feat(blockchain): introducing validator size cap size

mod/chain-spec/pkg/chain/chain_spec.go

@@ -183,6 +183,10 @@ type Spec[
 	// GetCometBFTConfigForSlot retrieves the CometBFT config for a specific
 	// slot.
 	GetCometBFTConfigForSlot(slot SlotT) CometBFTConfigT
+
+	// GetValidatorSetCap retrieves the maximum number of validators
+	// allowed in the active set.
+	GetValidatorsSetCapSize() uint32
 }
 
 // chainSpec is a concrete implementation of the ChainSpec interface, holding
@@ -476,3 +480,11 @@ func (c chainSpec[
 ]) GetCometBFTConfigForSlot(_ SlotT) CometBFTConfigT {
 	return c.Data.CometValues
 }
+
+// GetValidatorSetCap retrieves the maximum number of validators
+// allowed in the active set.
+func (c chainSpec[
+	DomainTypeT, EpochT, ExecutionAddressT, SlotT, CometBFTConfigT,
+]) GetValidatorsSetCapSize() uint32 {
+	return c.Data.ValidatorSetCapSize
+}

mod/chain-spec/pkg/chain/data.go

@@ -146,4 +146,7 @@ type SpecData[
 
 	// CometValues
 	CometValues CometBFTConfigT `mapstructure:"comet-bft-config"`
+
+	// Validators Set config
+	ValidatorSetCapSize uint32 `mapstructure:"validator-set-cap-size"`
 }

mod/config/pkg/spec/testnet.go

@@ -123,5 +123,6 @@ func BaseSpec() chain.SpecData[
 		BytesPerBlob:                     131072,
 		KZGCommitmentInclusionProofDepth: 17,
 		CometValues:                      cmtConsensusParams,
+		ValidatorSetCapSize:              256,
 	}
 }

mod/consensus-types/pkg/types/validator.go

@@ -313,6 +313,11 @@ func (v *Validator) SetEffectiveBalance(balance math.Gwei) {
 	v.EffectiveBalance = balance
 }
 
+// SetWithdrawableEpoch sets the epoch when the validator can withdraw.
+func (v *Validator) SetWithdrawableEpoch(e math.Epoch) {
+	v.WithdrawableEpoch = e
+}
+
 // GetWithdrawableEpoch returns the epoch when the validator can withdraw.
 func (v Validator) GetWithdrawableEpoch() math.Epoch {
 	return v.WithdrawableEpoch

mod/state-transition/pkg/core/errors.go

@@ -23,6 +23,10 @@ package core
 import "github.com/berachain/beacon-kit/mod/errors"
 
 var (
+	// ErrValidatorSetCapHit is returned when we try and add a validator
+	// that would breach validator set size cap.
+	ErrHitValidatorsSetCap = errors.New("hit validator set size cap")
+
 	// ErrBlockSlotTooLow is returned when the block slot is too low.
 	ErrBlockSlotTooLow = errors.New("block slot too low")
 

mod/state-transition/pkg/core/state_processor.go

@@ -282,22 +282,15 @@ func (sp *StateProcessor[
 	st BeaconStateT,
 	blk BeaconBlockT,
 ) error {
-	// process the freshly created header.
 	if err := sp.processBlockHeader(st, blk); err != nil {
 		return err
 	}
 
-	// process the execution payload.
-	if err := sp.processExecutionPayload(
-		ctx, st, blk,
-	); err != nil {
+	if err := sp.processExecutionPayload(ctx, st, blk); err != nil {
 		return err
 	}
 
-	// process the withdrawals.
-	if err := sp.processWithdrawals(
-		st, blk.GetBody(),
-	); err != nil {
+	if err := sp.processWithdrawals(st, blk.GetBody()); err != nil {
 		return err
 	}
 

mod/state-transition/pkg/core/state_processor_genesis.go

@@ -21,6 +21,8 @@
 package core
 
 import (
+	"fmt"
+
 	"github.com/berachain/beacon-kit/mod/primitives/pkg/common"
 	"github.com/berachain/beacon-kit/mod/primitives/pkg/constants"
 	"github.com/berachain/beacon-kit/mod/primitives/pkg/encoding/hex"
@@ -106,6 +108,17 @@ func (sp *StateProcessor[
 		}
 	}
 
+	// BeaconKit enforces a cap on the validator set size.
+	// If genesis deposits breaches the cap we return an error.
+	//#nosec:G701 // can't overflow.
+	if uint32(len(deposits)) > sp.cs.GetValidatorsSetCapSize() {
+		return nil, fmt.Errorf("validator set cap %d, deposits count %d: %w",
+			sp.cs.GetValidatorsSetCapSize(),
+			len(deposits),
+			ErrHitValidatorsSetCap,
+		)
+	}
+
 	for _, deposit := range deposits {
 		if err := sp.processDeposit(st, deposit); err != nil {
 			return nil, err

mod/state-transition/pkg/core/state_processor_staking.go

@@ -196,12 +196,35 @@ func (sp *StateProcessor[
 		math.Gwei(sp.cs.MaxEffectiveBalance()),
 	)
 
-	// TODO: This is a bug that lives on bArtio. Delete this eventually.
-	if sp.cs.DepositEth1ChainID() == bArtioChainID {
-		if err := st.AddValidatorBartio(val); err != nil {
+	if !sp.processingGenesis {
+		// BeaconKit enforces a cap on the validator set size. If a deposit is made
+		// that would breach the cap, we mark the validator as immediately
+		// withdrawable, so that it will be evicted in the next block along with
+		// the amount deposited.
+		validators, err := st.GetValidators()
+		if err != nil {
 			return err
 		}
-	} else if err := st.AddValidator(val); err != nil {
+
+		//#nosec:G701 // can't overflow.
+		if uint32(len(validators)) >= sp.cs.GetValidatorsSetCapSize() {
+			var slot math.Slot
+			slot, err = st.GetSlot()
+			if err != nil {
+				return err
+			}
+
+			epoch := sp.cs.SlotToEpoch(slot)
+			val.SetWithdrawableEpoch(epoch)
+		}
+	}
+
+	// TODO: This is a bug that lives on bArtio. Delete this eventually.
+	if sp.cs.DepositEth1ChainID() == bArtioChainID {
+		return st.AddValidatorBartio(val)
+	}
+
+	if err := st.AddValidator(val); err != nil {
 		return err
 	}