FAB-12987 Fix for statedb value format check

This CR fixes a bug that causes wrong decoding of channel config
persisted by the binary of fabric versions lower than 1.3.
In the presence of this bug, the older channel config stored by block-0
is interpreted as of new format. See Jira for more details

Change-Id: I22e728e13ddf4c6838e68b022de2478666c31d22
Signed-off-by: manish <manish.sethi@gmail.com>

Author: manish-sethi

core/ledger/kvledger/txmgmt/statedb/stateleveldb/value_encoding.go

@@ -13,7 +13,8 @@ import (
 	"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/version"
 )
 
-// encode value encodes the versioned value
+// encode value encodes the versioned value. starting in v1.3 the encoding begins with a nil
+// byte and includes metadata.
 func encodeValue(v *statedb.VersionedValue) ([]byte, error) {
 	vvMsg := &msgs.VersionedValueProto{
 		VersionBytes: v.Version.ToBytes(),
@@ -28,6 +29,8 @@ func encodeValue(v *statedb.VersionedValue) ([]byte, error) {
 	return encodedValue, nil
 }
 
+// decodeValue decodes the statedb value bytes using either the old (pre-v1.3) encoding
+// or the new (v1.3 and later) encoding that supports metadata.
 func decodeValue(encodedValue []byte) (*statedb.VersionedValue, error) {
 	if oldFormatEncoding(encodedValue) {
 		val, ver := decodeValueOldFormat(encodedValue)
@@ -49,7 +52,7 @@ func decodeValue(encodedValue []byte) (*statedb.VersionedValue, error) {
 }
 
 // encodeValueOldFormat appends the value to the version, allows storage of version and value in binary form.
-// With the intorduction of metadata feature, we change the encoding (see function below). However, we retain
+// With the introduction of metadata feature in v1.3, we change the encoding (see function below). However, we retain
 // this funtion for test so as to make sure that we can decode old format and support mixed formats present
 // in a statedb. This function should be used only in tests to generate the encoding in old format
 func encodeValueOldFormat(value []byte, version *version.Height) []byte {
@@ -62,7 +65,7 @@ func encodeValueOldFormat(value []byte, version *version.Height) []byte {
 
 // decodeValueOldFormat separates the version and value from a binary value
 // See comments in the function `encodeValueOldFormat`. We retain this function as is
-// to use this for decoding the old format data present in the statedb. This function
+// to use this for decoding the old format (pre-v1.3) data present in the statedb. This function
 // should not be used directly or in a tests. The function 'decodeValue' should be used
 // for all decodings - which is expected to detect the encoded format and direct the call
 // to this function for decoding the values encoded in the old format
@@ -72,6 +75,12 @@ func decodeValueOldFormat(encodedValue []byte) ([]byte, *version.Height) {
 	return value, height
 }
 
+// oldFormatEncoding checks whether the value is encoded using the old (pre-v1.3) format
+// or new format (v1.3 and later for encoding metadata).
 func oldFormatEncoding(encodedValue []byte) bool {
-	return encodedValue[0] != byte(0)
+	return encodedValue[0] != byte(0) ||
+		(encodedValue[0]|encodedValue[1]) == byte(0) // this check covers a corner case
+	// where the old formatted value happens to start with a nil byte. In this corner case,
+	// the channel config happen to be persisted for the tuple <block 0, tran 0>. So, this
+	// is assumed that block 0 contains a single transaction (i.e., tran 0)
 }

core/ledger/kvledger/txmgmt/statedb/stateleveldb/value_encoding_test.go

@@ -37,6 +37,10 @@ func TestEncodeDecodeJSONOldFormat(t *testing.T) {
 
 func TestEncodeDecodeOldAndNewFormat(t *testing.T) {
 	testdata := []*statedb.VersionedValue{
+		{
+			Value:   []byte("value0"),
+			Version: version.NewHeight(0, 0),
+		},
 		{
 			Value:   []byte("value1"),
 			Version: version.NewHeight(1, 2),
@@ -61,7 +65,10 @@ func TestEncodeDecodeOldAndNewFormat(t *testing.T) {
 
 	for i, testdatum := range testdata {
 		t.Run(fmt.Sprintf("testcase-oldfmt-%d", i),
-			func(t *testing.T) { testEncodeDecodeOldFormat(t, testdatum) },
+			func(t *testing.T) {
+				testdatum.Metadata = nil
+				testEncodeDecodeOldFormat(t, testdatum)
+			},
 		)
 	}
 
@@ -81,7 +88,5 @@ func testEncodeDecodeOldFormat(t *testing.T, v *statedb.VersionedValue) {
 	// decodeValue should be able to handle the old format
 	decodedFromOldFmt, err := decodeValue(encodedOldFmt)
 	assert.NoError(t, err)
-	assert.Equal(t, v.Value, decodedFromOldFmt.Value)
-	assert.Equal(t, v.Version, decodedFromOldFmt.Version)
-	assert.Nil(t, decodedFromOldFmt.Metadata)
+	assert.Equal(t, v, decodedFromOldFmt)
 }