Add PTC assignment support for Duty endpoint (#14032)

beacon-chain/core/helpers/beacon_committee.go

@@ -213,6 +213,7 @@ type CommitteeAssignment struct {
 	Committee      []primitives.ValidatorIndex
 	AttesterSlot   primitives.Slot
 	CommitteeIndex primitives.CommitteeIndex
+	PtcSlot        primitives.Slot
 }
 
 // verifyAssignmentEpoch verifies if the given epoch is valid for assignment based on the provided state.
@@ -303,6 +304,13 @@ func CommitteeAssignments(ctx context.Context, state state.BeaconState, epoch pr
 		vals[v] = struct{}{}
 	}
 	assignments := make(map[primitives.ValidatorIndex]*CommitteeAssignment)
+
+	activeValidatorCount, err := ActiveValidatorCount(ctx, state, epoch)
+	if err != nil {
+		return nil, err
+	}
+	ptcPerSlot, PtcMembersPerCommittee := PtcAllocation(activeValidatorCount)
+
 	// Compute committee assignments for each slot in the epoch.
 	for slot := startSlot; slot < startSlot+params.BeaconConfig().SlotsPerEpoch; slot++ {
 		committees, err := BeaconCommittees(ctx, state, slot)
@@ -321,11 +329,52 @@ func CommitteeAssignments(ctx context.Context, state state.BeaconState, epoch pr
 				assignments[vIndex].AttesterSlot = slot
 				assignments[vIndex].CommitteeIndex = primitives.CommitteeIndex(j)
 			}
+
+			// We only need to assign PTC slots for the first `PTCPerSlot` committees of a given slot.
+			if uint64(j) < ptcPerSlot {
+				assignments = PTCAssignments(committee, assignments, PtcMembersPerCommittee, slot)
+			}
 		}
 	}
 	return assignments, nil
 }
 
+// PTCAssignments updates the PTC slot assignments for the given committee members.
+// committee: a slice of ValidatorIndex representing committee members.
+// assignments: a map of ValidatorIndex to CommitteeAssignment where assignments will be updated.
+// membersPerCommittee: the number of members to be assigned to the PTC committee.
+// slot: the slot to be assigned for PTC assignment.
+// Returns the updated assignments map.
+func PTCAssignments(committee []primitives.ValidatorIndex,
+	assignments map[primitives.ValidatorIndex]*CommitteeAssignment,
+	membersPerCommittee uint64,
+	slot primitives.Slot) map[primitives.ValidatorIndex]*CommitteeAssignment {
+	committeeLength := uint64(len(committee))
+	// If the number of PTC members is greater than Beacon members,
+	// return the current assignments without changes.
+	if membersPerCommittee > committeeLength {
+		return assignments
+	}
+
+	// Calculate the starting index for PTC committee.
+	ptcStartIndex := committeeLength - membersPerCommittee
+
+	// Loop through the selected committee members for PTC assignments.
+	for i := ptcStartIndex; i < committeeLength; i++ {
+		vIndex := committee[i]
+
+		assignment, exists := assignments[vIndex]
+		if !exists {
+			assignment = &CommitteeAssignment{}
+			assignments[vIndex] = assignment
+		}
+
+		assignment.PtcSlot = slot
+	}
+
+	return assignments
+}
+
 // VerifyBitfieldLength verifies that a bitfield length matches the given committee size.
 func VerifyBitfieldLength(bf bitfield.Bitfield, committeeSize uint64) error {
 	if bf.Len() != committeeSize {

beacon-chain/core/helpers/beacon_committee_test.go

@@ -3,6 +3,7 @@ package helpers_test
 import (
 	"context"
 	"fmt"
+	"slices"
 	"strconv"
 	"testing"
 
@@ -10,6 +11,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/time"
 	state_native "github.com/prysmaticlabs/prysm/v5/beacon-chain/state/state-native"
+	field_params "github.com/prysmaticlabs/prysm/v5/config/fieldparams"
 	"github.com/prysmaticlabs/prysm/v5/config/params"
 	"github.com/prysmaticlabs/prysm/v5/consensus-types/primitives"
 	"github.com/prysmaticlabs/prysm/v5/container/slice"
@@ -717,15 +719,26 @@ func TestCommitteeIndices(t *testing.T) {
 	assert.DeepEqual(t, []primitives.CommitteeIndex{0, 1, 3}, indices)
 }
 
-func TestAttestationCommittees(t *testing.T) {
-	validators := make([]*ethpb.Validator, params.BeaconConfig().SlotsPerEpoch.Mul(params.BeaconConfig().TargetCommitteeSize))
+func TestCommitteeAssignments_PTC(t *testing.T) {
+	helpers.ClearCache()
+	// Create 10 committees. Total 40960 validators.
+	committeeCount := uint64(10)
+	validatorCount := committeeCount * params.BeaconConfig().TargetCommitteeSize * uint64(params.BeaconConfig().SlotsPerEpoch)
+	validators := make([]*ethpb.Validator, validatorCount)
+	validatorIndices := make([]primitives.ValidatorIndex, validatorCount)
+
 	for i := 0; i < len(validators); i++ {
+		k := make([]byte, 48)
+		copy(k, strconv.Itoa(i))
 		validators[i] = &ethpb.Validator{
-			ExitEpoch: params.BeaconConfig().FarFutureEpoch,
+			PublicKey:             k,
+			WithdrawalCredentials: make([]byte, 32),
+			ExitEpoch:             params.BeaconConfig().FarFutureEpoch,
 		}
+		validatorIndices[i] = primitives.ValidatorIndex(i)
 	}
 
-	state, err := state_native.InitializeFromProtoPhase0(&ethpb.BeaconState{
+	state, err := state_native.InitializeFromProtoEpbs(&ethpb.BeaconStateEPBS{
 		Validators:  validators,
 		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
 	})
@@ -749,6 +762,31 @@ func TestAttestationCommittees(t *testing.T) {
 		assert.Equal(t, params.BeaconConfig().TargetCommitteeSize, uint64(len(committees[0])))
 		assert.Equal(t, params.BeaconConfig().TargetCommitteeSize, uint64(len(committees[1])))
 	})
+	as, err := helpers.CommitteeAssignments(context.Background(), state, 1, validatorIndices)
+	require.NoError(t, err)
+
+	// Capture all the slots and all the validator index that belonged in a PTC using a map for verification later.
+	slotValidatorMap := make(map[primitives.Slot][]primitives.ValidatorIndex)
+	for i, a := range as {
+		slotValidatorMap[a.PtcSlot] = append(slotValidatorMap[a.PtcSlot], i)
+	}
+
+	// Verify that all the slots have the correct number of PTC.
+	for s, v := range slotValidatorMap {
+		if s == 0 {
+			continue
+		}
+		// Make sure all the PTC are the correct size from the map.
+		require.Equal(t, len(v), field_params.PTCSize)
+
+		// Get the actual PTC from the beacon state using the helper function
+		ptc, err := helpers.GetPayloadTimelinessCommittee(context.Background(), state, s)
+		require.NoError(t, err)
+		for _, index := range ptc {
+			i := slices.Index(v, index)
+			require.NotEqual(t, -1, i) // PTC not found from the assignment map
+		}
+	}
 }
 
 func TestBeaconCommittees(t *testing.T) {

beacon-chain/core/helpers/payload_attestation.go

@@ -74,8 +74,7 @@ func GetPayloadTimelinessCommittee(ctx context.Context, state state.ReadOnlyBeac
 	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
+	committeesPerSlot, membersPerCommittee := PtcAllocation(activeCount)
 	for i := uint64(0); i < committeesPerSlot; i++ {
 		committee, err := BeaconCommitteeFromState(ctx, state, slot, primitives.CommitteeIndex(i))
 		if err != nil {
@@ -89,3 +88,13 @@ func GetPayloadTimelinessCommittee(ctx context.Context, state state.ReadOnlyBeac
 	}
 	return
 }
+
+// PtcAllocation returns:
+// 1. The number of beacon committees that PTC will borrow from in a slot.
+// 2. The number of validators that PTC will borrow from in a beacon committee.
+func PtcAllocation(totalActive uint64) (committeesPerSlot, membersPerCommittee uint64) {
+	slotCommittees := SlotCommitteeCount(totalActive)
+	committeesPerSlot = math.LargestPowerOfTwo(math.Min(slotCommittees, fieldparams.PTCSize))
+	membersPerCommittee = fieldparams.PTCSize / committeesPerSlot
+	return
+}

beacon-chain/core/helpers/payload_attestation_test.go

@@ -91,3 +91,27 @@ func TestGetPayloadTimelinessCommittee(t *testing.T) {
 
 	require.DeepEqual(t, committee1[len(committee1)-64:], ptc[:64])
 }
+
+func Test_PtcAllocation(t *testing.T) {
+	tests := []struct {
+		totalActive        uint64
+		memberPerCommittee uint64
+		committeesPerSlot  uint64
+	}{
+		{64, 512, 1},
+		{params.BeaconConfig().MinGenesisActiveValidatorCount, 128, 4},
+		{25600, 128, 4},
+		{256000, 16, 32},
+		{1024000, 8, 64},
+	}
+
+	for _, test := range tests {
+		committeesPerSlot, memberPerCommittee := helpers.PtcAllocation(test.totalActive)
+		if memberPerCommittee != test.memberPerCommittee {
+			t.Errorf("memberPerCommittee(%d) = %d; expected %d", test.totalActive, memberPerCommittee, test.memberPerCommittee)
+		}
+		if committeesPerSlot != test.committeesPerSlot {
+			t.Errorf("committeesPerSlot(%d) = %d; expected %d", test.totalActive, committeesPerSlot, test.committeesPerSlot)
+		}
+	}
+}

beacon-chain/rpc/prysm/v1alpha1/validator/duties.go

@@ -108,6 +108,7 @@ func (vs *Server) duties(ctx context.Context, req *ethpb.DutiesRequest) (*ethpb.
 				assignment.Committee = ca.Committee
 				assignment.AttesterSlot = ca.AttesterSlot
 				assignment.CommitteeIndex = ca.CommitteeIndex
+				assignment.PtcSlot = ca.PtcSlot
 			}
 			// Save the next epoch assignments.
 			ca, ok = nextEpochAssignments[idx]
@@ -115,6 +116,7 @@ func (vs *Server) duties(ctx context.Context, req *ethpb.DutiesRequest) (*ethpb.
 				nextAssignment.Committee = ca.Committee
 				nextAssignment.AttesterSlot = ca.AttesterSlot
 				nextAssignment.CommitteeIndex = ca.CommitteeIndex
+				nextAssignment.PtcSlot = ca.PtcSlot
 			}
 		} else {
 			// If the validator isn't in the beacon state, try finding their deposit to determine their status.

proto/prysm/v1alpha1/validator.proto

@@ -572,6 +572,9 @@ message DutiesResponse {
 
         // The number of committees in the duty's slot.
         uint64 committees_at_slot = 9;
+
+        // Slot at which a validator attest to payload attestation timeliness.
+        uint64 ptc_slot = 10 [(ethereum.eth.ext.cast_type) = "github.com/prysmaticlabs/prysm/v5/consensus-types/primitives.Slot"];
     }
 }