Enhance Go off_chain_data for consistency

Add some methods to the parsing API within the Go off_chain_data sample
for consistency with the Node and Java implementations:

- ToProto() on Block, Transaction and NamespaceReadWriteSet.
- ValidationCode() on Transaction.
- Creator() on Transaction

Signed-off-by: Mark S. Lewis <Mark.S.Lewis@outlook.com>

off_chain_data/application-go/parser/block.go

@@ -26,6 +26,10 @@ func (b *Block) Transactions() ([]*Transaction, error) {
 	return b.transactions()
 }
 
+func (b *Block) ToProto() *common.Block {
+	return b.block
+}
+
 func (b *Block) unmarshalTransactions() ([]*Transaction, error) {
 	envelopes, err := b.unmarshalEnvelopes()
 	if err != nil {

off_chain_data/application-go/parser/namespaceReadWriteSet.go

@@ -27,6 +27,10 @@ func (p *NamespaceReadWriteSet) ReadWriteSet() (*kvrwset.KVRWSet, error) {
 	return p.readWriteSet()
 }
 
+func (p *NamespaceReadWriteSet) ToProto() *rwset.NsReadWriteSet {
+	return p.nsReadWriteSet
+}
+
 func (p *NamespaceReadWriteSet) unmarshalReadWriteSet() (*kvrwset.KVRWSet, error) {
 	result := &kvrwset.KVRWSet{}
 	if err := proto.Unmarshal(p.nsReadWriteSet.GetRwset(), result); err != nil {

off_chain_data/application-go/parser/payload.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/hyperledger/fabric-protos-go-apiv2/common"
+	"github.com/hyperledger/fabric-protos-go-apiv2/msp"
 	"github.com/hyperledger/fabric-protos-go-apiv2/peer"
 	"google.golang.org/protobuf/proto"
 )
@@ -12,6 +13,7 @@ type payload struct {
 	commonPayload *common.Payload
 	statusCode    int32
 	channelHeader *common.ChannelHeader
+	creator       *creatorIdentity
 }
 
 func parsePayload(commonPayload *common.Payload, statusCode int32) (*payload, error) {
@@ -19,7 +21,19 @@ func parsePayload(commonPayload *common.Payload, statusCode int32) (*payload, er
 	if err != nil {
 		return nil, err
 	}
-	return &payload{commonPayload, statusCode, channelHeader}, nil
+
+	creator, err := unmarshalCreator(commonPayload)
+	if err != nil {
+		return nil, err
+	}
+
+	result := &payload{
+		commonPayload: commonPayload,
+		statusCode:    statusCode,
+		channelHeader: channelHeader,
+		creator:       &creatorIdentity{creator},
+	}
+	return result, nil
 }
 
 func unmarshalChannelHeaderFrom(commonPayload *common.Payload) (*common.ChannelHeader, error) {
@@ -30,6 +44,20 @@ func unmarshalChannelHeaderFrom(commonPayload *common.Payload) (*common.ChannelH
 	return result, nil
 }
 
+func unmarshalCreator(commonPayload *common.Payload) (*msp.SerializedIdentity, error) {
+	signatureHeader := &common.SignatureHeader{}
+	if err := proto.Unmarshal(commonPayload.GetHeader().GetSignatureHeader(), signatureHeader); err != nil {
+		return nil, err
+	}
+
+	result := &msp.SerializedIdentity{}
+	if err := proto.Unmarshal(signatureHeader.GetCreator(), result); err != nil {
+		return nil, err
+	}
+
+	return result, nil
+}
+
 func (p *payload) endorserTransaction() (*endorserTransaction, error) {
 	if !p.isEndorserTransaction() {
 		return nil, fmt.Errorf("unexpected payload type: %d", p.channelHeader.GetType())
@@ -50,3 +78,15 @@ func (p *payload) isEndorserTransaction() bool {
 func (p *payload) isValid() bool {
 	return p.statusCode == int32(peer.TxValidationCode_VALID)
 }
+
+type creatorIdentity struct {
+	creator *msp.SerializedIdentity
+}
+
+func (i *creatorIdentity) MspID() string {
+	return i.creator.GetMspid()
+}
+
+func (i *creatorIdentity) Credentials() []byte {
+	return i.creator.GetIdBytes()
+}

off_chain_data/application-go/parser/transaction.go

@@ -1,6 +1,7 @@
 package parser
 
 import (
+	"github.com/hyperledger/fabric-gateway/pkg/identity"
 	"github.com/hyperledger/fabric-protos-go-apiv2/common"
 )
 
@@ -16,6 +17,10 @@ func (t *Transaction) ChannelHeader() *common.ChannelHeader {
 	return t.payload.channelHeader
 }
 
+func (t *Transaction) Creator() identity.Identity {
+	return t.payload.creator
+}
+
 func (t *Transaction) NamespaceReadWriteSets() ([]*NamespaceReadWriteSet, error) {
 	endorserTransaction, err := t.payload.endorserTransaction()
 	if err != nil {
@@ -37,3 +42,11 @@ func (t *Transaction) NamespaceReadWriteSets() ([]*NamespaceReadWriteSet, error)
 func (t *Transaction) IsValid() bool {
 	return t.payload.isValid()
 }
+
+func (t *Transaction) ToProto() *common.Payload {
+	return t.payload.commonPayload
+}
+
+func (t *Transaction) ValidationCode() int32 {
+	return t.payload.statusCode
+}