Implement get_ptc

This implements a helper to get the ptc committee from a state. It uses
the cached beacon committees if possible

It also implements a helper to compute the largest power of two of a
uint64 and a helper to test for nil payload attestation messages

beacon-chain/core/helpers/BUILD.bazel

@@ -8,6 +8,7 @@ go_library(
         "block.go",
         "genesis.go",
         "metrics.go",
+        "payload_attestation.go",
         "randao.go",
         "rewards_penalties.go",
         "shuffle.go",
@@ -53,6 +54,8 @@ go_test(
         "attestation_test.go",
         "beacon_committee_test.go",
         "block_test.go",
+        "exports_test.go",
+        "payload_attestation_test.go",
         "private_access_fuzz_noop_test.go",  # keep
         "private_access_test.go",
         "randao_test.go",
@@ -84,6 +87,7 @@ go_test(
         "//testing/assert:go_default_library",
         "//testing/require:go_default_library",
         "//testing/util:go_default_library",
+        "//testing/util/random:go_default_library",
         "//time:go_default_library",
         "//time/slots:go_default_library",
         "@com_github_prysmaticlabs_go_bitfield//:go_default_library",

beacon-chain/core/helpers/exports_test.go

@@ -0,0 +1,12 @@
+package helpers
+
+var (
+	ErrNilMessage            = errNilMessage
+	ErrNilData               = errNilData
+	ErrNilBeaconBlockRoot    = errNilBeaconBlockRoot
+	ErrNilPayloadAttestation = errNilPayloadAttestation
+	ErrNilSignature          = errNilSignature
+	ErrNilAggregationBits    = errNilAggregationBits
+	ErrPreEPBSState          = errPreEPBSState
+	ErrCommitteeOverflow     = errCommitteeOverflow
+)

beacon-chain/core/helpers/payload_attestation.go

@@ -0,0 +1,91 @@
+package helpers
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v5/beacon-chain/state"
+	fieldparams "github.com/prysmaticlabs/prysm/v5/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/v5/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v5/math"
+	eth "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/v5/runtime/version"
+	"github.com/prysmaticlabs/prysm/v5/time/slots"
+)
+
+var (
+	errNilMessage            = errors.New("nil PayloadAttestationMessage")
+	errNilData               = errors.New("nil PayloadAttestationData")
+	errNilBeaconBlockRoot    = errors.New("nil BeaconBlockRoot")
+	errNilPayloadAttestation = errors.New("nil PayloadAttestation")
+	errNilSignature          = errors.New("nil Signature")
+	errNilAggregationBits    = errors.New("nil AggregationBits")
+	errPreEPBSState          = errors.New("beacon state pre ePBS fork")
+	errCommitteeOverflow     = errors.New("beacon committee of insufficient size")
+)
+
+// ValidateNilPayloadAttestationData checks if any composite field of the
+// payload attestation data is nil
+func ValidateNilPayloadAttestationData(data *eth.PayloadAttestationData) error {
+	if data == nil {
+		return errNilData
+	}
+	if data.BeaconBlockRoot == nil {
+		return errNilBeaconBlockRoot
+	}
+	return nil
+}
+
+// ValidateNilPayloadAttestationMessage checks if any composite field of the
+// payload attestation message is nil
+func ValidateNilPayloadAttestationMessage(att *eth.PayloadAttestationMessage) error {
+	if att == nil {
+		return errNilMessage
+	}
+	if att.Signature == nil {
+		return errNilSignature
+	}
+	return ValidateNilPayloadAttestationData(att.Data)
+}
+
+// ValidateNilPayloadAttestation checks if any composite field of the
+// payload attestation is nil
+func ValidateNilPayloadAttestation(att *eth.PayloadAttestation) error {
+	if att == nil {
+		return errNilPayloadAttestation
+	}
+	if att.AggregationBits == nil {
+		return errNilAggregationBits
+	}
+	if att.Signature == nil {
+		return errNilSignature
+	}
+	return ValidateNilPayloadAttestationData(att.Data)
+}
+
+// GetPayloadTimelinessCommittee returns the PTC for the given slot, computed from the passed state as in the
+// spec function `get_ptc`.
+func GetPayloadTimelinessCommittee(ctx context.Context, state state.ReadOnlyBeaconState, slot primitives.Slot) (indices []primitives.ValidatorIndex, err error) {
+	if state.Version() < version.EPBS {
+		return nil, errPreEPBSState
+	}
+	epoch := slots.ToEpoch(slot)
+	activeCount, err := ActiveValidatorCount(ctx, state, epoch)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not compute active validator count")
+	}
+	committeesPerSlot := math.LargestPowerOfTwo(math.Min(SlotCommitteeCount(activeCount), fieldparams.PTCSize))
+	membersPerCommittee := fieldparams.PTCSize / committeesPerSlot
+	for i := uint64(0); i <= committeesPerSlot; i++ {
+		committee, err := BeaconCommitteeFromState(ctx, state, slot, primitives.CommitteeIndex(i))
+		if err != nil {
+			return nil, err
+		}
+		if uint64(len(committee)) < membersPerCommittee {
+			return nil, errCommitteeOverflow
+		}
+		start := uint64(len(committee)) - membersPerCommittee
+		indices = append(indices, committee[start:]...)
+	}
+	return
+}

beacon-chain/core/helpers/payload_attestation_test.go

@@ -0,0 +1,92 @@
+package helpers_test
+
+import (
+	"context"
+	"strconv"
+	"testing"
+
+	"github.com/prysmaticlabs/go-bitfield"
+	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/helpers"
+	state_native "github.com/prysmaticlabs/prysm/v5/beacon-chain/state/state-native"
+	fieldparams "github.com/prysmaticlabs/prysm/v5/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/v5/config/params"
+	"github.com/prysmaticlabs/prysm/v5/math"
+	eth "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
+	ethpb "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/v5/testing/require"
+	"github.com/prysmaticlabs/prysm/v5/testing/util/random"
+	"github.com/prysmaticlabs/prysm/v5/time/slots"
+)
+
+func TestValidateNilPayloadAttestation(t *testing.T) {
+	require.ErrorIs(t, helpers.ErrNilData, helpers.ValidateNilPayloadAttestationData(nil))
+	data := &eth.PayloadAttestationData{}
+	require.ErrorIs(t, helpers.ErrNilBeaconBlockRoot, helpers.ValidateNilPayloadAttestationData(data))
+	data.BeaconBlockRoot = make([]byte, 32)
+	require.NoError(t, helpers.ValidateNilPayloadAttestationData(data))
+
+	require.ErrorIs(t, helpers.ErrNilMessage, helpers.ValidateNilPayloadAttestationMessage(nil))
+	message := &eth.PayloadAttestationMessage{}
+	require.ErrorIs(t, helpers.ErrNilSignature, helpers.ValidateNilPayloadAttestationMessage(message))
+	message.Signature = make([]byte, 96)
+	require.ErrorIs(t, helpers.ErrNilData, helpers.ValidateNilPayloadAttestationMessage(message))
+	message.Data = data
+	require.NoError(t, helpers.ValidateNilPayloadAttestationMessage(message))
+
+	require.ErrorIs(t, helpers.ErrNilPayloadAttestation, helpers.ValidateNilPayloadAttestation(nil))
+	att := &eth.PayloadAttestation{}
+	require.ErrorIs(t, helpers.ErrNilAggregationBits, helpers.ValidateNilPayloadAttestation(att))
+	att.AggregationBits = bitfield.NewBitvector512()
+	require.ErrorIs(t, helpers.ErrNilSignature, helpers.ValidateNilPayloadAttestation(att))
+	att.Signature = message.Signature
+	require.ErrorIs(t, helpers.ErrNilData, helpers.ValidateNilPayloadAttestation(att))
+	att.Data = data
+	require.NoError(t, helpers.ValidateNilPayloadAttestation(att))
+}
+
+func TestGetPayloadTimelinessCommittee(t *testing.T) {
+	helpers.ClearCache()
+
+	// Create 10 committees
+	committeeCount := uint64(10)
+	validatorCount := committeeCount * params.BeaconConfig().TargetCommitteeSize * uint64(params.BeaconConfig().SlotsPerEpoch)
+	validators := make([]*ethpb.Validator, validatorCount)
+
+	for i := 0; i < len(validators); i++ {
+		k := make([]byte, 48)
+		copy(k, strconv.Itoa(i))
+		validators[i] = &ethpb.Validator{
+			PublicKey:             k,
+			WithdrawalCredentials: make([]byte, 32),
+			ExitEpoch:             params.BeaconConfig().FarFutureEpoch,
+		}
+	}
+
+	state, err := state_native.InitializeFromProtoEpbs(random.BeaconState(t))
+	require.NoError(t, err)
+	require.NoError(t, state.SetValidators(validators))
+	require.NoError(t, state.SetSlot(200))
+
+	ctx := context.Background()
+	indices, err := helpers.BeaconCommitteeFromState(ctx, state, state.Slot(), 1)
+	require.NoError(t, err)
+	require.Equal(t, 128, len(indices))
+
+	epoch := slots.ToEpoch(state.Slot())
+	activeCount, err := helpers.ActiveValidatorCount(ctx, state, epoch)
+	require.NoError(t, err)
+	require.Equal(t, uint64(40960), activeCount)
+
+	computedCommitteeCount := helpers.SlotCommitteeCount(activeCount)
+	require.Equal(t, committeeCount, computedCommitteeCount)
+	committeesPerSlot := math.LargestPowerOfTwo(math.Min(committeeCount, fieldparams.PTCSize))
+	require.Equal(t, uint64(8), committeesPerSlot)
+
+	ptc, err := helpers.GetPayloadTimelinessCommittee(ctx, state, state.Slot())
+	require.NoError(t, err)
+
+	committee1, err := helpers.BeaconCommitteeFromState(ctx, state, state.Slot(), 0)
+	require.NoError(t, err)
+
+	require.DeepEqual(t, committee1[len(committee1)-64:], ptc[:64])
+}

math/math_helper.go

@@ -116,6 +116,21 @@ func PowerOf2(n uint64) uint64 {
 	return 1 << n
 }
 
+// LargestPowerOfTwo returns the largest power of 2 that is lower or equal than
+// the parameter
+func LargestPowerOfTwo(n uint64) uint64 {
+	if n == 0 {
+		return 0
+	}
+	n |= n >> 1
+	n |= n >> 2
+	n |= n >> 4
+	n |= n >> 8
+	n |= n >> 16
+	n |= n >> 32
+	return n - (n >> 1)
+}
+
 // Max returns the larger integer of the two
 // given ones.This is used over the Max function
 // in the standard math library because that max function

math/math_helper_test.go

@@ -549,3 +549,27 @@ func TestAddInt(t *testing.T) {
 		})
 	}
 }
+
+func TestLargestPowerOfTwo(t *testing.T) {
+	testCases := []struct {
+		name     string
+		input    uint64
+		expected uint64
+	}{
+		{"Zero", 0, 0},
+		{"One", 1, 1},
+		{"Just below power of two", 14, 8},
+		{"Power of two", 16, 16},
+		{"Large number", 123456789, 67108864},
+		{"Max uint64", 18446744073709551615, 9223372036854775808},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			result := math.LargestPowerOfTwo(tc.input)
+			if result != tc.expected {
+				t.Errorf("For input %d, expected %d but got %d", tc.input, tc.expected, result)
+			}
+		})
+	}
+}