feat: Add logic to append validator position in attestation

pkg/clmimicry/gossipsub_single_attestation.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/attestantio/go-eth2-client/spec/phase0"
 	v1 "github.com/ethpandaops/xatu/pkg/proto/eth/v1"
 	"github.com/ethpandaops/xatu/pkg/proto/libp2p"
 	"github.com/ethpandaops/xatu/pkg/proto/xatu"
@@ -138,5 +139,21 @@ func (m *Mimicry) createAdditionalGossipSubSingleAttestationData(
 	extra.MessageId = wrapperspb.String(payload.MsgID)
 	extra.MessageSize = wrapperspb.UInt32(uint32(payload.MsgSize))
 
+	// If the attestation is not aggregated, we can append the validator position within the committee.
+	if payload.SingleAttestation.GetAggregationBits().Count() == 1 {
+		validatorIndex, err := m.ethereum.Duties().GetValidatorIndex(
+			phase0.Epoch(epoch.Number()),
+			phase0.Slot(attestationData.GetSlot()),
+			phase0.CommitteeIndex(attestationData.GetCommitteeIndex()),
+			uint64(payload.SingleAttestation.GetAggregationBits().BitIndices()[0]),
+		)
+		if err == nil {
+			extra.AttestingValidator = &xatu.AttestingValidatorV2{
+				CommitteeIndex: &wrapperspb.UInt64Value{Value: uint64(attestationData.GetCommitteeIndex())},
+				Index:          &wrapperspb.UInt64Value{Value: uint64(validatorIndex)},
+			}
+		}
+	}
+
 	return extra, nil
 }