Poll headers when WS is not available.

Author: davidcauchi

lib/blockchain/blockchain.go

@@ -118,6 +118,8 @@ type EVMClient interface {
 	RawJsonRPCCall(ctx context.Context, result interface{}, method string, params ...interface{}) error
 
 	GetEthClient() *ethclient.Client
+
+	InitializeHeaderSubscription() error
 }
 
 // NodeHeader header with the ID of the node that received it

lib/blockchain/ethereum.go

@@ -105,12 +105,9 @@ func newEVMClient(networkSettings EVMNetwork, logger zerolog.Logger) (EVMClient,
 		return nil, err
 	}
 	ec.gasStats = NewGasStats(ec.ID)
-	// Check if subscriptions are supported since HTTP does not support subscriptions.
-	if ec.Client.Client().SupportsSubscriptions() {
-		err = ec.subscribeToNewHeaders()
-		if err != nil {
-			return nil, err
-		}
+	// Initialize header subscription or polling
+	if err := ec.InitializeHeaderSubscription(); err != nil {
+		return nil, err
 	}
 	// Check if the chain supports EIP-1559
 	// https://eips.ethereum.org/EIPS/eip-1559
@@ -701,6 +698,40 @@ func (e *EthereumClient) WaitForFinalizedTx(txHash common.Hash) (*big.Int, time.
 	key := "txFinalizer-" + txHash.String()
 	e.AddHeaderEventSubscription(key, finalizer)
 	defer e.DeleteHeaderEventSubscription(key)
+
+	if !e.Client.Client().SupportsSubscriptions() {
+		go func() {
+			ticker := time.NewTicker(10 * time.Second)
+			defer ticker.Stop()
+
+			for {
+				select {
+				case <-finalizer.context.Done():
+					return
+				case <-ticker.C:
+					latestHeader, err := e.GetLatestFinalizedBlockHeader(context.Background())
+					if err != nil {
+						e.l.Err(err).Msg("Error fetching latest finalized header via HTTP polling")
+					}
+
+					nodeHeader := NodeHeader{
+						// NodeID: 0, // Assign appropriate NodeID if needed
+						SafeEVMHeader: SafeEVMHeader{
+							Hash:      latestHeader.Hash(),
+							Number:    latestHeader.Number,
+							Timestamp: time.Unix(int64(latestHeader.Time), 0),
+							BaseFee:   latestHeader.BaseFee,
+						},
+					}
+
+					err = finalizer.ReceiveHeader(nodeHeader)
+					if err != nil {
+						e.l.Err(err).Msg("Finalizer received error during HTTP polling")
+					}
+				}
+			}
+		}()
+	}
 	err = finalizer.Wait()
 	if err != nil {
 		return nil, time.Time{}, fmt.Errorf("error waiting for finalization: %w in network %s tx %s", err, e.GetNetworkName(), txHash.Hex())
@@ -1220,6 +1251,47 @@ func (e *EthereumClient) AvgBlockTime(ctx context.Context) (time.Duration, error
 	return averageBlockTime, nil
 }
 
+// InitializeHeaderSubscription initializes either subscription-based or polling-based header processing
+func (e *EthereumClient) InitializeHeaderSubscription() error {
+	if e.Client.Client().SupportsSubscriptions() {
+		return e.subscribeToNewHeaders()
+	}
+	// Fallback to polling if subscriptions are not supported
+	e.l.Info().Str("Network", e.NetworkConfig.Name).Msg("Subscriptions not supported. Using polling for new headers.")
+	return e.startPollingHeaders()
+}
+
+// startPollingHeaders starts a polling loop to fetch new headers at regular intervals
+func (e *EthereumClient) startPollingHeaders() error {
+	pollInterval := time.Second * 5
+	ticker := time.NewTicker(pollInterval)
+	e.subscriptionWg.Add(1)
+	go func() {
+		defer e.subscriptionWg.Done()
+		lastHeaderNumber := uint64(0)
+		for {
+			select {
+			case <-ticker.C:
+				latestHeader, err := e.HeaderByNumber(context.Background(), nil) // nil gets the latest header
+				if err != nil {
+					e.l.Error().Err(err).Msg("Error fetching latest header during polling")
+					continue
+				}
+				if latestHeader.Number.Uint64() > lastHeaderNumber {
+					lastHeaderNumber = latestHeader.Number.Uint64()
+					e.receiveHeader(latestHeader)
+				}
+			case <-e.doneChan:
+				e.l.Debug().Str("Network", e.NetworkConfig.Name).Msg("Polling loop cancelled")
+				ticker.Stop()
+				e.Client.Close()
+				return
+			}
+		}
+	}()
+	return nil
+}
+
 // EthereumMultinodeClient wraps the client and the BlockChain network to interact with an EVM based Blockchain with multiple nodes
 type EthereumMultinodeClient struct {
 	DefaultClient EVMClient
@@ -1755,3 +1827,8 @@ func (e *EthereumMultinodeClient) WaitForEvents() error {
 func (e *EthereumMultinodeClient) ErrorReason(b ethereum.ContractCaller, tx *types.Transaction, receipt *types.Receipt) (string, error) {
 	return e.DefaultClient.ErrorReason(b, tx, receipt)
 }
+
+// InitializeHeaderSubscription initializes either subscription-based or polling-based header processing
+func (e *EthereumMultinodeClient) InitializeHeaderSubscription() error {
+	return e.DefaultClient.InitializeHeaderSubscription()
+}