Fix simulated failure issue

Before all transactions were processed and when the failure was
simulated a message was printed and all the transactions still
processed. Now the store returns an error when the failure is simulated
which the listener expects so that it can gracefully shutdown the system
and close the context. The context must be closed correctly or the
checkpointer won't save the last processed transactionId to the file
system.

Signed-off-by: Stanislav Jakuschevskij <stas@two-giants.com>

off_chain_data/application-go/listen.go

@@ -43,17 +43,20 @@ func listen(clientConnection *grpc.ClientConn) {
 		fmt.Printf("Simulating a write failure every %d transactions\n", store.SimulatedFailureCount)
 	}
 
-	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	ctx, close := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer func() {
-		stop()
+		close()
 		fmt.Println("Context closed.")
 	}()
 
 	network := gateway.GetNetwork(channelName)
 	blocks, err := network.BlockEvents(
 		ctx,
+		// Used only if there is no checkpoint block number.
+		// Order matters. WithStartBlock must be set before
+		// WithCheckpoint to work.
+		client.WithStartBlock(0),
 		client.WithCheckpoint(checkpointer),
-		client.WithStartBlock(0), // Used only if there is no checkpoint block number
 	)
 	if err != nil {
 		panic(err)
@@ -76,11 +79,15 @@ func listen(clientConnection *grpc.ClientConn) {
 					store.ApplyWritesToOffChainStore,
 					channelName,
 				)
-				blockProcessor.Process()
+
+				if err := blockProcessor.Process(); err == store.ErrExpected {
+					fmt.Println(err)
+					return
+				}
 			}
 		}
 	}()
 
 	wg.Wait()
-	fmt.Println("\nReceived 'SIGTERM' signal. Shutting down listener gracefully...")
+	fmt.Println("\nShutting down listener gracefully...")
 }

off_chain_data/application-go/processor/block.go

@@ -29,7 +29,7 @@ func NewBlock(
 	}
 }
 
-func (b *block) Process() {
+func (b *block) Process() error {
 	blockNumber := b.parsedBlock.Number()
 
 	fmt.Println("\nReceived block", blockNumber)
@@ -42,13 +42,17 @@ func (b *block) Process() {
 			b.writeToStore,
 			b.channelName,
 		}
-		aTransaction.process()
+		if err := aTransaction.process(); err != nil {
+			return err
+		}
 
 		transactionId := validTransaction.ChannelHeader().GetTxId()
 		b.checkpointer.CheckpointTransaction(blockNumber, transactionId)
 	}
 
 	b.checkpointer.CheckpointBlock(b.parsedBlock.Number())
+
+	return nil
 }
 
 func (b *block) validTransactions() []*parser.Transaction {

off_chain_data/application-go/processor/transaction.go

@@ -14,22 +14,25 @@ type transaction struct {
 	channelName  string
 }
 
-func (t *transaction) process() {
+func (t *transaction) process() error {
 	transactionId := t.transaction.ChannelHeader().GetTxId()
 
 	writes := t.writes()
 	if len(writes) == 0 {
 		fmt.Println("Skipping read-only or system transaction", transactionId)
-		return
+		return nil
 	}
 
 	fmt.Println("Process transaction", transactionId)
 
-	t.writeToStore(store.LedgerUpdate{
+	if err := t.writeToStore(store.LedgerUpdate{
 		BlockNumber:   t.blockNumber,
 		TransactionId: transactionId,
 		Writes:        writes,
-	})
+	}); err != nil {
+		return err
+	}
+	return nil
 }
 
 func (t *transaction) writes() []store.Write {

off_chain_data/application-go/store/flatFille.go

@@ -14,18 +14,17 @@ import (
 var storeFile = utils.EnvOrDefault("STORE_FILE", "store.log")
 var SimulatedFailureCount = getSimulatedFailureCount()
 var transactionCount uint = 0 // Used only to simulate failures
+var ErrExpected = errors.New("[expected error]: simulated write failure")
 
 // Apply writes for a given transaction to off-chain data store, ideally in a single operation for fault tolerance.
 // This implementation just writes to a file.
-func ApplyWritesToOffChainStore(data LedgerUpdate) {
+func ApplyWritesToOffChainStore(data LedgerUpdate) error {
 	if err := simulateFailureIfRequired(); err != nil {
-		fmt.Println("[expected error]: " + err.Error())
-		return
+		return err
 	}
 
 	writes := []string{}
 	for _, write := range data.Writes {
-		// TODO write also the TxID and block number so that you can compare easier to the output
 		marshaled, err := json.Marshal(write)
 		if err != nil {
 			panic(err)
@@ -47,12 +46,14 @@ func ApplyWritesToOffChainStore(data LedgerUpdate) {
 	if err := f.Close(); err != nil {
 		panic(err)
 	}
+
+	return nil
 }
 
 func simulateFailureIfRequired() error {
 	if SimulatedFailureCount > 0 && transactionCount >= SimulatedFailureCount {
 		transactionCount = 0
-		return errors.New("simulated write failure")
+		return ErrExpected
 	}
 
 	transactionCount += 1

off_chain_data/application-go/store/model.go

@@ -1,7 +1,7 @@
 package store
 
 // Apply writes for a given transaction to off-chain data store, ideally in a single operation for fault tolerance.
-type Writer = func(data LedgerUpdate)
+type Writer = func(data LedgerUpdate) error
 
 // Ledger update made by a specific transaction.
 type LedgerUpdate struct {