or it's 0)
+		bytes := common.BigToHash(epoch)
+		db.SetState(addr, staking.FirstElectionEpochKey, bytes)
+	}
+}
+
+// GetValidatorFirstElectionEpoch gets the epoch when the validator was first elected
+func (db *DB) GetValidatorFirstElectionEpoch(addr common.Address) *big.Int {
+	so := db.getStateObject(addr)
+	value := so.GetState(db.db, staking.FirstElectionEpochKey)
+	return value.Big()
+}
+
 // SetValidatorFlag checks whether it is a validator object
 func (db *DB) SetValidatorFlag(addr common.Address) {
 	db.SetState(addr, staking.IsValidatorKey, staking.IsValidator)

core/state_transition.go

@@ -43,6 +43,7 @@ var (
 	errNoDelegationToUndelegate    = errors.New("no delegation to undelegate")
 	errCommissionRateChangeTooFast = errors.New("change on commission rate can not be more than max change rate within the same epoch")
 	errCommissionRateChangeTooHigh = errors.New("commission rate can not be higher than maximum commission rate")
+	errCommissionRateChangeTooLow  = errors.New("commission rate can not be lower than min rate of 5%")
 	errNoRewardsToCollect          = errors.New("no rewards to collect")
 	errNegativeAmount              = errors.New("amount can not be negative")
 	errDupIdentity                 = errors.New("validator identity exists")

core/vm/interface.go

@@ -47,6 +47,7 @@ type StateDB interface {
 	SetValidatorFlag(common.Address)
 	UnsetValidatorFlag(common.Address)
 	IsValidator(common.Address) bool
+	GetValidatorFirstElectionEpoch(addr common.Address) *big.Int
 	AddReward(*staking.ValidatorWrapper, *big.Int, map[common.Address]numeric.Dec) error
 
 	AddRefund(uint64)

internal/chain/engine.go

@@ -5,6 +5,8 @@ import (
 	"math/big"
 	"sort"
 
+	"github.com/harmony-one/harmony/internal/params"
+
 	bls2 "github.com/harmony-one/bls/ffi/go/bls"
 	blsvrf "github.com/harmony-one/harmony/crypto/vrf/bls"
 
@@ -290,7 +292,7 @@ func (e *engineImpl) Finalize(
 
 		// Needs to be after payoutUndelegations because payoutUndelegations
 		// depends on the old LastEpochInCommittee
-		if err := setLastEpochInCommittee(header, state); err != nil {
+		if err := setElectionEpochAndMinFee(header, state, chain.Config()); err != nil {
 			return nil, nil, err
 		}
 
@@ -392,7 +394,7 @@ func IsCommitteeSelectionBlock(chain engine.ChainReader, header *block.Header) b
 	return isBeaconChain && header.IsLastBlockInEpoch() && inPreStakingEra
 }
 
-func setLastEpochInCommittee(header *block.Header, state *state.DB) error {
+func setElectionEpochAndMinFee(header *block.Header, state *state.DB, config *params.ChainConfig) error {
 	newShardState, err := header.GetShardState()
 	if err != nil {
 		const msg = "[Finalize] failed to read shard state"
@@ -405,7 +407,20 @@ func setLastEpochInCommittee(header *block.Header, state *state.DB) error {
 				"[Finalize] failed to get validator from state to finalize",
 			)
 		}
+		// Set last epoch in committee
 		wrapper.LastEpochInCommittee = newShardState.Epoch
+
+		if config.IsMinCommissionRate(newShardState.Epoch) {
+			// Set first election epoch
+			state.SetValidatorFirstElectionEpoch(addr, newShardState.Epoch)
+
+			// Update minimum commission fee
+			if err := availability.UpdateMinimumCommissionFee(
+				newShardState.Epoch, state, addr, config.MinCommissionPromoPeriod.Int64(),
+			); err != nil {
+				return err
+			}
+		}
 	}
 	return nil
 }

internal/params/config.go

@@ -52,6 +52,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(530), // Around Monday Apr 12th 2021, 22:30 UTC
 		VRFEpoch:                   EpochTBD,
 		MinDelegation100Epoch:      EpochTBD,
+		MinCommissionRateEpoch:     EpochTBD,
+		MinCommissionPromoPeriod:   big.NewInt(100),
 		EPoSBound35Epoch:           EpochTBD,
 		EIP155Epoch:                big.NewInt(28),
 		S3Epoch:                    big.NewInt(28),
@@ -77,6 +79,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(73580),
 		VRFEpoch:                   EpochTBD,
 		MinDelegation100Epoch:      EpochTBD,
+		MinCommissionRateEpoch:     EpochTBD,
+		MinCommissionPromoPeriod:   big.NewInt(10),
 		EPoSBound35Epoch:           EpochTBD,
 		EIP155Epoch:                big.NewInt(0),
 		S3Epoch:                    big.NewInt(0),
@@ -103,6 +107,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(0),
 		VRFEpoch:                   big.NewInt(0),
 		MinDelegation100Epoch:      big.NewInt(0),
+		MinCommissionRateEpoch:     big.NewInt(0),
+		MinCommissionPromoPeriod:   big.NewInt(10),
 		EPoSBound35Epoch:           big.NewInt(0),
 		EIP155Epoch:                big.NewInt(0),
 		S3Epoch:                    big.NewInt(0),
@@ -129,6 +135,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(0),
 		VRFEpoch:                   big.NewInt(0),
 		MinDelegation100Epoch:      big.NewInt(0),
+		MinCommissionRateEpoch:     big.NewInt(0),
+		MinCommissionPromoPeriod:   big.NewInt(10),
 		EPoSBound35Epoch:           big.NewInt(0),
 		EIP155Epoch:                big.NewInt(0),
 		S3Epoch:                    big.NewInt(0),
@@ -155,6 +163,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(0),
 		VRFEpoch:                   big.NewInt(0),
 		MinDelegation100Epoch:      big.NewInt(0),
+		MinCommissionRateEpoch:     big.NewInt(0),
+		MinCommissionPromoPeriod:   big.NewInt(10),
 		EPoSBound35Epoch:           big.NewInt(0),
 		EIP155Epoch:                big.NewInt(0),
 		S3Epoch:                    big.NewInt(0),
@@ -180,6 +190,8 @@ var (
 		NoEarlyUnlockEpoch:         big.NewInt(0),
 		VRFEpoch:                   big.NewInt(0),
 		MinDelegation100Epoch:      big.NewInt(0),
+		MinCommissionRateEpoch:     big.NewInt(0),
+		MinCommissionPromoPeriod:   big.NewInt(10),
 		EPoSBound35Epoch:           big.NewInt(0),
 		EIP155Epoch:                big.NewInt(0),
 		S3Epoch:                    big.NewInt(0),
@@ -207,6 +219,8 @@ var (
 		big.NewInt(0),                      // NoEarlyUnlockEpoch
 		big.NewInt(0),                      // VRFEpoch
 		big.NewInt(0),                      // MinDelegation100Epoch
+		big.NewInt(0),                      // MinCommissionRateEpoch
+		big.NewInt(10),                     // MinCommissionPromoPeriod
 		big.NewInt(0),                      // EPoSBound35Epoch
 		big.NewInt(0),                      // EIP155Epoch
 		big.NewInt(0),                      // S3Epoch
@@ -234,6 +248,8 @@ var (
 		big.NewInt(0),        // NoEarlyUnlockEpoch
 		big.NewInt(0),        // VRFEpoch
 		big.NewInt(0),        // MinDelegation100Epoch
+		big.NewInt(0),        // MinCommissionRateEpoch
+		big.NewInt(10),       // MinCommissionPromoPeriod
 		big.NewInt(0),        // EPoSBound35Epoch
 		big.NewInt(0),        // EIP155Epoch
 		big.NewInt(0),        // S3Epoch
@@ -318,6 +334,12 @@ type ChainConfig struct {
 	// MinDelegation100Epoch is the epoch when min delegation is reduced from 1000 ONE to 100 ONE
 	MinDelegation100Epoch *big.Int `json:"min-delegation-100-epoch,omitempty"`
 
+	// MinCommissionRateEpoch is the epoch when policy for minimum comission rate of 5% is started
+	MinCommissionRateEpoch *big.Int `json:"min-commission-rate-epoch,omitempty"`
+
+	// MinCommissionPromoPeriod is the number of epochs when newly elected validators can have 0% commission
+	MinCommissionPromoPeriod *big.Int `json:"commission-promo-period,omitempty"`
+
 	// EPoSBound35Epoch is the epoch when the EPoS bound parameter c is changed from 15% to 35%
 	EPoSBound35Epoch *big.Int `json:"epos-bound-35-epoch,omitempty"`
 
@@ -417,6 +439,11 @@ func (c *ChainConfig) IsMinDelegation100(epoch *big.Int) bool {
 	return isForked(c.MinDelegation100Epoch, epoch)
 }
 
+// IsMinCommissionRate determines whether it is the epoch to start the policy of 5% min commission
+func (c *ChainConfig) IsMinCommissionRate(epoch *big.Int) bool {
+	return isForked(c.MinCommissionRateEpoch, epoch)
+}
+
 // IsEPoSBound35 determines whether it is the epoch to extend the EPoS bound to 35%
 func (c *ChainConfig) IsEPoSBound35(epoch *big.Int) bool {
 	return isForked(c.EPoSBound35Epoch, epoch)

staking/availability/measure.go

@@ -3,6 +3,8 @@ package availability
 import (
 	"math/big"
 
+	"github.com/harmony-one/harmony/core/state"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/harmony-one/harmony/crypto/bls"
 	"github.com/harmony-one/harmony/internal/utils"
@@ -15,6 +17,8 @@ import (
 
 var (
 	measure = numeric.NewDec(2).Quo(numeric.NewDec(3))
+
+	MinCommissionRate = numeric.MustNewDecFromStr("0.05")
 	// ErrDivByZero ..
 	ErrDivByZero = errors.New("toSign of availability cannot be 0, mistake in protocol")
 )
@@ -215,3 +219,34 @@ func ComputeAndMutateEPOSStatus(
 
 	return nil
 }
+
+// UpdateMinimumCommissionFee update the validator commission fee to the minimum 5%
+// if the validator has a lower commission rate and 100 epochs have passed after
+// the validator was first elected.
+func UpdateMinimumCommissionFee(
+	electionEpoch *big.Int,
+	state *state.DB,
+	addr common.Address,
+	promoPeriod int64,
+) error {
+	utils.Logger().Info().Msg("begin update min commission fee")
+
+	wrapper, err := state.ValidatorWrapper(addr)
+	if err != nil {
+		return err
+	}
+
+	firstElectionEpoch := state.GetValidatorFirstElectionEpoch(addr)
+
+	if firstElectionEpoch.Uint64() != 0 && big.NewInt(0).Sub(electionEpoch, firstElectionEpoch).Int64() >= int64(promoPeriod) {
+		if wrapper.Rate.LT(MinCommissionRate) {
+			utils.Logger().Info().
+				Str("addr", addr.Hex()).
+				Str("old rate", wrapper.Rate.String()).
+				Str("firstElectionEpoch", firstElectionEpoch.String()).
+				Msg("updating min commission rate")
+			wrapper.Rate.SetBytes(MinCommissionRate.Bytes())
+		}
+	}
+	return nil
+}

staking/params.go

@@ -9,6 +9,7 @@ const (
 	isValidatorStr        = "Harmony/IsValidator/Value/v1"
 	collectRewardsStr     = "Harmony/CollectRewards"
 	delegateStr           = "Harmony/Delegate"
+	firstElectionEpochStr = "Harmony/FirstElectionEpoch/Key/v1"
 )
 
 // keys used to retrieve staking related informatio
@@ -17,4 +18,5 @@ var (
 	IsValidator           = crypto.Keccak256Hash([]byte(isValidatorStr))
 	CollectRewardsTopic   = crypto.Keccak256Hash([]byte(collectRewardsStr))
 	DelegateTopic         = crypto.Keccak256Hash([]byte(delegateStr))
+	FirstElectionEpochKey = crypto.Keccak256Hash([]byte(firstElectionEpochStr))
 )

staking/types/test/prototype.go

@@ -59,9 +59,9 @@ var (
 	}
 
 	commissionRates = staking.CommissionRates{
-		Rate:          numeric.NewDecWithPrec(5, 1),
+		Rate:          numeric.NewDecWithPrec(4, 1),
 		MaxRate:       numeric.NewDecWithPrec(9, 1),
-		MaxChangeRate: numeric.NewDecWithPrec(3, 1),
+		MaxChangeRate: numeric.NewDecWithPrec(4, 1),
 	}
 
 	commission = staking.Commission{