Implement store

Persisting ledger writes to the file system into the store.log file in
the application-go directory. The write values are converted from bytes
to a string when the read write sets are unwrapped in the transaction
processor.

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

off_chain_data/application-go/listen.go

@@ -2,18 +2,28 @@ package main
 
 import (
 	"context"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"math"
 	"offChainData/parser"
+	"os"
 	"slices"
 	"strconv"
+	"strings"
 
 	"github.com/hyperledger/fabric-gateway/pkg/client"
 	"google.golang.org/grpc"
 )
 
 var checkpointFile = envOrDefault("CHECKPOINT_FILE", "checkpoint.json")
+var storeFile = envOrDefault("STORE_FILE", "store.log")
 var simulatedFailureCount = getSimulatedFailureCount()
+
+const startBlock = 0
+
+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.
 type store = func(data ledgerUpdate)
 
@@ -27,20 +37,59 @@ type ledgerUpdate struct {
 // Description of a ledger write that can be applied to an off-chain data store.
 type write struct {
 	// Channel whose ledger is being updated.
-	channelName string
+	ChannelName string `json:"channelName"`
 	// Namespace within the ledger.
-	namespace string
+	Namespace string `json:"namespace"`
 	// Key name within the ledger namespace.
-	key string
+	Key string `json:"key"`
 	// Whether the key and associated value are being deleted.
-	isDelete bool
-	// If `isDelete` is false, the value written to the key; otherwise ignored.
-	value []byte
+	IsDelete bool `json:"isDelete"`
+	// If `isDelete` is false, the Value written to the key; otherwise ignored.
+	Value string `json:"value"`
 }
 
 // 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.
 var applyWritesToOffChainStore = func(data ledgerUpdate) {
+	if err := simulateFailureIfRequired(); err != nil {
+		fmt.Println("[expected error]: " + err.Error())
+		return
+	}
+
+	writes := []string{}
+	for _, write := range data.writes {
+		marshaled, err := json.Marshal(write)
+		if err != nil {
+			panic(err)
+		}
+
+		writes = append(writes, string(marshaled))
+	}
+
+	f, err := os.OpenFile(storeFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		panic(err)
+	}
+
+	if _, err := f.Write([]byte(strings.Join(writes, "\n") + "\n")); err != nil {
+		f.Close()
+		panic(err)
+	}
+
+	if err := f.Close(); err != nil {
+		panic(err)
+	}
+}
+
+func simulateFailureIfRequired() error {
+	if simulatedFailureCount > 0 && transactionCount >= simulatedFailureCount {
+		transactionCount = 0
+		return errors.New("simulated write failure")
+	}
+
+	transactionCount += 1
+
+	return nil
 }
 
 func listen(clientConnection *grpc.ClientConn) {
@@ -62,7 +111,7 @@ func listen(clientConnection *grpc.ClientConn) {
 	fmt.Printf("Start event listening from block %d\n", checkpointer.BlockNumber())
 	fmt.Printf("Last processed transaction ID within block: %s\n", checkpointer.TransactionID())
 	if simulatedFailureCount > 0 {
-		fmt.Printf("Simulating a write failure every %d transactions", simulatedFailureCount)
+		fmt.Printf("Simulating a write failure every %d transactions\n", simulatedFailureCount)
 	}
 
 	// TODO put into infinite loop like in public docs example
@@ -71,8 +120,8 @@ func listen(clientConnection *grpc.ClientConn) {
 
 	blocks, err := network.BlockEvents(
 		ctx,
-		client.WithStartBlock(0),
 		client.WithCheckpoint(checkpointer),
+		client.WithStartBlock(startBlock), // Used only if there is no checkpoint block number
 	)
 	if err != nil {
 		panic(err)
@@ -200,8 +249,6 @@ type transactionProcessor struct {
 func (t *transactionProcessor) process() {
 	transactionId := t.transaction.ChannelHeader().GetTxId()
 
-	fmt.Println("Process transaction", transactionId)
-
 	writes := t.writes()
 	if len(writes) == 0 {
 		fmt.Println("Skipping read-only or system transaction", transactionId)
@@ -232,14 +279,13 @@ func (t *transactionProcessor) writes() []write {
 		namespace := readWriteSet.Namespace()
 
 		for _, kvWrite := range readWriteSet.ReadWriteSet().GetWrites() {
-			aWrite := write{
+			writes = append(writes, write{
 				channelName,
 				namespace,
 				kvWrite.GetKey(),
 				kvWrite.GetIsDelete(),
-				kvWrite.GetValue(),
-			}
-			writes = append(writes, aWrite)
+				string(kvWrite.GetValue()), // Convert bytes to text, purely for readability in output
+			})
 		}
 	}
 

off_chain_data/application-go/transact.go

@@ -36,7 +36,7 @@ func newTransactApp(smartContract *atb.AssetTransferBasic) *transactApp {
 
 func (t *transactApp) run() {
 	for i := 0; i < int(t.batchSize); i++ {
-		go t.transact()
+		t.transact()
 	}
 }