Fix simulated failure issue

Before all transactions were processed and where the failure was
simulated a message was printed and all the transactions still
processed. Now the store actually panics but the panic is recovered and
the context is stopped and a graceful shutdown is performed so that
listening can be resumed properly.

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

Author: twoGiants

off_chain_data/application-go/listen.go

@@ -44,16 +44,20 @@ func listen(clientConnection *grpc.ClientConn) {
 	}
 
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	stopCalled := false
 	defer func() {
-		stop()
-		fmt.Println("Context closed.")
+		if !stopCalled {
+			stop()
+			stopCalled = true
+			fmt.Println("Context closed.")
+		}
 	}()
 
 	network := gateway.GetNetwork(channelName)
 	blocks, err := network.BlockEvents(
 		ctx,
-		client.WithCheckpoint(checkpointer),
 		client.WithStartBlock(0), // Used only if there is no checkpoint block number
+		client.WithCheckpoint(checkpointer),
 	)
 	if err != nil {
 		panic(err)
@@ -64,6 +68,18 @@ func listen(clientConnection *grpc.ClientConn) {
 
 	go func() {
 		defer wg.Done()
+		defer func() {
+			msg := "[expected error]: simulated write failure"
+			r := recover()
+			v, ok := r.(string)
+			if ok && v == msg {
+				if !stopCalled {
+					stop()
+					stopCalled = true
+					fmt.Println("Context closed after simulated write failure.")
+				}
+			}
+		}()
 
 		for blockProto := range blocks {
 			select {

off_chain_data/application-go/store/flatFille.go

@@ -2,7 +2,6 @@ package store
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"math"
 	"offChainData/utils"
@@ -18,14 +17,10 @@ var transactionCount uint = 0 // Used only to simulate failures
 // 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) {
-	if err := simulateFailureIfRequired(); err != nil {
-		fmt.Println("[expected error]: " + err.Error())
-		return
-	}
+	simulateFailureIfRequired()
 
 	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)
@@ -49,15 +44,13 @@ func ApplyWritesToOffChainStore(data LedgerUpdate) {
 	}
 }
 
-func simulateFailureIfRequired() error {
+func simulateFailureIfRequired() {
 	if SimulatedFailureCount > 0 && transactionCount >= SimulatedFailureCount {
 		transactionCount = 0
-		return errors.New("simulated write failure")
+		panic("[expected error]: simulated write failure")
 	}
 
 	transactionCount += 1
-
-	return nil
 }
 
 func getSimulatedFailureCount() uint {