Replace panic with error handling

Starting from the processor.Block.Process all methods now return errors
if something goes wrong with unpacking of the blocks and reading the
transactions. In each function where the error is being propagated back
to client it is wrapped in a message with the function name. This makes
it easier to track down the error and see the propagation chain. Finally
the error is logged to the terminal and the go routine shuts down
gracefully. The graceful shutdown executes all deferred functions which
close the context, the checkpointer and the gateway.

Before panics were used everywhere which was an issue because the
unpacking of the blocks happened in a go routine. When a panic happens
in a go routine only the deferred functions of the go routine are called
but not those of the client which lead to unexpected behavior.

The transact function is also executed in a go routine therefore the
same typo of error handling was implemented there.

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

off_chain_data/application-go/contract/contract.go

@@ -6,6 +6,7 @@
 package contract
 
 import (
+	"fmt"
 	"strconv"
 
 	"github.com/hyperledger/fabric-gateway/pkg/client"
@@ -19,7 +20,7 @@ func NewAssetTransferBasic(contract *client.Contract) *AssetTransferBasic {
 	return &AssetTransferBasic{contract}
 }
 
-func (atb *AssetTransferBasic) CreateAsset(anAsset Asset) {
+func (atb *AssetTransferBasic) CreateAsset(anAsset Asset) error {
 	if _, err := atb.contract.Submit(
 		"CreateAsset",
 		client.WithArguments(
@@ -29,11 +30,12 @@ func (atb *AssetTransferBasic) CreateAsset(anAsset Asset) {
 			anAsset.Owner,
 			strconv.FormatUint(anAsset.AppraisedValue, 10),
 		)); err != nil {
-		panic(err)
+		return fmt.Errorf("in CreateAsset: %w", err)
 	}
+	return nil
 }
 
-func (atb *AssetTransferBasic) TransferAsset(id, newOwner string) string {
+func (atb *AssetTransferBasic) TransferAsset(id, newOwner string) (string, error) {
 	result, err := atb.contract.Submit(
 		"TransferAsset",
 		client.WithArguments(
@@ -42,27 +44,28 @@ func (atb *AssetTransferBasic) TransferAsset(id, newOwner string) string {
 		),
 	)
 	if err != nil {
-		panic(err)
+		return "", fmt.Errorf("in TransferAsset: %w", err)
 	}
 
-	return string(result)
+	return string(result), nil
 }
 
-func (atb *AssetTransferBasic) DeleteAsset(id string) {
+func (atb *AssetTransferBasic) DeleteAsset(id string) error {
 	if _, err := atb.contract.Submit(
 		"DeleteAsset",
 		client.WithArguments(
 			id,
 		),
 	); err != nil {
-		panic(err)
+		return fmt.Errorf("in DeleteAsset: %w", err)
 	}
+	return nil
 }
 
-func (atb *AssetTransferBasic) GetAllAssets() []byte {
+func (atb *AssetTransferBasic) GetAllAssets() ([]byte, error) {
 	result, err := atb.contract.Evaluate("GetAllAssets")
 	if err != nil {
-		panic(err)
+		return []byte{}, fmt.Errorf("in GetAllAssets: %w", err)
 	}
-	return result
+	return result, nil
 }

off_chain_data/application-go/getAllAssets.go

@@ -26,7 +26,10 @@ func getAllAssets(clientConnection *grpc.ClientConn) {
 
 	contract := gateway.GetNetwork(channelName).GetContract(chaincodeName)
 	smartContract := atb.NewAssetTransferBasic(contract)
-	assets := smartContract.GetAllAssets()
+	assets, err := smartContract.GetAllAssets()
+	if err != nil {
+		panic((err))
+	}
 
 	fmt.Println(formatJSON(assets))
 }

off_chain_data/application-go/listen.go

@@ -80,8 +80,8 @@ func listen(clientConnection *grpc.ClientConn) {
 					channelName,
 				)
 
-				if err := blockProcessor.Process(); err == store.ErrExpected {
-					fmt.Println(err)
+				if err := blockProcessor.Process(); err != nil {
+					fmt.Println("\033[31m[ERROR]\033[0m", err)
 					return
 				}
 			}

off_chain_data/application-go/parser/block.go

@@ -14,74 +14,102 @@ type Block struct {
 }
 
 func ParseBlock(block *common.Block) *Block {
-	return &Block{block, nil}
+	return &Block{block, []*Transaction{}}
 }
 
-func (b *Block) Number() uint64 {
-	header := utils.AssertDefined(b.block.GetHeader(), "missing block header")
-	return header.GetNumber()
+func (b *Block) Number() (uint64, error) {
+	header, err := utils.AssertDefined(b.block.GetHeader(), "missing block header")
+	if err != nil {
+		return 0, fmt.Errorf("in Number: %w", err)
+	}
+	return header.GetNumber(), nil
 }
 
-func (b *Block) Transactions() []*Transaction {
-	return utils.Cache(func() []*Transaction {
-		envelopes := b.unmarshalEnvelopesFromBlockData()
+func (b *Block) Transactions() ([]*Transaction, error) {
+	return utils.Cache(func() ([]*Transaction, error) {
+		funcName := "Transactions"
+		envelopes, err := b.unmarshalEnvelopesFromBlockData()
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		commonPayloads := b.unmarshalPayloadsFrom(envelopes)
+		commonPayloads, err := b.unmarshalPayloadsFrom(envelopes)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		payloads := b.parse(commonPayloads)
+		payloads, err := b.parse(commonPayloads)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		return b.createTransactionsFrom(payloads)
+		return b.createTransactionsFrom(payloads), nil
 	})()
 }
 
-func (b *Block) unmarshalEnvelopesFromBlockData() []*common.Envelope {
+func (b *Block) unmarshalEnvelopesFromBlockData() ([]*common.Envelope, error) {
 	result := []*common.Envelope{}
 	for _, blockData := range b.block.GetData().GetData() {
 		envelope := &common.Envelope{}
 		if err := proto.Unmarshal(blockData, envelope); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in unmarshalEnvelopesFromBlockData: %w", err)
 		}
 		result = append(result, envelope)
 	}
-	return result
+	return result, nil
 }
 
-func (*Block) unmarshalPayloadsFrom(envelopes []*common.Envelope) []*common.Payload {
+func (*Block) unmarshalPayloadsFrom(envelopes []*common.Envelope) ([]*common.Payload, error) {
 	result := []*common.Payload{}
 	for _, envelope := range envelopes {
 		commonPayload := &common.Payload{}
 		if err := proto.Unmarshal(envelope.GetPayload(), commonPayload); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in unmarshalPayloadsFrom: %w", err)
 		}
 		result = append(result, commonPayload)
 	}
-	return result
+	return result, nil
 }
 
-func (b *Block) parse(commonPayloads []*common.Payload) []*payload {
-	validationCodes := b.extractTransactionValidationCodes()
+func (b *Block) parse(commonPayloads []*common.Payload) ([]*payload, error) {
+	funcName := "parse"
+
+	validationCodes, err := b.extractTransactionValidationCodes()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+
 	result := []*payload{}
 	for i, commonPayload := range commonPayloads {
-		payload := parsePayload(
-			commonPayload,
-			int32(utils.AssertDefined(
-				validationCodes[i],
-				fmt.Sprint("missing validation code index", i),
-			),
-			),
+		statusCode, err := utils.AssertDefined(
+			validationCodes[i],
+			fmt.Sprint("missing validation code index", i),
 		)
-		if payload.isEndorserTransaction() {
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
+
+		payload := parsePayload(commonPayload, int32(statusCode))
+		is, err := payload.isEndorserTransaction()
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
+		if is {
 			result = append(result, payload)
 		}
 	}
-	return result
+
+	return result, nil
 }
 
-func (b *Block) extractTransactionValidationCodes() []byte {
-	metadata := utils.AssertDefined(
+func (b *Block) extractTransactionValidationCodes() ([]byte, error) {
+	metadata, err := utils.AssertDefined(
 		b.block.GetMetadata(),
 		"missing block metadata",
 	)
+	if err != nil {
+		return nil, fmt.Errorf("in extractTransactionValidationCodes: %w", err)
+	}
 
 	return utils.AssertDefined(
 		metadata.GetMetadata()[common.BlockMetadataIndex_TRANSACTIONS_FILTER],

off_chain_data/application-go/parser/block_test.go

@@ -35,12 +35,17 @@ func Test_GetReadWriteSetsFromEndorserTransaction(t *testing.T) {
 	}
 
 	parsedEndorserTransaction := parseEndorserTransaction(transaction)
-	if len(parsedEndorserTransaction.readWriteSets()) != 1 {
-		t.Fatal("expected 1 ReadWriteSet, got", len(parsedEndorserTransaction.readWriteSets()))
+	readWriteSets, err := parsedEndorserTransaction.readWriteSets()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if len(readWriteSets) != 1 {
+		t.Fatal("expected 1 ReadWriteSet, got", len(readWriteSets))
 	}
 
 	assertReadWriteSet(
-		parsedEndorserTransaction.readWriteSets()[0].namespaceReadWriteSets()[0],
+		readWriteSets[0].namespaceReadWriteSets()[0],
 		expectedNamespace,
 		expectedAsset,
 		t,
@@ -57,7 +62,10 @@ func assertReadWriteSet(
 		t.Errorf("expected namespace %s, got %s", expectedNamespace, parsedNsRwSet.Namespace())
 	}
 
-	actualKVRWSet := parsedNsRwSet.ReadWriteSet()
+	actualKVRWSet, err := parsedNsRwSet.ReadWriteSet()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
 	if len(actualKVRWSet.Writes) != 1 {
 		t.Fatal("expected 1 write, got", len(actualKVRWSet.Writes))
 	}

off_chain_data/application-go/parser/endorserTransaction.go

@@ -1,6 +1,7 @@
 package parser
 
 import (
+	"fmt"
 	"offChainData/utils"
 
 	"github.com/hyperledger/fabric-protos-go-apiv2/ledger/rwset"
@@ -16,83 +17,104 @@ func parseEndorserTransaction(transaction *peer.Transaction) *endorserTransactio
 	return &endorserTransaction{transaction}
 }
 
-func (p *endorserTransaction) readWriteSets() []*readWriteSet {
-	return utils.Cache(func() []*readWriteSet {
-		chaincodeActionPayloads := p.unmarshalChaincodeActionPayloads()
+func (p *endorserTransaction) readWriteSets() ([]*readWriteSet, error) {
+	return utils.Cache(func() ([]*readWriteSet, error) {
+		funcName := "readWriteSets"
+		chaincodeActionPayloads, err := p.unmarshalChaincodeActionPayloads()
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		chaincodeEndorsedActions := p.extractChaincodeEndorsedActionsFrom(chaincodeActionPayloads)
+		chaincodeEndorsedActions, err := p.extractChaincodeEndorsedActionsFrom(chaincodeActionPayloads)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		proposalResponsePayloads := p.unmarshalProposalResponsePayloadsFrom(chaincodeEndorsedActions)
+		proposalResponsePayloads, err := p.unmarshalProposalResponsePayloadsFrom(chaincodeEndorsedActions)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		chaincodeActions := p.unmarshalChaincodeActionsFrom(proposalResponsePayloads)
+		chaincodeActions, err := p.unmarshalChaincodeActionsFrom(proposalResponsePayloads)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		txReadWriteSets := p.unmarshalTxReadWriteSetsFrom(chaincodeActions)
+		txReadWriteSets, err := p.unmarshalTxReadWriteSetsFrom(chaincodeActions)
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
-		return p.parseReadWriteSets(txReadWriteSets)
+		return p.parseReadWriteSets(txReadWriteSets), nil
 	})()
 }
 
-func (p *endorserTransaction) unmarshalChaincodeActionPayloads() []*peer.ChaincodeActionPayload {
+func (p *endorserTransaction) unmarshalChaincodeActionPayloads() ([]*peer.ChaincodeActionPayload, error) {
 	result := []*peer.ChaincodeActionPayload{}
 	for _, transactionAction := range p.transaction.GetActions() {
 		chaincodeActionPayload := &peer.ChaincodeActionPayload{}
 		if err := proto.Unmarshal(transactionAction.GetPayload(), chaincodeActionPayload); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in unmarshalChaincodeActionPayloads: %w", err)
 		}
 
 		result = append(result, chaincodeActionPayload)
 	}
-	return result
+	return result, nil
 }
 
-func (*endorserTransaction) extractChaincodeEndorsedActionsFrom(chaincodeActionPayloads []*peer.ChaincodeActionPayload) []*peer.ChaincodeEndorsedAction {
+func (*endorserTransaction) extractChaincodeEndorsedActionsFrom(chaincodeActionPayloads []*peer.ChaincodeActionPayload) ([]*peer.ChaincodeEndorsedAction, error) {
 	result := []*peer.ChaincodeEndorsedAction{}
 	for _, payload := range chaincodeActionPayloads {
+		chaincodeEndorsedAction, err := utils.AssertDefined(
+			payload.GetAction(),
+			"missing chaincode endorsed action",
+		)
+		if err != nil {
+			return nil, fmt.Errorf("in extractChaincodeEndorsedActionsFrom: %w", err)
+		}
+
 		result = append(
 			result,
-			utils.AssertDefined(
-				payload.GetAction(),
-				"missing chaincode endorsed action",
-			),
+			chaincodeEndorsedAction,
 		)
 	}
-	return result
+	return result, nil
 }
 
-func (*endorserTransaction) unmarshalProposalResponsePayloadsFrom(chaincodeEndorsedActions []*peer.ChaincodeEndorsedAction) []*peer.ProposalResponsePayload {
+func (*endorserTransaction) unmarshalProposalResponsePayloadsFrom(chaincodeEndorsedActions []*peer.ChaincodeEndorsedAction) ([]*peer.ProposalResponsePayload, error) {
 	result := []*peer.ProposalResponsePayload{}
 	for _, endorsedAction := range chaincodeEndorsedActions {
 		proposalResponsePayload := &peer.ProposalResponsePayload{}
 		if err := proto.Unmarshal(endorsedAction.GetProposalResponsePayload(), proposalResponsePayload); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in unmarshalProposalResponsePayloadsFrom: %w", err)
 		}
 		result = append(result, proposalResponsePayload)
 	}
-	return result
+	return result, nil
 }
 
-func (*endorserTransaction) unmarshalChaincodeActionsFrom(proposalResponsePayloads []*peer.ProposalResponsePayload) []*peer.ChaincodeAction {
+func (*endorserTransaction) unmarshalChaincodeActionsFrom(proposalResponsePayloads []*peer.ProposalResponsePayload) ([]*peer.ChaincodeAction, error) {
 	result := []*peer.ChaincodeAction{}
 	for _, proposalResponsePayload := range proposalResponsePayloads {
 		chaincodeAction := &peer.ChaincodeAction{}
 		if err := proto.Unmarshal(proposalResponsePayload.GetExtension(), chaincodeAction); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in unmarshalChaincodeActionsFrom: %w", err)
 		}
 		result = append(result, chaincodeAction)
 	}
-	return result
+	return result, nil
 }
 
-func (*endorserTransaction) unmarshalTxReadWriteSetsFrom(chaincodeActions []*peer.ChaincodeAction) []*rwset.TxReadWriteSet {
+func (*endorserTransaction) unmarshalTxReadWriteSetsFrom(chaincodeActions []*peer.ChaincodeAction) ([]*rwset.TxReadWriteSet, error) {
 	result := []*rwset.TxReadWriteSet{}
 	for _, chaincodeAction := range chaincodeActions {
 		txReadWriteSet := &rwset.TxReadWriteSet{}
 		if err := proto.Unmarshal(chaincodeAction.GetResults(), txReadWriteSet); err != nil {
-			continue
+			return nil, fmt.Errorf("in unmarshalTxReadWriteSetsFrom: %w", err)
 		}
 		result = append(result, txReadWriteSet)
 	}
-	return result
+	return result, nil
 }
 
 func (*endorserTransaction) parseReadWriteSets(txReadWriteSets []*rwset.TxReadWriteSet) []*readWriteSet {

off_chain_data/application-go/parser/namespaceReadWriteSet.go

@@ -1,6 +1,7 @@
 package parser
 
 import (
+	"fmt"
 	"offChainData/utils"
 
 	"github.com/hyperledger/fabric-protos-go-apiv2/ledger/rwset"
@@ -20,13 +21,13 @@ func (p *NamespaceReadWriteSet) Namespace() string {
 	return p.nsReadWriteSet.GetNamespace()
 }
 
-func (p *NamespaceReadWriteSet) ReadWriteSet() *kvrwset.KVRWSet {
-	return utils.Cache(func() *kvrwset.KVRWSet {
+func (p *NamespaceReadWriteSet) ReadWriteSet() (*kvrwset.KVRWSet, error) {
+	return utils.Cache(func() (*kvrwset.KVRWSet, error) {
 		result := kvrwset.KVRWSet{}
 		if err := proto.Unmarshal(p.nsReadWriteSet.GetRwset(), &result); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in ReadWriteSet: %w", err)
 		}
 
-		return &result
+		return &result, nil
 	})()
 }

off_chain_data/application-go/parser/payload.go

@@ -18,34 +18,54 @@ func parsePayload(commonPayload *common.Payload, statusCode int32) *payload {
 	return &payload{commonPayload, statusCode}
 }
 
-func (p *payload) channelHeader() *common.ChannelHeader {
-	return utils.Cache(func() *common.ChannelHeader {
-		header := utils.AssertDefined(p.commonPayload.GetHeader(), "missing payload header")
+func (p *payload) channelHeader() (*common.ChannelHeader, error) {
+	return utils.Cache(func() (*common.ChannelHeader, error) {
+		funcName := "channelHeader"
+
+		header, err := utils.AssertDefined(p.commonPayload.GetHeader(), "missing payload header")
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
 
 		result := &common.ChannelHeader{}
 		if err := proto.Unmarshal(header.GetChannelHeader(), result); err != nil {
-			panic(err)
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
 		}
 
-		return result
+		return result, nil
 	})()
 }
 
-func (p *payload) endorserTransaction() *endorserTransaction {
-	if !p.isEndorserTransaction() {
-		panic(fmt.Errorf("unexpected payload type: %d", p.channelHeader().GetType()))
+func (p *payload) endorserTransaction() (*endorserTransaction, error) {
+	funcName := "endorserTransaction"
+
+	is, err := p.isEndorserTransaction()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+	if !is {
+		channelHeader, err := p.channelHeader()
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
+		return nil, fmt.Errorf("unexpected payload type: %d", channelHeader.GetType())
 	}
 
 	result := &peer.Transaction{}
 	if err := proto.Unmarshal(p.commonPayload.GetData(), result); err != nil {
-		panic(err)
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
 	}
 
-	return parseEndorserTransaction(result)
+	return parseEndorserTransaction(result), nil
 }
 
-func (p *payload) isEndorserTransaction() bool {
-	return p.channelHeader().GetType() == int32(common.HeaderType_ENDORSER_TRANSACTION)
+func (p *payload) isEndorserTransaction() (bool, error) {
+	channelHeader, err := p.channelHeader()
+	if err != nil {
+		return false, fmt.Errorf("in isEndorserTransaction: %w", err)
+	}
+
+	return channelHeader.GetType() == int32(common.HeaderType_ENDORSER_TRANSACTION), nil
 }
 
 func (p *payload) isValid() bool {

off_chain_data/application-go/parser/transaction.go

@@ -1,6 +1,8 @@
 package parser
 
 import (
+	"fmt"
+
 	"github.com/hyperledger/fabric-protos-go-apiv2/common"
 )
 
@@ -12,17 +14,29 @@ func newTransaction(payload *payload) *Transaction {
 	return &Transaction{payload}
 }
 
-func (t *Transaction) ChannelHeader() *common.ChannelHeader {
+func (t *Transaction) ChannelHeader() (*common.ChannelHeader, error) {
 	return t.payload.channelHeader()
 }
 
-func (t *Transaction) NamespaceReadWriteSets() []*NamespaceReadWriteSet {
+func (t *Transaction) NamespaceReadWriteSets() ([]*NamespaceReadWriteSet, error) {
+	funcName := "NamespaceReadWriteSets"
+
+	endorserTransaction, err := t.payload.endorserTransaction()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+
+	txReadWriteSets, err := endorserTransaction.readWriteSets()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+
 	result := []*NamespaceReadWriteSet{}
-	for _, readWriteSet := range t.payload.endorserTransaction().readWriteSets() {
+	for _, readWriteSet := range txReadWriteSets {
 		result = append(result, readWriteSet.namespaceReadWriteSets()...)
 	}
 
-	return result
+	return result, nil
 }
 
 func (t *Transaction) IsValid() bool {

off_chain_data/application-go/processor/block.go

@@ -30,11 +30,21 @@ func NewBlock(
 }
 
 func (b *block) Process() error {
-	blockNumber := b.parsedBlock.Number()
+	funcName := "Process"
+
+	blockNumber, err := b.parsedBlock.Number()
+	if err != nil {
+		return fmt.Errorf("in %s: %w", funcName, err)
+	}
 
 	fmt.Println("\nReceived block", blockNumber)
 
-	for _, validTransaction := range b.validTransactions() {
+	validTransactions, err := b.validTransactions()
+	if err != nil {
+		return fmt.Errorf("in %s: %w", funcName, err)
+	}
+
+	for _, validTransaction := range validTransactions {
 		aTransaction := transaction{
 			blockNumber,
 			validTransaction,
@@ -43,46 +53,74 @@ func (b *block) Process() error {
 			b.channelName,
 		}
 		if err := aTransaction.process(); err != nil {
-			return err
+			return fmt.Errorf("in %s: %w", funcName, err)
 		}
 
-		transactionId := validTransaction.ChannelHeader().GetTxId()
+		channelHeader, err := validTransaction.ChannelHeader()
+		if err != nil {
+			return fmt.Errorf("in %s: %w", funcName, err)
+		}
+		transactionId := channelHeader.GetTxId()
 		b.checkpointer.CheckpointTransaction(blockNumber, transactionId)
 	}
 
-	b.checkpointer.CheckpointBlock(b.parsedBlock.Number())
+	b.checkpointer.CheckpointBlock(blockNumber)
 
 	return nil
 }
 
-func (b *block) validTransactions() []*parser.Transaction {
+func (b *block) validTransactions() ([]*parser.Transaction, error) {
 	result := []*parser.Transaction{}
-	for _, transaction := range b.getNewTransactions() {
+	newTransactions, err := b.getNewTransactions()
+	if err != nil {
+		return nil, fmt.Errorf("in validTransactions: %w", err)
+	}
+
+	for _, transaction := range newTransactions {
 		if transaction.IsValid() {
 			result = append(result, transaction)
 		}
 	}
-	return result
+	return result, nil
 }
 
-func (b *block) getNewTransactions() []*parser.Transaction {
-	transactions := b.parsedBlock.Transactions()
+func (b *block) getNewTransactions() ([]*parser.Transaction, error) {
+	funcName := "getNewTransactions"
+
+	transactions, err := b.parsedBlock.Transactions()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
 
 	lastTransactionId := b.checkpointer.TransactionID()
 	if lastTransactionId == "" {
 		// No previously processed transactions within this block so all are new
-		return transactions
+		return transactions, nil
 	}
 
 	// Ignore transactions up to the last processed transaction ID
-	lastProcessedIndex := b.findLastProcessedIndex()
-	return transactions[lastProcessedIndex+1:]
+	lastProcessedIndex, err := b.findLastProcessedIndex()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+	return transactions[lastProcessedIndex+1:], nil
 }
 
-func (b *block) findLastProcessedIndex() int {
+func (b *block) findLastProcessedIndex() (int, error) {
+	funcName := "findLastProcessedIndex"
+
+	transactions, err := b.parsedBlock.Transactions()
+	if err != nil {
+		return 0, fmt.Errorf("in %s: %w", funcName, err)
+	}
+
 	blockTransactionIds := []string{}
-	for _, transaction := range b.parsedBlock.Transactions() {
-		blockTransactionIds = append(blockTransactionIds, transaction.ChannelHeader().GetTxId())
+	for _, transaction := range transactions {
+		channelHeader, err := transaction.ChannelHeader()
+		if err != nil {
+			return 0, fmt.Errorf("in %s: %w", funcName, err)
+		}
+		blockTransactionIds = append(blockTransactionIds, channelHeader.GetTxId())
 	}
 
 	lastTransactionId := b.checkpointer.TransactionID()
@@ -92,27 +130,18 @@ func (b *block) findLastProcessedIndex() int {
 			lastProcessedIndex = index
 		}
 	}
+
 	if lastProcessedIndex < 0 {
-		panic(
-			fmt.Errorf(
-				"checkpoint transaction ID %s not found in block %d containing transactions: %s",
-				lastTransactionId,
-				b.parsedBlock.Number(),
-				b.joinByComma(blockTransactionIds),
-			),
+		blockNumber, err := b.parsedBlock.Number()
+		if err != nil {
+			return 0, fmt.Errorf("in %s: %w", funcName, err)
+		}
+		return lastProcessedIndex, newTxIdNotFoundError(
+			lastTransactionId,
+			blockNumber,
+			blockTransactionIds,
 		)
 	}
-	return lastProcessedIndex
-}
 
-func (b *block) joinByComma(list []string) string {
-	result := ""
-	for index, item := range list {
-		if len(list)-1 == index {
-			result += item
-		} else {
-			result += item + ", "
-		}
-	}
-	return result
+	return lastProcessedIndex, nil
 }

off_chain_data/application-go/processor/transaction.go

@@ -15,9 +15,19 @@ type transaction struct {
 }
 
 func (t *transaction) process() error {
-	transactionId := t.transaction.ChannelHeader().GetTxId()
+	funcName := "process"
+
+	channelHeader, err := t.transaction.ChannelHeader()
+	if err != nil {
+		return fmt.Errorf("in %s: %w", funcName, err)
+	}
+	transactionId := channelHeader.GetTxId()
+
+	writes, err := t.writes()
+	if err != nil {
+		return fmt.Errorf("in %s: %w", funcName, err)
+	}
 
-	writes := t.writes()
 	if len(writes) == 0 {
 		fmt.Println("Skipping read-only or system transaction", transactionId)
 		return nil
@@ -30,18 +40,29 @@ func (t *transaction) process() error {
 		TransactionId: transactionId,
 		Writes:        writes,
 	}); err != nil {
-		return err
+		return fmt.Errorf("in %s: %w", funcName, err)
 	}
+
 	return nil
 }
 
-func (t *transaction) writes() []store.Write {
+func (t *transaction) writes() ([]store.Write, error) {
+	funcName := "writes"
 	// TODO this entire code should live in the parser and just return the kvWrite which
 	// we then map to store.Write and return
-	t.channelName = t.transaction.ChannelHeader().GetChannelId()
+	channelHeader, err := t.transaction.ChannelHeader()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
+	t.channelName = channelHeader.GetChannelId()
+
+	nsReadWriteSets, err := t.transaction.NamespaceReadWriteSets()
+	if err != nil {
+		return nil, fmt.Errorf("in %s: %w", funcName, err)
+	}
 
 	nonSystemCCReadWriteSets := []*parser.NamespaceReadWriteSet{}
-	for _, nsReadWriteSet := range t.transaction.NamespaceReadWriteSets() {
+	for _, nsReadWriteSet := range nsReadWriteSets {
 		if !t.isSystemChaincode(nsReadWriteSet.Namespace()) {
 			nonSystemCCReadWriteSets = append(nonSystemCCReadWriteSets, nsReadWriteSet)
 		}
@@ -51,7 +72,12 @@ func (t *transaction) writes() []store.Write {
 	for _, readWriteSet := range nonSystemCCReadWriteSets {
 		namespace := readWriteSet.Namespace()
 
-		for _, kvWrite := range readWriteSet.ReadWriteSet().GetWrites() {
+		kvReadWriteSet, err := readWriteSet.ReadWriteSet()
+		if err != nil {
+			return nil, fmt.Errorf("in %s: %w", funcName, err)
+		}
+
+		for _, kvWrite := range kvReadWriteSet.GetWrites() {
 			writes = append(writes, store.Write{
 				ChannelName: t.channelName,
 				Namespace:   namespace,
@@ -62,7 +88,7 @@ func (t *transaction) writes() []store.Write {
 		}
 	}
 
-	return writes
+	return writes, nil
 }
 
 func (t *transaction) isSystemChaincode(chaincodeName string) bool {

off_chain_data/application-go/processor/txIdNotFoundError.go

@@ -0,0 +1,32 @@
+package processor
+
+import "fmt"
+
+type txIdNotFoundError struct {
+	txId        string
+	blockNumber uint64
+	blockTxIds  []string
+}
+
+func newTxIdNotFoundError(txId string, blockNumber uint64, blockTxIds []string) *txIdNotFoundError {
+	return &txIdNotFoundError{
+		txId, blockNumber, blockTxIds,
+	}
+}
+
+func (t *txIdNotFoundError) Error() string {
+	format := "checkpoint transaction ID %s not found in block %d containing transactions: %s"
+	return fmt.Sprintf(format, t.txId, t.blockNumber, t.blockTxIdsJoinedByComma())
+}
+
+func (t *txIdNotFoundError) blockTxIdsJoinedByComma() string {
+	result := ""
+	for index, item := range t.blockTxIds {
+		if len(t.blockTxIds)-1 == index {
+			result += item
+		} else {
+			result += item + ", "
+		}
+	}
+	return result
+}

off_chain_data/application-go/store/flatFille.go

@@ -14,20 +14,21 @@ 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) error {
+	funcName := "ApplyWritesToOffChainStore"
+
 	if err := simulateFailureIfRequired(); err != nil {
-		return err
+		return fmt.Errorf("in %s: %w", funcName, err)
 	}
 
 	writes := []string{}
 	for _, write := range data.Writes {
 		marshaled, err := json.Marshal(write)
 		if err != nil {
-			panic(err)
+			return fmt.Errorf("in %s: %w", funcName, err)
 		}
 
 		writes = append(writes, string(marshaled))
@@ -35,16 +36,16 @@ func ApplyWritesToOffChainStore(data LedgerUpdate) error {
 
 	f, err := os.OpenFile(storeFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 	if err != nil {
-		panic(err)
+		return fmt.Errorf("in %s: %w", funcName, err)
 	}
 
 	if _, err := f.Write([]byte(strings.Join(writes, "\n") + "\n")); err != nil {
 		f.Close()
-		panic(err)
+		return fmt.Errorf("in %s: %w", funcName, err)
 	}
 
 	if err := f.Close(); err != nil {
-		panic(err)
+		return fmt.Errorf("in %s: %w", funcName, err)
 	}
 
 	return nil
@@ -53,7 +54,7 @@ func ApplyWritesToOffChainStore(data LedgerUpdate) error {
 func simulateFailureIfRequired() error {
 	if SimulatedFailureCount > 0 && transactionCount >= SimulatedFailureCount {
 		transactionCount = 0
-		return ErrExpected
+		return errors.New("expected error: simulated write failure")
 	}
 
 	transactionCount += 1

off_chain_data/application-go/transact.go

@@ -17,7 +17,10 @@ func transact(clientConnection *grpc.ClientConn) {
 	if err != nil {
 		panic((err))
 	}
-	defer gateway.Close()
+	defer func() {
+		gateway.Close()
+		fmt.Println("Gateway closed.")
+	}()
 
 	contract := gateway.GetNetwork(channelName).GetContract(chaincodeName)
 
@@ -42,29 +45,45 @@ func (t *transactApp) run() {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			t.transact()
+
+			if err := t.transact(); err != nil {
+				fmt.Println("\033[31m[ERROR]\033[0m", err)
+				return
+			}
 		}()
 	}
 
 	wg.Wait()
 }
 
-func (t *transactApp) transact() {
+func (t *transactApp) transact() error {
+	funcName := "transact"
+
 	anAsset := atb.NewAsset()
 
-	t.smartContract.CreateAsset(anAsset)
+	err := t.smartContract.CreateAsset(anAsset)
+	if err != nil {
+		return fmt.Errorf("in %s: %w", funcName, err)
+	}
 	fmt.Println("Created asset", anAsset.ID)
 
 	// Transfer randomly 1 in 2 assets to a new owner.
 	if utils.RandomInt(2) == 0 {
 		newOwner := utils.DifferentElement(atb.Owners, anAsset.Owner)
-		oldOwner := t.smartContract.TransferAsset(anAsset.ID, newOwner)
+		oldOwner, err := t.smartContract.TransferAsset(anAsset.ID, newOwner)
+		if err != nil {
+			return fmt.Errorf("in %s: %w", funcName, err)
+		}
 		fmt.Printf("Transferred asset %s from %s to %s\n", anAsset.ID, oldOwner, newOwner)
 	}
 
 	// Delete randomly 1 in 4 created assets.
 	if utils.RandomInt(4) == 0 {
-		t.smartContract.DeleteAsset(anAsset.ID)
+		err := t.smartContract.DeleteAsset(anAsset.ID)
+		if err != nil {
+			return fmt.Errorf("in %s: %w", funcName, err)
+		}
 		fmt.Println("Deleted asset", anAsset.ID)
 	}
+	return nil
 }

off_chain_data/application-go/utils/utils.go

@@ -3,6 +3,7 @@ package utils
 import (
 	"crypto/rand"
 	"errors"
+	"fmt"
 	"math/big"
 	"os"
 )
@@ -35,25 +36,32 @@ func DifferentElement(values []string, currentValue string) string {
 }
 
 // Return the value if it is defined; otherwise panics with an error message.
-func AssertDefined[T any](value T, message string) T {
+func AssertDefined[T any](value T, message string) (T, error) {
 	if any(value) == any(nil) {
-		panic(errors.New(message))
+		var zeroValue T
+		return zeroValue, errors.New(message)
 	}
 
-	return value
+	return value, nil
 }
 
 // Wrap a function call with a cache. On first call the wrapped function is invoked to
 // obtain a result. Subsequent calls return the cached result.
-func Cache[T any](f func() T) func() T {
-	value := any(nil)
+func Cache[T any](f func() (T, error)) func() (T, error) {
+	var value T
+	var err error
+	var cached bool
 
-	return func() T {
-		if value == nil {
-			value = f()
+	return func() (T, error) {
+		if !cached {
+			value, err = f()
+			if err != nil {
+				var zeroValue T
+				return zeroValue, fmt.Errorf("in Cache: %w", err)
+			}
+			cached = true
 		}
-
-		return value.(T)
+		return value, nil
 	}
 }
 

off_chain_data/application-go/utils/utils_test.go

@@ -1,20 +1,27 @@
 package utils_test
 
 import (
+	"errors"
 	"offChainData/utils"
 	"testing"
 )
 
 func Test_cachePrimitiveFunctionResult(t *testing.T) {
 	counter := 0
-	f := func() int {
+	f := func() (int, error) {
 		counter++
-		return 5
+		return 5, nil
 	}
 
 	cachedFunc := utils.Cache(f)
-	result1 := cachedFunc()
-	result2 := cachedFunc()
+	result1, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+	result2, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
 
 	if counter != 1 {
 		t.Error("expected counter to be 1, but got", counter)
@@ -25,13 +32,36 @@ func Test_cachePrimitiveFunctionResult(t *testing.T) {
 	}
 }
 
+func Test_whenCachedFunctionsErrors_returnError(t *testing.T) {
+	errorMsg := "error"
+	f := func() (int, error) {
+		return 0, errors.New(errorMsg)
+	}
+
+	cachedFunc := utils.Cache(f)
+	_, err := cachedFunc()
+	if err == nil {
+		t.Fatal("expected error, but got", err)
+	}
+
+	if err.Error() != errorMsg {
+		t.Fatal("expected error message to be 'error', but got", err)
+	}
+}
+
 func Test_cacheWrappedPrimitiveFunctionResult(t *testing.T) {
 	controlValue := 5
-	multiplyControlValueBy := func(n int) int { controlValue *= n; return controlValue }
+	multiplyControlValueBy := func(n int) (int, error) { controlValue *= n; return controlValue, nil }
 
-	cachedFunc := utils.Cache(func() int { return multiplyControlValueBy(5) })
-	result1 := cachedFunc()
-	result2 := cachedFunc()
+	cachedFunc := utils.Cache(func() (int, error) { return multiplyControlValueBy(5) })
+	result1, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+	result2, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
 
 	if controlValue != 25 {
 		t.Error("expected control value to be 25, but got", controlValue)
@@ -48,17 +78,23 @@ func Test_cacheWrappedDataStructureResult(t *testing.T) {
 	}
 
 	controlStruct := &GreetMe{helloTo: "Hello "}
-	greet := func(name string) *GreetMe { controlStruct.helloTo += name; return controlStruct }
+	greet := func(name string) (*GreetMe, error) { controlStruct.helloTo += name; return controlStruct, nil }
 
-	cachedFunc := utils.Cache(func() *GreetMe { return greet("John Doe") })
-	result1 := cachedFunc().helloTo
-	result2 := cachedFunc().helloTo
+	cachedFunc := utils.Cache(func() (*GreetMe, error) { return greet("John Doe") })
+	result1, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+	result2, err := cachedFunc()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
 
 	if controlStruct.helloTo != "Hello John Doe" {
 		t.Error("expected control value to be 'Hello John Doe', but got", controlStruct)
 	}
 
-	if result1 != "Hello John Doe" || result2 != "Hello John Doe" {
-		t.Fatal("expected cached results to be 'Hello John Doe', but got", result1, result2)
+	if result1.helloTo != "Hello John Doe" || result2.helloTo != "Hello John Doe" {
+		t.Fatal("expected cached results to be 'Hello John Doe', but got", result1.helloTo, result2.helloTo)
 	}
 }