Unrealized justification (#10659)

* unrealized justification API

* Add time elapse logging

* add unrealized justification checkpoint

* Use UnrealizedJustificationCheckpoint

* Refactor unrealized checkpoints

* Move logic to state package

* do not use ctx on a sum

* fix ctx

* add tests

* fix conflicts

* unhandled error

* Fix ordering in computing checkpoints

* gaz

* keep finalized checkpoint if nothing justified

* gaz

* copy checkpoint

* fix check for nil

* Add state package tests

* Add tests

* Radek's review

* add more tests

* Update beacon-chain/core/epoch/precompute/justification_finalization.go

Co-authored-by: terencechain <terence@prysmaticlabs.com>

* deduplicate to stateutil

* missing file

* Add stateutil test

* Minor refactor, don't export certain things

* Fix exports in tests

* remove unused error

Co-authored-by: terence tsao <terence@prysmaticlabs.com>
Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

beacon-chain/core/altair/epoch_precompute.go

@@ -47,7 +47,7 @@ func InitializePrecomputeValidators(ctx context.Context, beaconState state.Beaco
 				return err
 			}
 		}
-		// Set validator's active status for preivous epoch.
+		// Set validator's active status for previous epoch.
 		if helpers.IsActiveValidatorUsingTrie(val, prevEpoch) {
 			v.IsActivePrevEpoch = true
 			bal.ActivePrevEpoch, err = math.Add64(bal.ActivePrevEpoch, val.EffectiveBalance())

beacon-chain/core/epoch/precompute/BUILD.bazel

@@ -28,6 +28,7 @@ go_library(
         "//runtime/version:go_default_library",
         "//time/slots:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
+        "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
         "@io_opencensus_go//trace:go_default_library",
     ],
 )
@@ -43,11 +44,13 @@ go_test(
     ],
     embed = [":go_default_library"],
     deps = [
+        "//beacon-chain/core/altair:go_default_library",
         "//beacon-chain/core/epoch:go_default_library",
         "//beacon-chain/core/helpers:go_default_library",
         "//beacon-chain/core/time:go_default_library",
         "//beacon-chain/state:go_default_library",
         "//beacon-chain/state/v1:go_default_library",
+        "//beacon-chain/state/v2:go_default_library",
         "//config/fieldparams:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/primitives:go_default_library",

beacon-chain/core/epoch/precompute/justification_finalization.go

@@ -2,6 +2,7 @@ package precompute
 
 import (
 	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/go-bitfield"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/time"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
@@ -9,6 +10,24 @@ import (
 	"github.com/prysmaticlabs/prysm/time/slots"
 )
 
+var errNilState = errors.New("nil state")
+
+// UnrealizedCheckpoints returns the justification and finalization checkpoints of the
+// given state as if it was progressed with empty slots until the next epoch.
+func UnrealizedCheckpoints(st state.BeaconState) (*ethpb.Checkpoint, *ethpb.Checkpoint, error) {
+	if st == nil || st.IsNil() {
+		return nil, nil, errNilState
+	}
+
+	activeBalance, prevTarget, currentTarget, err := st.UnrealizedCheckpointBalances()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	justification := processJustificationBits(st, activeBalance, prevTarget, currentTarget)
+	return computeCheckpoints(st, justification)
+}
+
 // ProcessJustificationAndFinalizationPreCompute processes justification and finalization during
 // epoch processing. This is where a beacon node can justify and finalize a new epoch.
 // Note: this is an optimized version by passing in precomputed total and attesting balances.
@@ -34,12 +53,55 @@ func ProcessJustificationAndFinalizationPreCompute(state state.BeaconState, pBal
 		return state, nil
 	}
 
-	return weighJustificationAndFinalization(state, pBal.ActiveCurrentEpoch, pBal.PrevEpochTargetAttested, pBal.CurrentEpochTargetAttested)
+	newBits := processJustificationBits(state, pBal.ActiveCurrentEpoch, pBal.PrevEpochTargetAttested, pBal.CurrentEpochTargetAttested)
+
+	return weighJustificationAndFinalization(state, newBits)
 }
 
-// weighJustificationAndFinalization processes justification and finalization during
+// processJustificationBits processes the justification bits during epoch processing.
+func processJustificationBits(state state.BeaconState, totalActiveBalance, prevEpochTargetBalance, currEpochTargetBalance uint64) bitfield.Bitvector4 {
+	newBits := state.JustificationBits()
+	newBits.Shift(1)
+	// If 2/3 or more of total balance attested in the previous epoch.
+	if 3*prevEpochTargetBalance >= 2*totalActiveBalance {
+		newBits.SetBitAt(1, true)
+	}
+
+	if 3*currEpochTargetBalance >= 2*totalActiveBalance {
+		newBits.SetBitAt(0, true)
+	}
+
+	return newBits
+}
+
+// updateJustificationAndFinalization processes justification and finalization during
 // epoch processing. This is where a beacon node can justify and finalize a new epoch.
-//
+func weighJustificationAndFinalization(state state.BeaconState, newBits bitfield.Bitvector4) (state.BeaconState, error) {
+	jc, fc, err := computeCheckpoints(state, newBits)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := state.SetPreviousJustifiedCheckpoint(state.CurrentJustifiedCheckpoint()); err != nil {
+		return nil, err
+	}
+
+	if err := state.SetCurrentJustifiedCheckpoint(jc); err != nil {
+		return nil, err
+	}
+
+	if err := state.SetJustificationBits(newBits); err != nil {
+		return nil, err
+	}
+
+	if err := state.SetFinalizedCheckpoint(fc); err != nil {
+		return nil, err
+	}
+	return state, nil
+}
+
+// computeCheckpoints computes the new Justification and Finalization
+// checkpoints at epoch transition
 // Spec pseudocode definition:
 // def weigh_justification_and_finalization(state: BeaconState,
 //                                         total_active_balance: Gwei,
@@ -77,88 +139,57 @@ func ProcessJustificationAndFinalizationPreCompute(state state.BeaconState, pBal
 //    # The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source
 //    if all(bits[0:2]) and old_current_justified_checkpoint.epoch + 1 == current_epoch:
 //        state.finalized_checkpoint = old_current_justified_checkpoint
-func weighJustificationAndFinalization(state state.BeaconState,
+func computeCheckpoints(state state.BeaconState, newBits bitfield.Bitvector4) (*ethpb.Checkpoint, *ethpb.Checkpoint, error) {
-	totalActiveBalance, prevEpochTargetBalance, currEpochTargetBalance uint64) (state.BeaconState, error) {
 	prevEpoch := time.PrevEpoch(state)
 	currentEpoch := time.CurrentEpoch(state)
 	oldPrevJustifiedCheckpoint := state.PreviousJustifiedCheckpoint()
 	oldCurrJustifiedCheckpoint := state.CurrentJustifiedCheckpoint()
 
-	// Process justifications
+	justifiedCheckpoint := state.CurrentJustifiedCheckpoint()
-	if err := state.SetPreviousJustifiedCheckpoint(state.CurrentJustifiedCheckpoint()); err != nil {
+	finalizedCheckpoint := state.FinalizedCheckpoint()
-		return nil, err
-	}
-	newBits := state.JustificationBits()
-	newBits.Shift(1)
-	if err := state.SetJustificationBits(newBits); err != nil {
-		return nil, err
-	}
-
-	// Note: the spec refers to the bit index position starting at 1 instead of starting at zero.
-	// We will use that paradigm here for consistency with the godoc spec definition.
-
-	// If 2/3 or more of total balance attested in the previous epoch.
-	if 3*prevEpochTargetBalance >= 2*totalActiveBalance {
-		blockRoot, err := helpers.BlockRoot(state, prevEpoch)
-		if err != nil {
-			return nil, errors.Wrapf(err, "could not get block root for previous epoch %d", prevEpoch)
-		}
-		if err := state.SetCurrentJustifiedCheckpoint(&ethpb.Checkpoint{Epoch: prevEpoch, Root: blockRoot}); err != nil {
-			return nil, err
-		}
-		newBits = state.JustificationBits()
-		newBits.SetBitAt(1, true)
-		if err := state.SetJustificationBits(newBits); err != nil {
-			return nil, err
-		}
-	}
 
 	// If 2/3 or more of the total balance attested in the current epoch.
-	if 3*currEpochTargetBalance >= 2*totalActiveBalance {
+	if newBits.BitAt(0) {
 		blockRoot, err := helpers.BlockRoot(state, currentEpoch)
 		if err != nil {
-			return nil, errors.Wrapf(err, "could not get block root for current epoch %d", prevEpoch)
+			return nil, nil, errors.Wrapf(err, "could not get block root for current epoch %d", currentEpoch)
 		}
-		if err := state.SetCurrentJustifiedCheckpoint(&ethpb.Checkpoint{Epoch: currentEpoch, Root: blockRoot}); err != nil {
+		justifiedCheckpoint.Epoch = currentEpoch
-			return nil, err
+		justifiedCheckpoint.Root = blockRoot
-		}
+	} else if newBits.BitAt(1) {
-		newBits = state.JustificationBits()
+		// If 2/3 or more of total balance attested in the previous epoch.
-		newBits.SetBitAt(0, true)
+		blockRoot, err := helpers.BlockRoot(state, prevEpoch)
-		if err := state.SetJustificationBits(newBits); err != nil {
+		if err != nil {
-			return nil, err
+			return nil, nil, errors.Wrapf(err, "could not get block root for previous epoch %d", prevEpoch)
 		}
+		justifiedCheckpoint.Epoch = prevEpoch
+		justifiedCheckpoint.Root = blockRoot
 	}
 
 	// Process finalization according to Ethereum Beacon Chain specification.
-	justification := state.JustificationBits().Bytes()[0]
+	if len(newBits) == 0 {
+		return nil, nil, errors.New("empty justification bits")
+	}
+	justification := newBits.Bytes()[0]
 
 	// 2nd/3rd/4th (0b1110) most recent epochs are justified, the 2nd using the 4th as source.
 	if justification&0x0E == 0x0E && (oldPrevJustifiedCheckpoint.Epoch+3) == currentEpoch {
-		if err := state.SetFinalizedCheckpoint(oldPrevJustifiedCheckpoint); err != nil {
+		finalizedCheckpoint = oldPrevJustifiedCheckpoint
-			return nil, err
-		}
 	}
 
 	// 2nd/3rd (0b0110) most recent epochs are justified, the 2nd using the 3rd as source.
 	if justification&0x06 == 0x06 && (oldPrevJustifiedCheckpoint.Epoch+2) == currentEpoch {
-		if err := state.SetFinalizedCheckpoint(oldPrevJustifiedCheckpoint); err != nil {
+		finalizedCheckpoint = oldPrevJustifiedCheckpoint
-			return nil, err
-		}
 	}
 
 	// 1st/2nd/3rd (0b0111) most recent epochs are justified, the 1st using the 3rd as source.
 	if justification&0x07 == 0x07 && (oldCurrJustifiedCheckpoint.Epoch+2) == currentEpoch {
-		if err := state.SetFinalizedCheckpoint(oldCurrJustifiedCheckpoint); err != nil {
+		finalizedCheckpoint = oldCurrJustifiedCheckpoint
-			return nil, err
-		}
 	}
 
 	// The 1st/2nd (0b0011) most recent epochs are justified, the 1st using the 2nd as source
 	if justification&0x03 == 0x03 && (oldCurrJustifiedCheckpoint.Epoch+1) == currentEpoch {
-		if err := state.SetFinalizedCheckpoint(oldCurrJustifiedCheckpoint); err != nil {
+		finalizedCheckpoint = oldCurrJustifiedCheckpoint
-			return nil, err
-		}
 	}
-
+	return justifiedCheckpoint, finalizedCheckpoint, nil
-	return state, nil
 }

beacon-chain/core/epoch/precompute/justification_finalization_test.go

@@ -1,11 +1,14 @@
 package precompute_test
 
 import (
+	"context"
 	"testing"
 
 	"github.com/prysmaticlabs/go-bitfield"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/altair"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/epoch/precompute"
 	v1 "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
+	v2 "github.com/prysmaticlabs/prysm/beacon-chain/state/v2"
 	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
 	"github.com/prysmaticlabs/prysm/config/params"
 	types "github.com/prysmaticlabs/prysm/consensus-types/primitives"
@@ -123,3 +126,127 @@ func TestProcessJustificationAndFinalizationPreCompute_JustifyPrevEpoch(t *testi
 	assert.DeepEqual(t, params.BeaconConfig().ZeroHash[:], newState.FinalizedCheckpoint().Root)
 	assert.Equal(t, types.Epoch(0), newState.FinalizedCheckpointEpoch(), "Unexpected finalized epoch")
 }
+
+func TestUnrealizedCheckpoints(t *testing.T) {
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	balances := make([]uint64, len(validators))
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch:        params.BeaconConfig().FarFutureEpoch,
+			EffectiveBalance: params.BeaconConfig().MaxEffectiveBalance,
+		}
+		balances[i] = params.BeaconConfig().MaxEffectiveBalance
+	}
+	pjr := [32]byte{'p'}
+	cjr := [32]byte{'c'}
+	je := types.Epoch(3)
+	fe := types.Epoch(2)
+	pjcp := &ethpb.Checkpoint{Root: pjr[:], Epoch: fe}
+	cjcp := &ethpb.Checkpoint{Root: cjr[:], Epoch: je}
+	fcp := &ethpb.Checkpoint{Root: pjr[:], Epoch: fe}
+	tests := []struct {
+		name                                 string
+		slot                                 types.Slot
+		prevVals, currVals                   int
+		expectedJustified, expectedFinalized types.Epoch // The expected unrealized checkpoint epochs
+	}{
+		{
+			"Not enough votes, keep previous justification",
+			129,
+			len(validators) / 3,
+			len(validators) / 3,
+			je,
+			fe,
+		},
+		{
+			"Not enough votes, keep previous justification, N+2",
+			161,
+			len(validators) / 3,
+			len(validators) / 3,
+			je,
+			fe,
+		},
+		{
+			"Enough to justify previous epoch but not current",
+			129,
+			2*len(validators)/3 + 3,
+			len(validators) / 3,
+			je,
+			fe,
+		},
+		{
+			"Enough to justify previous epoch but not current, N+2",
+			161,
+			2*len(validators)/3 + 3,
+			len(validators) / 3,
+			je + 1,
+			fe,
+		},
+		{
+			"Enough to justify current epoch",
+			129,
+			len(validators) / 3,
+			2*len(validators)/3 + 3,
+			je + 1,
+			fe,
+		},
+		{
+			"Enough to justify current epoch, but not previous",
+			161,
+			len(validators) / 3,
+			2*len(validators)/3 + 3,
+			je + 2,
+			fe,
+		},
+		{
+			"Enough to justify current and previous",
+			161,
+			2*len(validators)/3 + 3,
+			2*len(validators)/3 + 3,
+			je + 2,
+			fe,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			base := &ethpb.BeaconStateAltair{
+				RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+
+				Validators:                  validators,
+				Slot:                        test.slot,
+				CurrentEpochParticipation:   make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+				PreviousEpochParticipation:  make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+				Balances:                    balances,
+				PreviousJustifiedCheckpoint: pjcp,
+				CurrentJustifiedCheckpoint:  cjcp,
+				FinalizedCheckpoint:         fcp,
+				InactivityScores:            make([]uint64, len(validators)),
+				JustificationBits:           make(bitfield.Bitvector4, 1),
+			}
+			for i := 0; i < test.prevVals; i++ {
+				base.PreviousEpochParticipation[i] = 0xFF
+			}
+			for i := 0; i < test.currVals; i++ {
+				base.CurrentEpochParticipation[i] = 0xFF
+			}
+			if test.slot > 130 {
+				base.JustificationBits.SetBitAt(2, true)
+				base.JustificationBits.SetBitAt(3, true)
+			} else {
+				base.JustificationBits.SetBitAt(1, true)
+				base.JustificationBits.SetBitAt(2, true)
+			}
+
+			state, err := v2.InitializeFromProto(base)
+			require.NoError(t, err)
+
+			_, _, err = altair.InitializePrecomputeValidators(context.Background(), state)
+			require.NoError(t, err)
+
+			jc, fc, err := precompute.UnrealizedCheckpoints(state)
+			require.NoError(t, err)
+			require.DeepEqual(t, test.expectedJustified, jc.Epoch)
+			require.DeepEqual(t, test.expectedFinalized, fc.Epoch)
+		})
+	}
+}

beacon-chain/state/interfaces.go

@@ -223,6 +223,7 @@ type FutureForkStub interface {
 	AppendInactivityScore(s uint64) error
 	CurrentEpochParticipation() ([]byte, error)
 	PreviousEpochParticipation() ([]byte, error)
+	UnrealizedCheckpointBalances() (uint64, uint64, uint64, error)
 	InactivityScores() ([]uint64, error)
 	SetInactivityScores(val []uint64) error
 	CurrentSyncCommittee() (*ethpb.SyncCommittee, error)

beacon-chain/state/state-native/BUILD.bazel

@@ -4,6 +4,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "doc.go",
+        "error.go",
         "getters_attestation.go",
         "getters_block.go",
         "getters_checkpoint.go",
@@ -54,6 +55,7 @@ go_library(
         "//tools/pcli:__pkg__",
     ],
     deps = [
+        "//beacon-chain/core/time:go_default_library",
         "//beacon-chain/state:go_default_library",
         "//beacon-chain/state/fieldtrie:go_default_library",
         "//beacon-chain/state/state-native/custom-types:go_default_library",
@@ -83,6 +85,7 @@ go_test(
         "getters_attestation_test.go",
         "getters_block_test.go",
         "getters_checkpoint_test.go",
+        "getters_participation_test.go",
         "getters_test.go",
         "getters_validator_test.go",
         "hasher_test.go",

beacon-chain/state/state-native/error.go

@@ -0,0 +1,5 @@
+package state_native
+
+import "errors"
+
+var ErrNilParticipation = errors.New("Nil epoch participation in state")

beacon-chain/state/state-native/getters_participation.go

@@ -1,6 +1,8 @@
 package state_native
 
 import (
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/time"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stateutil"
 	"github.com/prysmaticlabs/prysm/runtime/version"
 )
 
@@ -36,6 +38,28 @@ func (b *BeaconState) PreviousEpochParticipation() ([]byte, error) {
 	return b.previousEpochParticipationVal(), nil
 }
 
+// UnrealizedCheckpointBalances returns the total balances: active, target attested in
+// current epoch and target attested in previous epoch. This function is used to
+// compute the "unrealized justification" that a synced Beacon Block will have.
+func (b *BeaconState) UnrealizedCheckpointBalances() (uint64, uint64, uint64, error) {
+	if b.version == version.Phase0 {
+		return 0, 0, 0, errNotSupported("UnrealizedCheckpointBalances", b.version)
+	}
+
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	cp := b.currentEpochParticipation
+	pp := b.previousEpochParticipation
+	if cp == nil || pp == nil {
+		return 0, 0, 0, ErrNilParticipation
+	}
+
+	currentEpoch := time.CurrentEpoch(b)
+	return stateutil.UnrealizedCheckpointBalances(cp, pp, b.validators, currentEpoch)
+
+}
+
 // currentEpochParticipationVal corresponding to participation bits on the beacon chain.
 // This assumes that a lock is already held on BeaconState.
 func (b *BeaconState) currentEpochParticipationVal() []byte {

beacon-chain/state/state-native/getters_participation_test.go

@@ -0,0 +1,64 @@
+package state_native
+
+import (
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/config/params"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestState_UnrealizedCheckpointBalances(t *testing.T) {
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	balances := make([]uint64, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch:        params.BeaconConfig().FarFutureEpoch,
+			EffectiveBalance: params.BeaconConfig().MaxEffectiveBalance,
+		}
+		balances[i] = params.BeaconConfig().MaxEffectiveBalance
+	}
+	base := &ethpb.BeaconStateAltair{
+		Slot:        2,
+		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+
+		Validators:                 validators,
+		CurrentEpochParticipation:  make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		PreviousEpochParticipation: make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		Balances:                   balances,
+	}
+	state, err := InitializeFromProtoAltair(base)
+	require.NoError(t, err)
+
+	// No one voted in the last two epochs
+	allActive := params.BeaconConfig().MinGenesisActiveValidatorCount * params.BeaconConfig().MaxEffectiveBalance
+	active, previous, current, err := state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, uint64(0), previous)
+
+	// Add some votes in the last two epochs:
+	base.CurrentEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[1] = 0xFF
+
+	state, err = InitializeFromProtoAltair(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, current)
+	require.Equal(t, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+
+	// Slash some validators
+	validators[0].Slashed = true
+	state, err = InitializeFromProtoAltair(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive-params.BeaconConfig().MaxEffectiveBalance, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, previous)
+
+}

beacon-chain/state/stateutil/BUILD.bazel

@@ -15,6 +15,7 @@ go_library(
         "state_hasher.go",
         "sync_committee.root.go",
         "trie_helpers.go",
+        "unrealized_justification.go",
         "validator_map_handler.go",
         "validator_root.go",
     ],
@@ -57,6 +58,7 @@ go_test(
         "reference_bench_test.go",
         "state_root_test.go",
         "trie_helpers_test.go",
+        "unrealized_justification_test.go",
         "validator_root_test.go",
     ],
     embed = [":go_default_library"],

beacon-chain/state/stateutil/unrealized_justification.go

@@ -0,0 +1,43 @@
+package stateutil
+
+import (
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/config/params"
+	types "github.com/prysmaticlabs/prysm/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/math"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+)
+
+func UnrealizedCheckpointBalances(cp, pp []byte, validators []*ethpb.Validator, currentEpoch types.Epoch) (uint64, uint64, uint64, error) {
+	targetIdx := params.BeaconConfig().TimelyTargetFlagIndex
+	activeBalance := uint64(0)
+	currentTarget := uint64(0)
+	prevTarget := uint64(0)
+	if len(cp) < len(validators) || len(pp) < len(validators) {
+		return 0, 0, 0, errors.New("participation does not match validator set")
+	}
+
+	var err error
+	for i, v := range validators {
+		active := v.ActivationEpoch <= currentEpoch && currentEpoch < v.ExitEpoch
+		if active && !v.Slashed {
+			activeBalance, err = math.Add64(activeBalance, v.EffectiveBalance)
+			if err != nil {
+				return 0, 0, 0, err
+			}
+			if ((cp[i] >> targetIdx) & 1) == 1 {
+				currentTarget, err = math.Add64(currentTarget, v.EffectiveBalance)
+				if err != nil {
+					return 0, 0, 0, err
+				}
+			}
+			if ((pp[i] >> targetIdx) & 1) == 1 {
+				prevTarget, err = math.Add64(prevTarget, v.EffectiveBalance)
+				if err != nil {
+					return 0, 0, 0, err
+				}
+			}
+		}
+	}
+	return activeBalance, prevTarget, currentTarget, nil
+}

beacon-chain/state/stateutil/unrealized_justification_test.go

@@ -0,0 +1,95 @@
+package stateutil
+
+import (
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/config/params"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestState_UnrealizedCheckpointBalances(t *testing.T) {
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	targetFlag := params.BeaconConfig().TimelyTargetFlagIndex
+	expectedActive := params.BeaconConfig().MinGenesisActiveValidatorCount * params.BeaconConfig().MaxEffectiveBalance
+
+	balances := make([]uint64, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch:        params.BeaconConfig().FarFutureEpoch,
+			EffectiveBalance: params.BeaconConfig().MaxEffectiveBalance,
+		}
+		balances[i] = params.BeaconConfig().MaxEffectiveBalance
+	}
+	cp := make([]byte, len(validators))
+	pp := make([]byte, len(validators))
+
+	t.Run("No one voted last two epochs", func(tt *testing.T) {
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 0)
+		require.NoError(tt, err)
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, uint64(0), current)
+		require.Equal(tt, uint64(0), previous)
+	})
+
+	t.Run("bad votes in last two epochs", func(tt *testing.T) {
+		copy(cp, []byte{0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0x00})
+		copy(pp, []byte{0x00, 0x00, 0x00, 0x00})
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 1)
+		require.NoError(tt, err)
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, uint64(0), current)
+		require.Equal(tt, uint64(0), previous)
+	})
+
+	t.Run("two votes in last epoch", func(tt *testing.T) {
+		copy(cp, []byte{0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0x00, 1 << targetFlag, 1 << targetFlag})
+		copy(pp, []byte{0x00, 0x00, 0x00, 0x00, 0xFF ^ (1 << targetFlag)})
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 1)
+		require.NoError(tt, err)
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, 2*params.BeaconConfig().MaxEffectiveBalance, current)
+		require.Equal(tt, uint64(0), previous)
+	})
+
+	t.Run("two votes in previous epoch", func(tt *testing.T) {
+		copy(cp, []byte{0x00, 0x00, 0x00, 0x00, 0xFF ^ (1 << targetFlag), 0x00})
+		copy(pp, []byte{0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0x00, 1 << targetFlag, 1 << targetFlag})
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 1)
+		require.NoError(tt, err)
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, uint64(0), current)
+		require.Equal(tt, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+	})
+
+	t.Run("votes in both epochs, decreased balance in first validator", func(tt *testing.T) {
+		validators[0].EffectiveBalance = params.BeaconConfig().MaxEffectiveBalance - params.BeaconConfig().MinDepositAmount
+		copy(cp, []byte{0xFF, 0xFF, 0x00, 0x00, 0xFF ^ (1 << targetFlag), 0})
+		copy(pp, []byte{0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0xFF ^ (1 << targetFlag), 0x00, 0xFF, 0xFF})
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 1)
+		require.NoError(tt, err)
+		expectedActive -= params.BeaconConfig().MinDepositAmount
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, 2*params.BeaconConfig().MaxEffectiveBalance-params.BeaconConfig().MinDepositAmount, current)
+		require.Equal(tt, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+	})
+
+	t.Run("slash a validator", func(tt *testing.T) {
+		validators[1].Slashed = true
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 1)
+		require.NoError(tt, err)
+		expectedActive -= params.BeaconConfig().MaxEffectiveBalance
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, params.BeaconConfig().MaxEffectiveBalance-params.BeaconConfig().MinDepositAmount, current)
+		require.Equal(tt, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+	})
+	t.Run("Exit a validator", func(tt *testing.T) {
+		validators[4].ExitEpoch = 1
+		active, previous, current, err := UnrealizedCheckpointBalances(cp, pp, validators, 2)
+		require.NoError(tt, err)
+		expectedActive -= params.BeaconConfig().MaxEffectiveBalance
+		require.Equal(tt, expectedActive, active)
+		require.Equal(tt, params.BeaconConfig().MaxEffectiveBalance-params.BeaconConfig().MinDepositAmount, current)
+		require.Equal(tt, params.BeaconConfig().MaxEffectiveBalance, previous)
+	})
+}

beacon-chain/state/v1/getters_test.go

@@ -63,6 +63,8 @@ func TestNilState_NoPanic(t *testing.T) {
 	_ = st.PreviousJustifiedCheckpoint()
 	_ = st.CurrentJustifiedCheckpoint()
 	_ = st.FinalizedCheckpoint()
+	_, _, _, err = st.UnrealizedCheckpointBalances()
+	_ = err
 }
 
 func TestBeaconState_MatchCurrentJustifiedCheckpt(t *testing.T) {

beacon-chain/state/v1/unsupported_getters.go

@@ -15,6 +15,11 @@ func (*BeaconState) PreviousEpochParticipation() ([]byte, error) {
 	return nil, errors.New("PreviousEpochParticipation is not supported for phase 0 beacon state")
 }
 
+// UnrealizedCheckpointBalances is not supported for phase 0 beacon state.
+func (*BeaconState) UnrealizedCheckpointBalances() (uint64, uint64, uint64, error) {
+	return 0, 0, 0, errors.New("UnrealizedCheckpointBalances is not supported for phase0 beacon state")
+}
+
 // InactivityScores is not supported for phase 0 beacon state.
 func (*BeaconState) InactivityScores() ([]uint64, error) {
 	return nil, errors.New("InactivityScores is not supported for phase 0 beacon state")

beacon-chain/state/v2/BUILD.bazel

@@ -5,6 +5,7 @@ go_library(
     srcs = [
         "deprecated_getters.go",
         "deprecated_setters.go",
+        "error.go",
         "field_roots.go",
         "getters_block.go",
         "getters_checkpoint.go",
@@ -32,6 +33,7 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/beacon-chain/state/v2",
     visibility = ["//visibility:public"],
     deps = [
+        "//beacon-chain/core/time:go_default_library",
         "//beacon-chain/state:go_default_library",
         "//beacon-chain/state/fieldtrie:go_default_library",
         "//beacon-chain/state/state-native:go_default_library",
@@ -62,6 +64,7 @@ go_test(
         "deprecated_setters_test.go",
         "getters_block_test.go",
         "getters_checkpoint_test.go",
+        "getters_participation_test.go",
         "getters_test.go",
         "getters_validator_test.go",
         "proofs_test.go",

beacon-chain/state/v2/error.go

@@ -0,0 +1,5 @@
+package v2
+
+import "errors"
+
+var ErrNilParticipation = errors.New("Nil epoch participation in state")

beacon-chain/state/v2/getters_participation.go

@@ -1,5 +1,10 @@
 package v2
 
+import (
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/time"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stateutil"
+)
+
 // CurrentEpochParticipation corresponding to participation bits on the beacon chain.
 func (b *BeaconState) CurrentEpochParticipation() ([]byte, error) {
 	if !b.hasInnerState() {
@@ -30,6 +35,26 @@ func (b *BeaconState) PreviousEpochParticipation() ([]byte, error) {
 	return b.previousEpochParticipation(), nil
 }
 
+// UnrealizedCheckpointBalances returns the total balances: active, target attested in
+// current epoch and target attested in previous epoch. This function is used to
+// compute the "unrealized justification" that a synced Beacon Block will have.
+func (b *BeaconState) UnrealizedCheckpointBalances() (uint64, uint64, uint64, error) {
+	if !b.hasInnerState() {
+		return 0, 0, 0, ErrNilInnerState
+	}
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	cp := b.state.CurrentEpochParticipation
+	pp := b.state.PreviousEpochParticipation
+	if cp == nil || pp == nil {
+		return 0, 0, 0, ErrNilParticipation
+	}
+	currentEpoch := time.CurrentEpoch(b)
+	return stateutil.UnrealizedCheckpointBalances(cp, pp, b.state.Validators, currentEpoch)
+
+}
+
 // currentEpochParticipation corresponding to participation bits on the beacon chain.
 // This assumes that a lock is already held on BeaconState.
 func (b *BeaconState) currentEpochParticipation() []byte {

beacon-chain/state/v2/getters_participation_test.go

@@ -0,0 +1,64 @@
+package v2
+
+import (
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/config/params"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestState_UnrealizedCheckpointBalances(t *testing.T) {
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	balances := make([]uint64, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch:        params.BeaconConfig().FarFutureEpoch,
+			EffectiveBalance: params.BeaconConfig().MaxEffectiveBalance,
+		}
+		balances[i] = params.BeaconConfig().MaxEffectiveBalance
+	}
+	base := &ethpb.BeaconStateAltair{
+		Slot:        2,
+		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+
+		Validators:                 validators,
+		CurrentEpochParticipation:  make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		PreviousEpochParticipation: make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		Balances:                   balances,
+	}
+	state, err := InitializeFromProto(base)
+	require.NoError(t, err)
+
+	// No one voted in the last two epochs
+	allActive := params.BeaconConfig().MinGenesisActiveValidatorCount * params.BeaconConfig().MaxEffectiveBalance
+	active, previous, current, err := state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, uint64(0), previous)
+
+	// Add some votes in the last two epochs:
+	base.CurrentEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[1] = 0xFF
+
+	state, err = InitializeFromProto(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, current)
+	require.Equal(t, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+
+	// Slash some validators
+	validators[0].Slashed = true
+	state, err = InitializeFromProto(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive-params.BeaconConfig().MaxEffectiveBalance, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, previous)
+
+}

beacon-chain/state/v2/getters_test.go

@@ -74,6 +74,8 @@ func TestNilState_NoPanic(t *testing.T) {
 	require.ErrorIs(t, ErrNilInnerState, err)
 	_, err = st.NextSyncCommittee()
 	require.ErrorIs(t, ErrNilInnerState, err)
+	_, _, _, err = st.UnrealizedCheckpointBalances()
+	require.ErrorIs(t, ErrNilInnerState, err)
 }
 
 func TestBeaconState_MatchCurrentJustifiedCheckpt(t *testing.T) {

beacon-chain/state/v3/BUILD.bazel

@@ -5,6 +5,7 @@ go_library(
     srcs = [
         "deprecated_getters.go",
         "deprecated_setters.go",
+        "error.go",
         "field_roots.go",
         "getters_block.go",
         "getters_checkpoint.go",
@@ -34,6 +35,7 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/beacon-chain/state/v3",
     visibility = ["//visibility:public"],
     deps = [
+        "//beacon-chain/core/time:go_default_library",
         "//beacon-chain/state:go_default_library",
         "//beacon-chain/state/fieldtrie:go_default_library",
         "//beacon-chain/state/state-native:go_default_library",
@@ -64,6 +66,7 @@ go_test(
         "deprecated_setters_test.go",
         "getters_block_test.go",
         "getters_checkpoint_test.go",
+        "getters_participation_test.go",
         "getters_test.go",
         "getters_validator_test.go",
         "proofs_test.go",

beacon-chain/state/v3/error.go

@@ -0,0 +1,5 @@
+package v3
+
+import "errors"
+
+var ErrNilParticipation = errors.New("Nil epoch participation in state")

beacon-chain/state/v3/getters_participation.go

@@ -1,5 +1,10 @@
 package v3
 
+import (
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/time"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stateutil"
+)
+
 // CurrentEpochParticipation corresponding to participation bits on the beacon chain.
 func (b *BeaconState) CurrentEpochParticipation() ([]byte, error) {
 	if !b.hasInnerState() {
@@ -30,6 +35,26 @@ func (b *BeaconState) PreviousEpochParticipation() ([]byte, error) {
 	return b.previousEpochParticipation(), nil
 }
 
+// UnrealizedCheckpointBalances returns the total balances: active, target attested in
+// current epoch and target attested in previous epoch. This function is used to
+// compute the "unrealized justification" that a synced Beacon Block will have.
+func (b *BeaconState) UnrealizedCheckpointBalances() (uint64, uint64, uint64, error) {
+	if !b.hasInnerState() {
+		return 0, 0, 0, ErrNilInnerState
+	}
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	cp := b.state.CurrentEpochParticipation
+	pp := b.state.PreviousEpochParticipation
+	if cp == nil || pp == nil {
+		return 0, 0, 0, ErrNilParticipation
+	}
+	currentEpoch := time.CurrentEpoch(b)
+	return stateutil.UnrealizedCheckpointBalances(cp, pp, b.state.Validators, currentEpoch)
+
+}
+
 // currentEpochParticipation corresponding to participation bits on the beacon chain.
 // This assumes that a lock is already held on BeaconState.
 func (b *BeaconState) currentEpochParticipation() []byte {

beacon-chain/state/v3/getters_participation_test.go

@@ -0,0 +1,64 @@
+package v3
+
+import (
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/config/params"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestState_UnrealizedCheckpointBalances(t *testing.T) {
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	balances := make([]uint64, params.BeaconConfig().MinGenesisActiveValidatorCount)
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch:        params.BeaconConfig().FarFutureEpoch,
+			EffectiveBalance: params.BeaconConfig().MaxEffectiveBalance,
+		}
+		balances[i] = params.BeaconConfig().MaxEffectiveBalance
+	}
+	base := &ethpb.BeaconStateBellatrix{
+		Slot:        2,
+		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+
+		Validators:                 validators,
+		CurrentEpochParticipation:  make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		PreviousEpochParticipation: make([]byte, params.BeaconConfig().MinGenesisActiveValidatorCount),
+		Balances:                   balances,
+	}
+	state, err := InitializeFromProto(base)
+	require.NoError(t, err)
+
+	// No one voted in the last two epochs
+	allActive := params.BeaconConfig().MinGenesisActiveValidatorCount * params.BeaconConfig().MaxEffectiveBalance
+	active, previous, current, err := state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, uint64(0), previous)
+
+	// Add some votes in the last two epochs:
+	base.CurrentEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[0] = 0xFF
+	base.PreviousEpochParticipation[1] = 0xFF
+
+	state, err = InitializeFromProto(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive, active)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, current)
+	require.Equal(t, 2*params.BeaconConfig().MaxEffectiveBalance, previous)
+
+	// Slash some validators
+	validators[0].Slashed = true
+	state, err = InitializeFromProto(base)
+	require.NoError(t, err)
+	active, previous, current, err = state.UnrealizedCheckpointBalances()
+	require.NoError(t, err)
+	require.Equal(t, allActive-params.BeaconConfig().MaxEffectiveBalance, active)
+	require.Equal(t, uint64(0), current)
+	require.Equal(t, params.BeaconConfig().MaxEffectiveBalance, previous)
+
+}

beacon-chain/state/v3/getters_test.go

@@ -75,6 +75,8 @@ func TestNilState_NoPanic(t *testing.T) {
 	require.ErrorIs(t, ErrNilInnerState, err)
 	_, err = st.LatestExecutionPayloadHeader()
 	require.ErrorIs(t, ErrNilInnerState, err)
+	_, _, _, err = st.UnrealizedCheckpointBalances()
+	require.ErrorIs(t, ErrNilInnerState, err)
 
 }