Unrealized justification

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

@@ -2,13 +2,32 @@ 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"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"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,
-	totalActiveBalance, prevEpochTargetBalance, currEpochTargetBalance uint64) (state.BeaconState, error) {
+func computeCheckpoints(state state.BeaconState, newBits bitfield.Bitvector4) (*ethpb.Checkpoint, *ethpb.Checkpoint, error) {
 	prevEpoch := time.PrevEpoch(state)
 	currentEpoch := time.CurrentEpoch(state)
 	oldPrevJustifiedCheckpoint := state.PreviousJustifiedCheckpoint()
 	oldCurrJustifiedCheckpoint := state.CurrentJustifiedCheckpoint()
 
-	// Process justifications
-	if err := state.SetPreviousJustifiedCheckpoint(state.CurrentJustifiedCheckpoint()); err != nil {
-		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
-		}
-	}
+	justifiedCheckpoint := state.CurrentJustifiedCheckpoint()
+	finalizedCheckpoint := state.FinalizedCheckpoint()
 
 	// 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 {
-			return nil, err
-		}
-		newBits = state.JustificationBits()
-		newBits.SetBitAt(0, true)
-		if err := state.SetJustificationBits(newBits); err != nil {
-			return nil, err
+		justifiedCheckpoint.Epoch = currentEpoch
+		justifiedCheckpoint.Root = blockRoot
+	} else if newBits.BitAt(1) {
+		// If 2/3 or more of total balance attested in the previous epoch.
+		blockRoot, err := helpers.BlockRoot(state, prevEpoch)
+		if err != nil {
+			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 {
-			return nil, err
-		}
+		finalizedCheckpoint = oldPrevJustifiedCheckpoint
 	}
 
 	// 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 {
-			return nil, err
-		}
+		finalizedCheckpoint = oldPrevJustifiedCheckpoint
 	}
 
 	// 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 {
-			return nil, err
-		}
+		finalizedCheckpoint = oldCurrJustifiedCheckpoint
 	}
 
 	// 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 {
-			return nil, err
-		}
+		finalizedCheckpoint = oldCurrJustifiedCheckpoint
 	}
-
-	return state, nil
+	return justifiedCheckpoint, finalizedCheckpoint, 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)