fix: Maintain backward-compatibility with old bitstring implementation (

#1804)

For VC DM1.1 status lists, maintain backward compatibility with the old bitstring implementation where bits are set in the "right-to-left" order.

Signed-off-by: Bob Stasyszyn <bob.stasyszyn@gendigital.com>

pkg/doc/vc/bitstring/bitstring.go

@@ -24,8 +24,8 @@ const (
 // BitString struct.
 type BitString struct {
 	bits              []byte
-	numBits           int
 	multibaseEncoding multibase.Encoding
+	bitPosition       func(position int) int
 }
 
 type Opt func(*options)
@@ -43,19 +43,38 @@ func WithMultibaseEncoding(value multibase.Encoding) Opt {
 
 // NewBitString return bitstring.
 func NewBitString(length int, opts ...Opt) *BitString {
+	size := 1 + ((length - 1) / bitsPerByte)
+
+	return newBitString(make([]byte, size), opts)
+}
+
+func newBitString(bits []byte, opts []Opt) *BitString {
 	options := &options{}
 
 	for _, opt := range opts {
 		opt(options)
 	}
 
-	size := 1 + ((length - 1) / bitsPerByte)
-
-	return &BitString{
-		bits:              make([]byte, size),
-		numBits:           length,
+	b := &BitString{
+		bits:              bits,
 		multibaseEncoding: options.multibaseEncoding,
 	}
+
+	if options.multibaseEncoding != multibase.Encoding(0) {
+		// VC DM2.0 BitstringStatusList uses multibase encoding and requires bits
+		// to be set left-to-right.
+		b.bitPosition = func(position int) int {
+			return bitOffset - (position % bitsPerByte)
+		}
+	} else {
+		// Maintain backward compatibility with the previous implementation,
+		// which sets bits right-to-left.
+		b.bitPosition = func(position int) int {
+			return position % bitsPerByte
+		}
+	}
+
+	return b
 }
 
 // DecodeBits decode bits.
@@ -101,16 +120,13 @@ func DecodeBits(encodedBits string, opts ...Opt) (*BitString, error) {
 		return nil, err
 	}
 
-	return &BitString{
-		bits:              buf.Bytes(),
-		multibaseEncoding: options.multibaseEncoding,
-	}, nil
+	return newBitString(buf.Bytes(), opts), nil
 }
 
 // Set bit.
 func (b *BitString) Set(position int, bitSet bool) error {
 	nByte := position / bitsPerByte
-	nBit := bitOffset - (position % bitsPerByte)
+	nBit := b.bitPosition(position)
 
 	if position < 0 || nByte > len(b.bits)-1 {
 		return fmt.Errorf("position is invalid")
@@ -130,7 +146,7 @@ func (b *BitString) Set(position int, bitSet bool) error {
 // Get bit.
 func (b *BitString) Get(position int) (bool, error) {
 	nByte := position / bitsPerByte
-	nBit := bitOffset - (position % bitsPerByte)
+	nBit := b.bitPosition(position)
 
 	if position < 0 || nByte > len(b.bits)-1 {
 		return false, fmt.Errorf("position is invalid")

pkg/doc/vc/bitstring/bitstring_test.go

@@ -7,6 +7,7 @@ SPDX-License-Identifier: Apache-2.0
 package bitstring
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/multiformats/go-multibase"
@@ -53,6 +54,14 @@ func TestBitString(t *testing.T) {
 		err := bitString.Set(1, true)
 		require.NoError(t, err)
 
+		err = bitString.Set(14, true)
+		require.NoError(t, err)
+
+		err = bitString.Set(17, true)
+		require.NoError(t, err)
+
+		logBits(t, bitString)
+
 		bitSet, err := bitString.Get(1)
 		require.NoError(t, err)
 		require.True(t, bitSet)
@@ -89,6 +98,14 @@ func TestBitString(t *testing.T) {
 		err := bitString.Set(1, true)
 		require.NoError(t, err)
 
+		err = bitString.Set(14, true)
+		require.NoError(t, err)
+
+		err = bitString.Set(17, true)
+		require.NoError(t, err)
+
+		logBits(t, bitString)
+
 		bitSet, err := bitString.Get(1)
 		require.NoError(t, err)
 		require.True(t, bitSet)
@@ -117,5 +134,27 @@ func TestBitString(t *testing.T) {
 		bitSet, err = bitStr.Get(1)
 		require.NoError(t, err)
 		require.False(t, bitSet)
+
+		bitSet, err = bitStr.Get(14)
+		require.NoError(t, err)
+		require.True(t, bitSet)
+
+		bitSet, err = bitStr.Get(17)
+		require.NoError(t, err)
+		require.True(t, bitSet)
+
+		logBits(t, bitStr)
 	})
 }
+
+func logBits(t *testing.T, b *BitString) {
+	t.Helper()
+
+	var str string
+
+	for _, x := range b.bits {
+		str += fmt.Sprintf("%08b ", x)
+	}
+
+	t.Logf("BitString: %s", str)
+}