More Efficient Validation of Proposer Index (#8107)

* metric

* make it better

* make it better

* gaz

Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>

beacon-chain/sync/metrics.go

@@ -47,6 +47,7 @@ var (
 			Help: "Count the number of times a node resyncs.",
 		},
 	)
+
 	arrivalBlockPropagationHistogram = promauto.NewHistogram(
 		prometheus.HistogramOpts{
 			Name:    "block_arrival_latency_milliseconds",

beacon-chain/sync/validate_beacon_blocks.go

@@ -136,7 +136,8 @@ func (s *Service) validateBeaconBlockPubSub(ctx context.Context, pid peer.ID, ms
 		log.WithError(err).WithField("blockSlot", blk.Block.Slot).Warn("Rejected block")
 		return pubsub.ValidationReject
 	}
-
+	// Record attribute of valid block.
+	span.AddAttributes(trace.Int64Attribute("slotInEpoch", int64(blk.Block.Slot%params.BeaconConfig().SlotsPerEpoch)))
 	msg.ValidatorData = blk // Used in downstream subscriber
 	return pubsub.ValidationAccept
 }
@@ -167,10 +168,26 @@ func (s *Service) validateBeaconBlock(ctx context.Context, blk *ethpb.SignedBeac
 		s.setBadBlock(ctx, blockRoot)
 		return err
 	}
-
-	parentState, err = state.ProcessSlots(ctx, parentState, blk.Block.Slot)
-	if err != nil {
-		return err
+	// There is an epoch lookahead for validator proposals
+	// for the next epoch from the start of our current epoch. We
+	// use the randao mix at the end of the previous epoch as the seed
+	// to determine proposals.
+	// Seed for Next Epoch => Derived From Randao Mix at the end of the Previous Epoch.
+	// Which is why we simply set the slot over here.
+	nextEpoch := helpers.NextEpoch(parentState)
+	expectedEpoch := helpers.SlotToEpoch(blk.Block.Slot)
+	if expectedEpoch <= nextEpoch {
+		err = parentState.SetSlot(blk.Block.Slot)
+		if err != nil {
+			return err
+		}
+	} else {
+		// In the event the block is more than an epoch ahead from its
+		// parent state, we have to advance the state forward.
+		parentState, err = state.ProcessSlots(ctx, parentState, blk.Block.Slot)
+		if err != nil {
+			return err
+		}
 	}
 	idx, err := helpers.BeaconProposerIndex(parentState)
 	if err != nil {

beacon-chain/sync/validate_beacon_blocks_test.go

@@ -244,6 +244,69 @@ func TestValidateBeaconBlockPubSub_ValidProposerSignature(t *testing.T) {
 	assert.NotNil(t, m.ValidatorData, "Decoded message was not set on the message validator data")
 }
 
+func TestValidateBeaconBlockPubSub_WithLookahead(t *testing.T) {
+	db, stateSummaryCache := dbtest.SetupDB(t)
+	p := p2ptest.NewTestP2P(t)
+	ctx := context.Background()
+	beaconState, privKeys := testutil.DeterministicGenesisState(t, 100)
+	parentBlock := testutil.NewBeaconBlock()
+	require.NoError(t, db.SaveBlock(ctx, parentBlock))
+	bRoot, err := parentBlock.Block.HashTreeRoot()
+	require.NoError(t, err)
+	require.NoError(t, db.SaveState(ctx, beaconState, bRoot))
+	require.NoError(t, db.SaveStateSummary(ctx, &pb.StateSummary{Root: bRoot[:]}))
+	copied := beaconState.Copy()
+	// The next block is only 1 epoch ahead so as to not induce a new seed.
+	blkSlot := params.BeaconConfig().SlotsPerEpoch * helpers.NextEpoch(copied)
+	copied, err = state.ProcessSlots(context.Background(), copied, blkSlot)
+	require.NoError(t, err)
+	proposerIdx, err := helpers.BeaconProposerIndex(copied)
+	require.NoError(t, err)
+	msg := testutil.NewBeaconBlock()
+	msg.Block.ProposerIndex = proposerIdx
+	msg.Block.Slot = blkSlot
+	msg.Block.ParentRoot = bRoot[:]
+	msg.Signature, err = helpers.ComputeDomainAndSign(beaconState, 0, msg.Block, params.BeaconConfig().DomainBeaconProposer, privKeys[proposerIdx])
+	require.NoError(t, err)
+
+	c, err := lru.New(10)
+	require.NoError(t, err)
+	c2, err := lru.New(10)
+	require.NoError(t, err)
+	stateGen := stategen.New(db, stateSummaryCache)
+	chainService := &mock.ChainService{Genesis: time.Unix(time.Now().Unix()-int64(blkSlot*params.BeaconConfig().SecondsPerSlot), 0),
+		State: beaconState,
+		FinalizedCheckPoint: &ethpb.Checkpoint{
+			Epoch: 0,
+		}}
+	r := &Service{
+		db:                  db,
+		p2p:                 p,
+		initialSync:         &mockSync.Sync{IsSyncing: false},
+		chain:               chainService,
+		blockNotifier:       chainService.BlockNotifier(),
+		seenBlockCache:      c,
+		badBlockCache:       c2,
+		slotToPendingBlocks: gcache.New(time.Second, 2*time.Second),
+		seenPendingBlocks:   make(map[[32]byte]bool),
+		stateSummaryCache:   stateSummaryCache,
+		stateGen:            stateGen,
+	}
+	buf := new(bytes.Buffer)
+	_, err = p.Encoding().EncodeGossip(buf, msg)
+	require.NoError(t, err)
+	topic := p2p.GossipTypeMapping[reflect.TypeOf(msg)]
+	m := &pubsub.Message{
+		Message: &pubsubpb.Message{
+			Data:  buf.Bytes(),
+			Topic: &topic,
+		},
+	}
+	result := r.validateBeaconBlockPubSub(ctx, "", m) == pubsub.ValidationAccept
+	assert.Equal(t, true, result)
+	assert.NotNil(t, m.ValidatorData, "Decoded message was not set on the message validator data")
+}
+
 func TestValidateBeaconBlockPubSub_AdvanceEpochsForState(t *testing.T) {
 	db, stateSummaryCache := dbtest.SetupDB(t)
 	p := p2ptest.NewTestP2P(t)