prysm-pulse/validator/client/validator_attest.go

package client

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/prysmaticlabs/go-bitfield"
	"github.com/prysmaticlabs/go-ssz"
	pbp2p "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/rpc/v1"
	ethpb "github.com/prysmaticlabs/prysm/proto/eth/v1alpha1"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/params"
	"github.com/prysmaticlabs/prysm/shared/roughtime"
	"github.com/prysmaticlabs/prysm/shared/slotutil"
	"go.opencensus.io/trace"
)

// SubmitAttestation completes the validator client's attester responsibility at a given slot.
// It fetches the latest beacon block head along with the latest canonical beacon state
// information in order to sign the block and include information about the validator's
// participation in voting on the block.
func (v *validator) SubmitAttestation(ctx context.Context, slot uint64, pubKey [48]byte) {
	ctx, span := trace.StartSpan(ctx, "validator.SubmitAttestation")
	defer span.End()

	span.AddAttributes(trace.StringAttribute("validator", fmt.Sprintf("%#x", pubKey)))
	log := log.WithField("pubKey", fmt.Sprintf("%#x", bytesutil.Trunc(pubKey[:])))

	assignment, err := v.assignment(pubKey)
	if err != nil {
		log.Errorf("Could not fetch validator assignment: %v", err)
		return
	}

	indexInCommittee, err := v.indexInCommittee(ctx, pubKey, assignment)
	if err != nil {
		log.Errorf("Could not get validator index in assignment: %v", err)
		return
	}

	v.waitToSlotMidpoint(ctx, slot)

	req := &pb.AttestationRequest{
		Slot:           slot,
		CommitteeIndex: assignment.CommitteeIndex,
	}
	data, err := v.attesterClient.RequestAttestation(ctx, req)
	if err != nil {
		log.Errorf("Could not request attestation to sign at slot %d: %v", slot, err)
		return
	}
	log = log.WithField("slot", data.Slot)
	log = log.WithField("committeeIndex", data.Index)

	sig, err := v.signAtt(ctx, pubKey, data)
	if err != nil {
		log.Errorf("Could not sign attestation: %v", err)
		return
	}

	custodyBitfield := bitfield.NewBitlist(uint64(len(assignment.Committee)))
	aggregationBitfield := bitfield.NewBitlist(uint64(len(assignment.Committee)))
	aggregationBitfield.SetBitAt(indexInCommittee, true)
	attestation := &ethpb.Attestation{
		Data:            data,
		CustodyBits:     custodyBitfield,
		AggregationBits: aggregationBitfield,
		Signature:       sig,
	}

	attResp, err := v.attesterClient.SubmitAttestation(ctx, attestation)
	if err != nil {
		log.Errorf("Could not submit attestation to beacon node: %v", err)
		return
	}

	headRoot := fmt.Sprintf("%#x", bytesutil.Trunc(data.BeaconBlockRoot))
	log.WithField("headRoot", headRoot).Info("Submitted new attestation")

	span.AddAttributes(
		trace.Int64Attribute("slot", int64(slot)),
		trace.StringAttribute("attestationHash", fmt.Sprintf("%#x", attResp.Root)),
		trace.Int64Attribute("committeeIndex", int64(data.Index)),
		trace.StringAttribute("blockRoot", fmt.Sprintf("%#x", data.BeaconBlockRoot)),
		trace.Int64Attribute("justifiedEpoch", int64(data.Source.Epoch)),
		trace.Int64Attribute("targetEpoch", int64(data.Target.Epoch)),
		trace.StringAttribute("bitfield", fmt.Sprintf("%#x", aggregationBitfield)),
	)
}

// waitToSlotMidpoint waits until halfway through the current slot period
// such that any blocks from this slot have time to reach the beacon node
// before creating the attestation.
func (v *validator) waitToSlotMidpoint(ctx context.Context, slot uint64) {
	_, span := trace.StartSpan(ctx, "validator.waitToSlotMidpoint")
	defer span.End()

	half := params.BeaconConfig().SecondsPerSlot / 2
	delay := time.Duration(half) * time.Second
	if half == 0 {
		delay = 500 * time.Millisecond
	}
	startTime := slotutil.SlotStartTime(v.genesisTime, slot)
	timeToBroadcast := startTime.Add(delay)
	time.Sleep(roughtime.Until(timeToBroadcast))
}

// Given the validator public key, this gets the validator assignment.
func (v *validator) assignment(pubKey [48]byte) (*pb.AssignmentResponse_ValidatorAssignment, error) {
	if v.assignments == nil {
		return nil, errors.New("no assignments for validators")
	}

	for _, assign := range v.assignments.ValidatorAssignment {
		if bytes.Equal(pubKey[:], assign.PublicKey) {
			return assign, nil
		}
	}

	return nil, fmt.Errorf("pubkey %#x not in assignment", bytesutil.Trunc(pubKey[:]))
}

// This returns the index of validator's position in a committee. It's used to construct aggregation and
// custody bit fields.
func (v *validator) indexInCommittee(
	ctx context.Context,
	pubKey [48]byte,
	assignment *pb.AssignmentResponse_ValidatorAssignment) (uint64, error) {
	res, err := v.validatorClient.ValidatorIndex(ctx, &pb.ValidatorIndexRequest{PublicKey: pubKey[:]})
	if err != nil {
		return 0, err
	}

	for i, validatorIndex := range assignment.Committee {
		if validatorIndex == res.Index {
			return uint64(i), nil
		}
	}

	return 0, fmt.Errorf("index %d not in committee", res.Index)
}

// Given validator's public key, this returns the signature of an attestation data.
func (v *validator) signAtt(ctx context.Context, pubKey [48]byte, data *ethpb.AttestationData) ([]byte, error) {
	domain, err := v.validatorClient.DomainData(ctx, &pb.DomainRequest{Epoch: data.Target.Epoch, Domain: params.BeaconConfig().DomainBeaconAttester})
	if err != nil {
		return nil, err
	}
	attDataAndCustodyBit := &pbp2p.AttestationDataAndCustodyBit{
		Data: data,
		// Default is false until phase 1 where proof of custody gets implemented.
		CustodyBit: false,
	}

	root, err := ssz.HashTreeRoot(attDataAndCustodyBit)
	if err != nil {
		return nil, err
	}

	sig := v.keys[pubKey].SecretKey.Sign(root[:], domain.SignatureDomain)
	return sig.Marshal(), nil
}