Fix

consensus/polybft/mocks_test.go

@@ -395,6 +395,12 @@ func (tp *syncerMock) Sync(func(*types.FullBlock) bool) error {
 	return args.Error(0)
 }
 
+func (tp *syncerMock) IsSyncingWithPeer() bool {
+	args := tp.Called()
+
+	return args.Bool(0)
+}
+
 func init() {
 	// setup custom hash header func
 	setupHeaderHashFunc()

consensus/polybft/polybft.go

@@ -599,12 +599,24 @@ func (p *Polybft) startConsensusProtocol() {
 				if ev.Source == "syncer" && ev.NewChain[0].Number >= p.blockchain.CurrentHeader().Number {
 					p.logger.Info("sync block notification received", "block height", ev.NewChain[0].Number,
 						"current height", p.blockchain.CurrentHeader().Number)
-					syncerBlockCh <- struct{}{}
+
+					select {
+					case syncerBlockCh <- struct{}{}:
+					default:
+					}
 				}
 			}
 		}
 	}()
 
+	// wait until he stops syncing
+	p.logger.Info("waiting to stop syncing so that we can try to join consensus if node is a validator")
+
+	for p.syncer.IsSyncingWithPeer() {
+	}
+
+	p.logger.Info("node synced up on start. Trying to join consensus if validator")
+
 	var (
 		sequenceCh   <-chan struct{}
 		stopSequence func()

e2e-polybft/e2e/consensus_test.go

@@ -1,6 +1,7 @@
 package e2e
 
 import (
+	"bytes"
 	"fmt"
 	"math/big"
 	"path"
@@ -53,22 +54,40 @@ func TestE2E_Consensus_Basic_WithNonValidators(t *testing.T) {
 	})
 
 	t.Run("sync protocol, drop single validator node", func(t *testing.T) {
+		validatorSrv := cluster.Servers[0]
+		validatorAcc, err := sidechain.GetAccountFromDir(validatorSrv.DataDir())
+		require.NoError(t, err)
+
 		// query the current block number, as it is a starting point for the test
-		currentBlockNum, err := cluster.Servers[0].JSONRPC().Eth().BlockNumber()
+		currentBlockNum, err := validatorSrv.JSONRPC().Eth().BlockNumber()
 		require.NoError(t, err)
 
+		// wait for 2 epochs to elapse, before we stop the node
+		require.NoError(t, cluster.WaitForBlock(currentBlockNum+2*epochSize, 2*time.Minute))
+
 		// stop one node
-		node := cluster.Servers[0]
-		node.Stop()
+		validatorSrv.Stop()
+
+		// check what is the current block on the running nodes
+		currentBlockNum, err = cluster.Servers[1].JSONRPC().Eth().BlockNumber()
+		require.NoError(t, err)
 
 		// wait for 2 epochs to elapse, so that rest of the network progresses
 		require.NoError(t, cluster.WaitForBlock(currentBlockNum+2*epochSize, 2*time.Minute))
 
 		// start the node again
-		node.Start()
+		validatorSrv.Start()
 
 		// wait 2 more epochs to elapse and make sure that stopped node managed to catch up
 		require.NoError(t, cluster.WaitForBlock(currentBlockNum+4*epochSize, 2*time.Minute))
+
+		// wait until the validator mines one block to check if he is back in consensus
+		require.NoError(t, cluster.WaitUntil(3*time.Minute, 2*time.Second, func() bool {
+			latestBlock, err := cluster.Servers[0].JSONRPC().Eth().GetBlockByNumber(ethgo.Latest, false)
+			require.NoError(t, err)
+
+			return bytes.Equal(validatorAcc.Address().Bytes(), latestBlock.Miner.Bytes())
+		}))
 	})
 
 	t.Run("sync protocol, drop single non-validator node", func(t *testing.T) {
@@ -87,7 +106,12 @@ func TestE2E_Consensus_Basic_WithNonValidators(t *testing.T) {
 		node.Start()
 
 		// wait 2 more epochs to elapse and make sure that stopped node managed to catch up
-		require.NoError(t, cluster.WaitForBlock(currentBlockNum+4*epochSize, 2*time.Minute))
+		blockToWait := currentBlockNum + 4*epochSize
+		require.NoError(t, cluster.WaitForBlock(blockToWait, 2*time.Minute))
+
+		latestBlockOnDroppedNode, err := node.JSONRPC().Eth().GetBlockByNumber(ethgo.Latest, false)
+		require.NoError(t, err)
+		require.GreaterOrEqual(t, latestBlockOnDroppedNode.Number, blockToWait)
 	})
 }
 

syncer/syncer.go

@@ -3,6 +3,7 @@ package syncer
 import (
 	"errors"
 	"fmt"
+	"sync/atomic"
 	"time"
 
 	"github.com/0xPolygon/polygon-edge/helper/progress"
@@ -38,6 +39,8 @@ type syncer struct {
 
 	// Channel to notify Sync that a new status arrived
 	newStatusCh chan struct{}
+
+	isSyncing atomic.Bool
 }
 
 func NewSyncer(
@@ -219,6 +222,9 @@ func (s *syncer) bulkSyncWithPeer(peerID peer.ID, peerLatestBlock uint64,
 		return 0, false, err
 	}
 
+	s.setIsSyncing(true)
+	defer s.setIsSyncing(false)
+
 	// Create a blockchain subscription for the sync progression and start tracking
 	subscription := s.blockchain.SubscribeEvents()
 	s.syncProgression.StartProgression(localLatest+1, subscription)
@@ -272,6 +278,16 @@ func (s *syncer) bulkSyncWithPeer(peerID peer.ID, peerLatestBlock uint64,
 	}
 }
 
+// setIsSyncing updates the isSyncing field
+func (s *syncer) setIsSyncing(isSyncing bool) {
+	s.isSyncing.Store(isSyncing)
+}
+
+// IsSyncingWithPeer indicates if node is syncing with peer
+func (s *syncer) IsSyncingWithPeer() bool {
+	return s.isSyncing.Load()
+}
+
 func updateMetrics(fullBlock *types.FullBlock) {
 	metrics.SetGauge([]string{syncerMetrics, "tx_num"}, float32(len(fullBlock.Block.Transactions)))
 	metrics.SetGauge([]string{syncerMetrics, "receipts_num"}, float32(len(fullBlock.Receipts)))

syncer/types.go

@@ -70,6 +70,8 @@ type Syncer interface {
 	HasSyncPeer() bool
 	// Sync starts routine to sync blocks
 	Sync(func(*types.FullBlock) bool) error
+
+	IsSyncingWithPeer() bool
 }
 
 type Progression interface {