feat: Add legacy format key codec for bytes in collections (#17104)

types/collections.go

@@ -44,6 +44,12 @@ var (
 	// state backwards compatibility.
 	// Deprecated: use collections.Uint64Key instead.
 	LEUint64Key collcodec.KeyCodec[uint64] = leUint64Key{}
+
+	// LengthPrefixedBytesKey is a collections KeyCodec to work with []byte.
+	// Deprecated: exists only for state compatibility reasons, should not be
+	// used for new storage keys using []byte. Please use the BytesKey provided
+	// in the collections package.
+	LengthPrefixedBytesKey collcodec.KeyCodec[[]byte] = lengthPrefixedBytesKey{collections.BytesKey}
 )
 
 type addressUnion interface {
@@ -135,6 +141,28 @@ func LengthPrefixedAddressKey[T addressUnion](keyCodec collcodec.KeyCodec[T]) co
 	}
 }
 
+// Deprecated: lengthPrefixedBytesKey is a special key codec used to retain state backwards compatibility
+// when a bytes key is used as an index key.
+type lengthPrefixedBytesKey struct {
+	collcodec.KeyCodec[[]byte]
+}
+
+func (g lengthPrefixedBytesKey) Encode(buffer, key []byte) (int, error) {
+	return g.EncodeNonTerminal(buffer, key)
+}
+
+func (g lengthPrefixedBytesKey) Decode(buffer []byte) (int, []byte, error) {
+	return g.DecodeNonTerminal(buffer)
+}
+
+func (g lengthPrefixedBytesKey) Size(key []byte) int {
+	return g.SizeNonTerminal(key)
+}
+
+func (g lengthPrefixedBytesKey) KeyType() string {
+	return "index_key/" + g.KeyCodec.KeyType()
+}
+
 // Collection Codecs
 
 type intValueCodec struct{}

types/collections_test.go

@@ -30,6 +30,10 @@ func TestCollectionsCorrectness(t *testing.T) {
 	t.Run("Time", func(t *testing.T) {
 		colltest.TestKeyCodec(t, TimeKey, time.Time{})
 	})
+
+	t.Run("BytesIndexingKey", func(t *testing.T) {
+		colltest.TestKeyCodec(t, LengthPrefixedBytesKey, []byte{})
+	})
 }
 
 func TestLEUint64Key(t *testing.T) {