prysm-pulse/beacon-chain/core/state/transition.go

// Package state implements the whole state transition
// function which consists of per slot, per-epoch transitions.
// It also bootstraps the genesis beacon state for slot 0.
package state

import (
	"fmt"

	bal "github.com/prysmaticlabs/prysm/beacon-chain/core/balances"
	b "github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
	e "github.com/prysmaticlabs/prysm/beacon-chain/core/epoch"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
	v "github.com/prysmaticlabs/prysm/beacon-chain/core/validators"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	"github.com/sirupsen/logrus"
)

var log = logrus.WithField("prefix", "core/state")

// ExecuteStateTransition defines the procedure for a state transition function.
// Spec:
//  We now define the state transition function. At a high level the state transition is made up of three parts:
//  - The per-slot transitions, which happens at the start of every slot.
//  - The per-block transitions, which happens at every block.
//  - The per-epoch transitions, which happens at the end of the last slot of every epoch (i.e. (state.slot + 1) % SLOTS_PER_EPOCH == 0).
//  The per-slot transitions focus on the slot counter and block roots records updates.
//  The per-block transitions focus on verifying aggregate signatures and saving temporary records relating to the per-block activity in the state.
//  The per-epoch transitions focus on the validator registry, including adjusting balances and activating and exiting validators,
//  as well as processing crosslinks and managing block justification/finalization.
func ExecuteStateTransition(
	state *pb.BeaconState,
	block *pb.BeaconBlock,
	headRoot [32]byte,
	verifySignatures bool,
) (*pb.BeaconState, error) {
	var err error

	// Execute per slot transition.
	state = ProcessSlot(state, headRoot)

	// Execute per block transition.
	if block != nil {
		state, err = ProcessBlock(state, block, verifySignatures)
		if err != nil {
			return nil, fmt.Errorf("could not process block: %v", err)
		}
	}

	// Execute per epoch transition.
	if e.CanProcessEpoch(state) {
		state, err = ProcessEpoch(state)
	}
	if err != nil {
		return nil, fmt.Errorf("could not process epoch: %v", err)
	}

	return state, nil
}

// ProcessSlot happens every slot and focuses on the slot counter and block roots record updates.
// It happens regardless if there's an incoming block or not.
//
// Spec pseudocode definition:
//	Set state.slot += 1
//	Let previous_block_root be the hash_tree_root of the previous beacon block processed in the chain
//	Set state.latest_block_roots[(state.slot - 1) % LATEST_BLOCK_ROOTS_LENGTH] = previous_block_root
//	If state.slot % LATEST_BLOCK_ROOTS_LENGTH == 0
//		append merkle_root(state.latest_block_roots) to state.batched_block_roots
func ProcessSlot(state *pb.BeaconState, headRoot [32]byte) *pb.BeaconState {
	state.Slot++
	state = b.ProcessBlockRoots(state, headRoot)
	log.Info("Slot transition successfully processed slot %d", state.Slot)
	return state
}

// ProcessBlock creates a new, modified beacon state by applying block operation
// transformations as defined in the Ethereum Serenity specification, including processing proposer slashings,
// processing block attestations, and more.
func ProcessBlock(state *pb.BeaconState, block *pb.BeaconBlock, verifySignatures bool) (*pb.BeaconState, error) {
	if block.Slot != state.Slot {
		return nil, fmt.Errorf(
			"block.slot != state.slot, block.slot = %d, state.slot = %d",
			block.Slot,
			state.Slot,
		)
	}
	if verifySignatures {
		// TODO(#781): Verify Proposer Signature.
		if err := b.VerifyProposerSignature(block); err != nil {
			return nil, fmt.Errorf("could not verify proposer signature: %v", err)
		}
	}
	var err error
	state, err = b.ProcessBlockRandao(state, block)
	if err != nil {
		return nil, fmt.Errorf("could not verify and process block randao: %v", err)
	}
	state, err = b.ProcessProposerSlashings(state, block, verifySignatures)
	if err != nil {
		return nil, fmt.Errorf("could not verify block proposer slashings: %v", err)
	}
	state = b.ProcessEth1Data(state, block)
	state, err = b.ProcessAttesterSlashings(state, block, verifySignatures)
	if err != nil {
		return nil, fmt.Errorf("could not verify block attester slashings: %v", err)
	}
	state, err = b.ProcessBlockAttestations(state, block, verifySignatures)
	if err != nil {
		return nil, fmt.Errorf("could not process block attestations: %v", err)
	}
	state, err = b.ProcessValidatorDeposits(state, block)
	if err != nil {
		return nil, fmt.Errorf("could not process block validator deposits: %v", err)
	}
	state, err = b.ProcessValidatorExits(state, block, verifySignatures)
	if err != nil {
		return nil, fmt.Errorf("could not process validator exits: %v", err)
	}
	log.Info("Block transition successfully processed slot %d", state.Slot)
	return state, nil
}

// ProcessEpoch describes the per epoch operations that are performed on the
// beacon state.
//
// Spec pseudocode definition:
// 	 process_candidate_receipt_roots(state)
// 	 update_justification(state)
// 	 update_finalization(state)
// 	 update_crosslinks(state)
// 	 process_attester_reward_penalties(state)
// 	 process_crosslink_reward_penalties(state)
// 	 update_validator_registry(state)
// 	 final_book_keeping(state)
func ProcessEpoch(state *pb.BeaconState) (*pb.BeaconState, error) {
	// Calculate total balances of active validators of the current state.
	currentEpoch := helpers.CurrentEpoch(state)
	activeValidatorIndices := helpers.ActiveValidatorIndices(state.ValidatorRegistry, currentEpoch)
	totalBalance := e.TotalBalance(state, activeValidatorIndices)

	// Calculate the attesting balances of validators that justified the
	// epoch boundary block at the start of the current epoch.
	currentAttestations := e.CurrentAttestations(state)
	currentBoundaryAttestations, err := e.CurrentBoundaryAttestations(state, currentAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get current boundary attestations: %v", err)
	}
	currentBoundaryAttesterIndices, err := v.ValidatorIndices(state, currentBoundaryAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get current boundary attester indices: %v", err)
	}
	currentBoundaryAttestingBalances := e.TotalBalance(state, currentBoundaryAttesterIndices)

	// Calculate the attesting balances of validators that made an attestation
	// during previous epoch.
	prevEpochAttestations := e.PrevAttestations(state)
	prevAttesterIndices, err := v.ValidatorIndices(state, prevEpochAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev epoch attester indices: %v", err)
	}

	// Calculate the attesting balances of validators that targeted
	// previous justified hash.
	prevEpochJustifiedAttestations := e.PrevJustifiedAttestations(state,
		currentAttestations, prevEpochAttestations)

	prevEpochJustifiedAttesterIndices, err := v.ValidatorIndices(state, prevEpochJustifiedAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev epoch justified attester indices: %v", err)
	}
	prevEpochJustifiedAttestingBalance := e.TotalBalance(state, prevEpochJustifiedAttesterIndices)

	// Calculate the attesting balances of validator justifying epoch boundary block
	// at the start of previous epoch.
	prevEpochBoundaryAttestations, err := e.PrevBoundaryAttestations(state, prevEpochJustifiedAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev boundary attestations: %v", err)
	}
	prevEpochBoundaryAttesterIndices, err := v.ValidatorIndices(state, prevEpochBoundaryAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev boundary attester indices: %v", err)
	}
	prevEpochBoundaryAttestingBalances := e.TotalBalance(state, prevEpochBoundaryAttesterIndices)

	// Calculate attesting balances of validator attesting to expected beacon chain head
	// during previous epoch.
	prevEpochHeadAttestations, err := e.PrevHeadAttestations(state, prevEpochAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev head attestations: %v", err)
	}
	prevEpochHeadAttesterIndices, err := v.ValidatorIndices(state, prevEpochHeadAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not get prev head attester indices: %v", err)
	}
	prevEpochHeadAttestingBalances := e.TotalBalance(state, prevEpochHeadAttesterIndices)

	// Process eth1 data
	if e.CanProcessEth1Data(state) {
		state = e.ProcessEth1Data(state)
	}

	// Update justification.
	state = e.ProcessJustification(
		state,
		currentBoundaryAttestingBalances,
		prevEpochBoundaryAttestingBalances,
		totalBalance)

	// Update Finalization.
	state = e.ProcessFinalization(state)

	// Process crosslinks records.
	state, err = e.ProcessCrosslinks(
		state,
		currentAttestations,
		prevEpochAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not process crosslink records: %v", err)
	}

	// Process attester rewards and penalties.
	epochsSinceFinality := e.SinceFinality(state)
	switch {
	case epochsSinceFinality <= 4:
		// Apply rewards/penalties to validators for attesting
		// expected FFG source.
		state = bal.ExpectedFFGSource(
			state,
			prevEpochJustifiedAttesterIndices,
			prevEpochJustifiedAttestingBalance,
			totalBalance)
		// Apply rewards/penalties to validators for attesting
		// expected FFG target.
		state = bal.ExpectedFFGTarget(
			state,
			prevEpochBoundaryAttesterIndices,
			prevEpochBoundaryAttestingBalances,
			totalBalance)
		// Apply rewards/penalties to validators for attesting
		// expected beacon chain head.
		state = bal.ExpectedBeaconChainHead(
			state,
			prevEpochHeadAttesterIndices,
			prevEpochHeadAttestingBalances,
			totalBalance)
		// Apply rewards for to validators for including attestations
		// based on inclusion distance.
		state, err = bal.InclusionDistance(
			state,
			prevAttesterIndices,
			totalBalance)
		if err != nil {
			return nil, fmt.Errorf("could not calculate inclusion dist rewards: %v", err)
		}

	case epochsSinceFinality > 4:
		// Apply penalties for long inactive FFG source participants.
		state = bal.InactivityFFGSource(
			state,
			prevEpochJustifiedAttesterIndices,
			totalBalance,
			epochsSinceFinality)
		// Apply penalties for long inactive FFG target participants.
		state = bal.InactivityFFGTarget(
			state,
			prevEpochBoundaryAttesterIndices,
			totalBalance,
			epochsSinceFinality)
		// Apply penalties for long inactive validators who didn't
		// attest to head canonical chain.
		state = bal.InactivityChainHead(
			state,
			prevEpochHeadAttesterIndices,
			totalBalance)
		// Apply penalties for long inactive validators who also
		// exited with penalties.
		state = bal.InactivityExitedPenalties(
			state,
			totalBalance,
			epochsSinceFinality)
		// Apply penalties for long inactive validators that
		// don't include attestations.
		state, err = bal.InactivityInclusionDistance(
			state,
			prevAttesterIndices,
			totalBalance)
		if err != nil {
			return nil, fmt.Errorf("could not calculate inclusion penalties: %v", err)
		}
	}

	// Process Attestation Inclusion Rewards.
	state, err = bal.AttestationInclusion(
		state,
		totalBalance,
		prevAttesterIndices)
	if err != nil {
		return nil, fmt.Errorf("could not process attestation inclusion rewards: %v", err)
	}

	// Process crosslink rewards and penalties.
	state, err = bal.Crosslinks(
		state,
		currentAttestations,
		prevEpochAttestations)
	if err != nil {
		return nil, fmt.Errorf("could not process crosslink rewards and penalties: %v", err)
	}

	// Process ejections.
	state, err = e.ProcessEjections(state)
	if err != nil {
		return nil, fmt.Errorf("could not process ejections: %v", err)
	}

	// Process validator registry.
	state = e.ProcessPrevSlotShardSeed(state)
	state = v.ProcessPenaltiesAndExits(state)
	if e.CanProcessValidatorRegistry(state) {
		state, err = e.ProcessValidatorRegistry(state)
		if err != nil {
			return nil, fmt.Errorf("can not process validator registry: %v", err)
		}
	} else {
		state, err = e.ProcessPartialValidatorRegistry(state)
		if err != nil {
			return nil, fmt.Errorf("could not process partial validator registry: %v", err)
		}
	}

	// Final housekeeping updates.
	// Update index roots from current epoch to next epoch.
	state, err = e.UpdateLatestActiveIndexRoots(state)
	if err != nil {
		return nil, fmt.Errorf("could not update latest index roots: %v", err)
	}

	// Update accumulated slashed balances from current epoch to next epoch.
	state = e.UpdateLatestSlashedBalances(state)

	// Update current epoch's randao seed to next epoch.
	state, err = e.UpdateLatestRandaoMixes(state)
	if err != nil {
		return nil, fmt.Errorf("could not update latest randao mixes: %v", err)
	}

	// Clean up processed attestations.
	state = e.CleanupAttestations(state)
	log.Info("Epoch transition successfully processed slot %d", state.Slot)
	return state, nil
}